A quick tip for anyone that reads this... when you try to do failure analysis like this, don't EVER put the two broken pieces of metal back together. This changes the metal failure surfaces and can hurt our ability to find answers.
I write software for exactly this SEM. It always amazes me what can be done with those machines (I'm SWE, not a physicist). And trust me, this is the most basic type of analysis you can do in them. I have seen people heating golden nanoparticles to 700 C and observing how they started to jiggle. All while seeing individual atoms. I have also seen people micro-machining a few-nanometer-wide lamellas which are then analyzed in even crazier machines (transmission electron microscopes).
Aircraft mechanic of 8+ years. Drilled hundreds of thousands of holes in steel, aluminum, stainless, and composite. With the exception of a few specific drill processes, best shop practice is to step up in drill bit sizes by specific increments depending on material, thickness, and stack-up. I've witnessed very few of the drill bit failures you experienced with this drill bit and can say, with 100% certainty, it is a manufacturing defect. We've gone so far as to purge all inventory of bits from specific manufacturers, with similar manufacture date and heat treat lot numbers, that have exhibited failures like this due to the injuries sustained by mechanics. It's always nice to dive deeper into these different topics! Keep up the great work!
@@jorgeo4483 They just get sent back and replaced with a new batch, and then the manufacturer has to dispose of them. My bet is that they split during the twisting process, as blanks with a round shank and flat end are twisted to make the spiral, then are then rough ground, then heat treated and finally finish ground, with the final process being the final heat treating or coating. Either a batch of alloy that was too cold, or was not mixed properly, or was cooled down too rapidly in the forging process, led to the initial defect there that is where the failure started when it broke, and this first went to the tip when it was being twisted, and stayed there all the way. This bit was doomed to fail anyway, that split was bound to open up sooner or later, the forces on it made it split, irrespective of it enlarging a hole, or drill into the block from the beginning, that force was applied to the tip in the same manner.
I could not agree with you more. Indeed, my favorite sets of drills are pilot bits (mine are made by DeWalt) which have an integrated smaller bit that starts the hole followed by the larger bit. Whoever responded to James was full of crap. This bit was flawed.
@@flingshotlife Easy, just do not buy the cheap horor fraught bits unless you are prepared to use once. I have had good results using bits from tool suppliers, and Dormer makes good low cost bits. Just do not bother buying cheap, especially in sets unless they come from a tool supplier, or are branded from Dormer, Bosch, Hikoki, or any of the larger tool manufacturers, who have them made to their spec. Anything that comes as cheap sets, especially with a badge just placed on the box, is not the best, some are not even hardened steel at all, just ordinary steel ground to shape, because that is easier, and they twist straight the first time you use them.
I worked in a 7-acre Fortune 500 machining plant that heat treated 24/7. I was the QC manager, and failure analysis of this type (sometimes including our SEM) was an almost daily occurrence. I've prayed over many pictures of metal microstructure! Thanks for bringing back memories James!
Agree with the pre-existing fracture. That clearly occurred during the manufacturing process. The secondary fracture does not appear to have failed all at once. Your low mag optical photos at around 3:45 to 4:00 show evidence of fingernail-shaped “beach marks”. That is clear evidence of a fatigue failure. As external load is placed on the material, the fracture grows one cycle, the distance between consecutive beach marks. That says there must have been a repeated application of load that advanced the fracture surface the distance between the beach marks. Since that distance appears to be relatively coarse, the load could come from the advancement of drill via the tail stock. You twist the handle, stop for a fraction, then advance it applying more load (speculation on my part having bored many holes on a small hobby lathe.) The cross-section of good material keeps becoming reduced as the fatigue crack grows. Eventually the tendril of remaining material fails to support the external load (stress) and the material fails in final fast fracture, evidenced by the cup and cone appearance by secondary electron image of that last photograph you showed where you could see the little round inclusions sitting within the base of the cone. Those inclusions served as nucleating sites for the final fast fracture. I am a metallurgist, MS degree, with 25 years of performing failure analysis on a wide range of materials including steels, titanium, niobium, zirconium, and other structures. If you can get back on the SEM and get a set of low magnification secondary electron images, say 10 to 25X I think you will readily see what I’m talking about.
The one question I have about this theory is: Why did the fatigue crack meet up smoothly with the pre-existing manufacturer-error crack? I wouldn't expect that to happen unless they propagated from the same exact stress tensors.
@@avialexander the fatigue portion of the fracture took off from the preexisting fracture. There is an extremely high stress field at the tip of the preexisting crack….one that can easily exceed the yield strength of the material. The sharper the notch at the crack tip the more concentrated the stress field. This can be verified in that the tips of the thumbnails point in the direction of the crack elongation. This is not so much a theory as a well known observation of failure mechanics. In effect the failure had three distinct modes. The preexisting brittle fracture, the low cycle fatigue portion, and then the final ductile fast fracture that looked to be mostly in tension (the cup and cones were circular, not elongated as in shear. It’s like reading horse tracks or animal tracks in the old West.
@@Zircon10 I believe you may be mistaken about the beach marks. I'm not an expert, or even certified or anything, but they wouldn't occur on the trailing edge of a fracture, right? That's the fast fracture area. Also, normally we're used to seeing them on relatively shallowly rounded surfaces, like round fatigue test bars. But this was a very sharp corner, and you can see that the curvature of the beach marks becomes much more shallow farther away from the corner, indicating to me that the fracture was growing away from that edge, not towards it. Welcome your insight here.
Alex, the fatigue beach marks certainly can occur on the trailing edge of a fracture, especially if the mode of the fracture is totally different. The original fracture emanating from the split point of the drill has all the watermarks of a brittle fracture that may have occurred during heat treatment or was exacerbated by thermal stresses of heat treatment. The heat tinting of the surface of that fracture roughly matches that of the outside surfaces of the drill bit and likely occurred during tempering as that "straw" color is associated with low temperature oxidation. There are large beach marks near the core of the drill that have quite wide spacing. The beach marks you are talking about near the surface are the result of high surface stresses prior to failure. There is little cross-section to support the material at this point and it is not unusual to see secondary fatigue cracks, especially emanating from the surface. I hate to tell you this, but your interpretation is incorrect. The fracture started out as a manufacturing defect, progressed down the length of the bit in low cycle fatigue, and eventually failed in a ductile fast fracture when insufficient material was present for the load applied.
Enlarging holes is common. I do find if you don't allow the next larger size bit to load up at least half of it's point width, especially in soft material like aluminum, the bit is likely to dig, then grab and break. For example I wouldn't go from 3/8" to 1/2", but would go from 1/4" to 1/2". If you have to go up in size a little where the bit is likely to grab, then a really light feed will help keep it from digging.
Not only that, but one is wasting time if the increase in size is too small. The previous drill bit in every step of the sequence should be just slightly larger in diameter than the chisel point of the larger drill. Going in increments that are unnecessarily small at best only increases the number of operations to no good end, thus wasting time. There is a huge drop in cutting force as soon as the hole is increased beyond the length of the chisel point. Beyond that, the reduction in force is not that great, and as you properly point out, gouging and grabbing get more and more likely. This was not the case here, though. This was just a drill bit that was already cracked.
I don't think it was... Hard drills like this have no forgiveness for the sudden twisting of getting caught up in a hole like this with aluminum. Aluminum heats up and the hole contracts if your not drilling properly and his lathe basically grabbed that drill and twisted it to death from 0 to 60 in under a millisecond. If he used an HSS drill it would bend and not break.
This is something that works really well for me, at some point in time I heard a general rule of thumb for pre-drillng, the starting bit should be around 1/3rd the diameter of your desired size.
For many of us this is the way. My creed is that if you don't learn something new everyday you are missing out on life. You must drink deep of the waters of life, else why live.
Machinist are the last people you should ever share an opinion with. If you lightly suggest that they are doing something incorrectly, they will become very unstable. Nothing is more fragile than the heart of a machinist. BTW a own multi axis CNC machines.
@@wannabecarguy my company employs the country’s best machinists. Great people. Morally and spiritually stable. Excellent skills and craftsmanship. I’m happy to be a servant of them. Thank you TURBOCAM.
As a former field service engineer for an electron microscope company, I'm very impressed with your accurate and concise explanation of how an SEM works. I really enjoyed the video.
Hi James. Very educational video!! As a young graduate engineer about 50 years ago I was faced with a problem on a bridge job site. The steel girders were manufactured to old plans however the new transverse stressing bars would not fit through the holes in the beam web. The beams would have been equivalent to a Gr250 or Gr350. The problem was compounded as half the bridge girders had been placed in position high up over the creek bed. From memory, the holes needed to be enlarged from 1.5" to 1.625". The holes had to be drilled as the use of oxy/acetylene enlarged holes was prohibited. The contractor wanted a lot of money to crane down to the ground the already installed beams. A normally ground 1.625" twist drill would probably last one hole or bind and stall the drill. The solution was simle. I just ground the drill's cutting edge to square up the cutting edge to a near neutral front relief angle. This worked a treat. Having a near neutral front relief angle meant that the drill would not grab the work.
You can take a really long scan where you make separate images for each element. It can show where in the sample each element is present, and you can often get an idea of the composition of individual grains.
EDS is the X-ray spectroscopy in general, “EDS Mapping” refers to the colorful overlays showing the location of different elements in the field of view like you’re describing. Most systems do both.
I spent a few years in a machine shop that's been in business for around 60 years. It was pretty standard known not to enlarge holes with a drill if you have any other option to enlarge the hole. I was taught the tip grabbing into the material does a lot to hold the drill centered. That when a hole is enlarged, it can cause vibration in the drill which can uncenter the drill causing a higher force the flutes can't handle
Right, if you jam one side of the drill against metal and not that v in the center then ... surprise! It will fail on the side of the drill like this. It's fine to do but I don't know that it would be best practice, everything in me screams you gotta bore that sucker out with a boring bar. I think best practice is you make one hole and bore it out, making two with a drill is misguided but also who cares it works often enough and breakage is a part of business
In the production CNC world I never spot or pilot dill holes. If you are using crankshaft, four facet or most any variation of NC point it isn't necessary. Sumocham, KM Go drills, Mits or Sandvik will prefer you drill the biggest diameter first in the case of stepped holes. Most manual machines don't have the thrust, spindle speeds, HP or the necessary guarding to run at mfg recommended drill speed and feeds. Running manual machines, what you did was prefectly fine. The drill was defective. Even the best drill manufacturer gets a bum drill from time to time. I had a run of a dozen 1/4 - 20 Taps from a highly reputable mfg blow up on every hole during a turnkey one time, switched brands and tapped hundreds more before the gage started getting tight. Stuff happens.
Well, yeah. CNC is very different in a lot of ways than manual machining. For one thing, a CNC machine doesn't get tired or run down when pushed close to its rated limit.
I have always been taught to not pre-drill except on big drills where you need enough to accept the chisel edge and that is to reduce the pressure it takes to shove that through the steel. The 135 degree split point are made to not wander with the grind and the thin web. In soft material like aluminum or plastic the drill is more likely to "thread" its self in. I have had the MT4 mounted chuck get yanked from my spindle with drilling Delrin that has an existing hole. I look for core drills or "Dreamers" for that if I have them (that is rare). Cool stuff man, I appreciate it!
I've experienced the same thing in UHMW, Teflon, and Nylon. I switched to a hand ground HSS boring tool in those situations. Always funny to see the looks of people when the part pulls outta the chuck too.😂
Ah, micro-cracks: those horrid things that are almost never found before it's too late. Seeing that one can silently and stealthily sit in a drill through use in multiple projects before becoming a failure point makes me sympathize with aircraft and bridge engineers all the more.
I had an identical failure with a DrillHog drill. In my case the flute broke off as soon as the drill hit the material. They did warranty it. It looked exactly like your failure, with the old and new broken areas clearly different. No doubt in my mind it's an artifact of the manufacturing process. Nothing is perfect, and I've gotten good service from all the rest of the drills I've bought from them.
It could be a common failure and the best QA is to ship them anyway and honor the warranty for the ones that they couldn't reasonably QA in house. I.E. You do the QA.
We use cobalt to drill the initial pilot hole, then switch to a conventional bit for opening up the diameter. What our machinists have found is that the overbore/opening up procedure adds excessive unsupported shoulder loads to the hardened bits causing breakage. Using softer HSS only requires the shoulders to be sharp, and the softer steel can absorb the micro vibrations with no issues. And the guys actually have contests to see who can sharpen their bit shoulders the finest. Much easier to touch up shoulders than pointed tips. Just our two cents from the guys here at the shop.
I actually came to the complete opposite conclusion! If you look at the crack at the rearward side, where it broke at the cutting edge, you'll see "beach marks." These are characteristic of a fatigue fracture initiation site, and that was my first clue. I was suspicious of the idea that the bit could be cracked from the factory so severely down the middle and not chatter immensely or break early. Another characteristic of fatigue fracture is striations in the "fast fracture" portion of the break, when the material finally gives way, and we see that in the tip-ward part of the fracture. One more thing: brittle vs. ductile fracture release energy in very different ways, and I think that may explain the oxidation. A brittle fracture releases energy as vibrations, and those dissipate throughout the metal as the sound is absorbed into the bulk material and other objects it's connected to. However, ductile fracture releases most of its energy into the material that is actively being stretched! That means, your ductile fracture surface was going to be very hot when it opened up and got exposed to air, which I think explains the oxidation (in addition to a lot more surface area to react over). And finally, the location of the transition between the colors. It's right at the point where the web of the drill starts, the point at which the cross-sectional distance across the fracture stops decreasing. I'm pretty sure this is due to the transition in stress direction from a mostly pure head-on shear crack to a side-loaded torsioned crack, and that also explains why it did not crack down the middle, but instead went to one side of the center of the torsional axis. Take this all with a grain of salt, I'm just a mechanical engineer who got really into materials in college, not someone who does this for a living or knows my stuff. P.S. @Zircon10 has a good explanation for why I'm wrong about this, and is actually a professional.
I don't think it was a full-on fracture coming from the factory. For one thing, that might have been pretty visible before the separation occurred. Rather, I suspect it was a micro-fracture, basically an incomplete fracture that produced a weakened area in the bit that eventually separated under heat and stress. Your explanation of the Oxygen contamination of the fracture is possible, but I suspect incorrect. Oxidation takes time, and the environment of a ductile fracture is not going to be highly uniform nor likely to be comparable to the environment during heat treating. The fact the concentration of the O2 in the fracture is virtually identical to that of the exterior of the bit suggests to me its presence was due to the heat treat process, rather than to the ductile deformation. I certainly cannot say with any sort of authority you are incorrect, but I suspect you may be. Either way, however, it is perfectly clear this bit was definitely flawed. I have broken a small number - very small, I am happy to say - of small drill bits in Aluminum by inadvertently allowing the bit to clog. Looking at the video, I am quite confident the bit was not clogged. Look at the chip coming out of the Aluminum. That hole is not clogged. Furthermore, I have *NEVER* broken a bit anywhere nearly this large in any medium whatsoever, and certainly not when a properly sized pilot hole is employed.
This is what I tried to explain in his last video but not as technical as you. Great job. I've seen this happen myself with a lathe. People will tell him they drill holes all day and have never seen this but I'll bet they drill vertical holes. Gravity, his taper, drill chuck, and the sudden load change from the tip of his drill to the edge getting caught in his hole have a lot to do with this. In his last video, it's clear that his tail stock was hanging out way too far and the pressure on the tip of the drill was too much causing the hole setup to flex... This flexing made the flute of the drill get caught on the inside of his hole and all the inertia of the spinning lathe chuck just snapped that hard drill (which would not have happened with an HSS soft drill) At the same time you could see the drill and chuck get pulled off the taper just a tinny bit. James knows his stuff but just like most machinists I know don't like to admit to being wrong about something unless you can repeat it for them. This could be done with his setup over and over...
@@Jeralddoerr Uh, nope. I have been machining for nearly 40 years, and done many thousands of horizontal holes. Except when drilling small holes, I always drill a pilot, and then step up to larger and larger drills.
@@williamsanders6092 breaking a drill or two myself in 20 years of home machining on my lathe EXACTLY like this! Also, I worked at a company that sold tooling for 6 years... That's all..
Looking forward to half the stuff in the shop being imaged in a SEM because of the potential sponsorship deal going through. Also thanks to you and your friend for teaming up to make this cool video. Friends are great. Friends with cool tools are *really* great.
This was a great video. Failure analysis is such a fun road to go down. As a retired rocket scientist I have had the opportunity to be involved in a number of Failure Analyses, some with catastrophic (and adrenaline inducing) events. My favorite event was watching ceramic catch on fire. Cheers!
James, some 50 years ago I got my degree in material science way back in Sheffield, UK and those semi circular bands in the failure pictures, to me, look exactly like the classic fatigue type failure. Normally fatigue takes many cycles to show evidence but with that material being so brittle each rotation of the bit whilst cutting would add a torque to propagate the crack some more. I agree that the dark area was probably formed at manufacture as the rounded smooth rather than angular structure of the crack surface, to me, indicates some elevated temperature or carburising process. Are the drill bits quenched in an oil bath as part of the heat treatment? Alloys of steel can be quite complex and getting the composition just right for the intended purpose is akin to the black art of alchemy; in general the interstitial nodules are there to pin the dislocations and increase the resistance to deformation but the size and distribution of them is critical and usually requires some complex heat treatment process to get it just right. I n summation I think you got it just about right and the drill supplier should be contacting the manufacturer regarding their below par quality control.
It’s pretty obvious it’s a fatigue failure but there isn’t enough information about the drill’s life. How many cycles had it done or was this the first use? Was it dropped? I see the classic fatigue fracture line running along the drill axis that are coming from the tip. That rules out the whole dark area being a factory defect although I couldn’t rule one out at the tip. It had to work in torsion to create those fatigue lines of those colours as the post fracture oxidation needs time to set in. I do like your line of questioning James with the colour change but you simply overlooked some evidence that is significant mate, and that changes the whole line of investigation. BTW I’m an Aussie mechanical engineer with endless curiosity which is how I ended up studying after 10 years as a soldier. I worked mainly on guided and unguided things that go boom, but also armour and tier 1 motorsports. So if you go back to the footage and see what looks like rows of sand dunes running along the length of the drill in the older fracture area, each of those is a fatigue fracture expanding one load cycle at a time. If your scope could get an oblique angle with a lower light angle it should pop out. I’d hazard a SWAG that you used it and expanded the fatigue failure, put it away and then the next time you used it a few days later it failed. I could be wrong and that’s okay too but I have seen similar and was lucky enough to study failure analysis and non-destructive testing with the folks considered the best in the game in Oz. Still doesn’t mean I’m right 😂
any drill bit with a reduced relief (back cut) on the trailing edge is not designed for enlarging holes.. at least that is what I was taught and my personal experience has proven it to me as well.. they always seem to shatter
Well, it depends upon the material being worked, but I don't think that was a reduced relief drill bit. What's more, as he pointed out, in that situation, the bit shatters (as you say). I have never seen a bit split along its spiral like that.
When I was in high-school there was a hiproduction machine shop across the street I walked over to and apprenticed ran screw machines went threw alot of drills we had six 1/2 cobalt drills from Enco now MSC did same thing split like that looked just like that! They sent us new ones hell they chatterd in the hole they were split also switched away from that bit for a while problem went away orderd them again never had a issue again 🤷♂️
I bleave it's quality control of a product . There a big difference between work load stress- chip weld feed rate ect think its plan and simple defective.
@@peterfitzpatrick7032 Well, no. First of all, most wood types and most plastics are softer, and there are quite a few softer metals. Of course the softness of the material is not the only consideration for loading, but I doubt anyone has ever broken a drill bit due to excess torque when drilling balsa wood.
I work with SEM, FIB, TEM, and STEM imaging systems for work doing failure analysis. I also use EDS and EELS analysis for material composition analysis. This was a very fun video to watch. If your friend has access to a STEM or TEM ask them to to an insitu lift out at the transition and then image it in a STEM or TEM and perform ELLS or EDS on it looking for oxidation or a change in crystalline structure. Some of the pulling your seeing is pre stress failing due to heat and some is from the time a failure would wager too. Would be interesting to see the material analysis report.
Wouldn't the drill sample be far too thick to do TEM or EELS on? I thought the sample thickness needs to be less than a micron for the electrons to penetrate.
@@cameronmcguire5025 that’s the purpose of the insitu lift out, you pull a small section out using a FIB and then thin it to electron transparency for imaging and analysis.
@@Human_OU812 oh okay, I'm not too familiar with TEM and FIB, I'm a graduate student studying studying the use of EXAFS and XANES and I haven't come across those terms you're using before. I'll have to look into that.
Very nicely done. A few things to remember when doing SEM/EDS analysis. First the secondary/backscattered image is a surface effect and backscattered is average Z (atomic number dependent), so darker is lower, brighter is higher Z. So backscattered is good for quick average Z grouping. EDS however is volumetric, that is the x-rays come from the excitation volume below the surface. Classic tear drop effect. The electron acceleration voltage determines how far into the sample. So you can play games with how far below the surface by adjusting the acceleration voltage. Of course, the lower you go in voltage, the harder it becomes to identify elements from the lack of excitation lines. Typical acceleration is 1.5x the lines of interest. Also doing EDS on a non-flat surface become tricky as the x-ray takeoff angle (to EDS detector) varies and the math becomes impossible to calc accurate weight percent of elements. Flat, polished surfaces only for serious EDS analysis. At one time we had two SEMs with EDS detectors in house. Lots of fun. I miss them.
Like you mention, you have to be careful about assuming the height of the histogram peak is proportional to the amount of the element present. The peaks represent number of X-rays received which is a complex result of many factors. Comparing Cobalt peak in one sample location relative to another location is generally safer. Trying to compare e.g. Cobalt peak height to Iron peak height at the same location has much less meaning. Sample prep and software tools exist to try and estimate relative proportions more accurately, but in my experience this was very uncommon in casual analyses. As someone else mentioned, the window on these detectors frequently block or seriously attenuate X-rays from lighter elements like Carbon and Oxygen so those peaks often aren’t super accurate.
From my limited experience (as a co-op for GE Aviation doing metallographic analysis, materials science background), I'm only 3 minutes in and your interpretation seems right to me. The bright silvery failed surface is what failed in tensile overload, while the oxidized surface has obviously seen life. This is actually how some aerospace investigations are evaluated (you can sometimes count the number of cycles a failed part has seen based on the different oxidation state colors (forms a series of color gradient bands, a different color for each # of 'cycles' that part has seen). Obviously the more oxidized a surface is the more time it's been epxosed to the elements or whatever environment it operates in. This video brings back memories of interepreting LCF (low cycle fatigue), HCF (high cycle fatigue), and basic metallographic failure analysis, loving it! Will continue to dig in! Since it seems you have ready access to an electron microscope, you could do EDS on any specific points of interest and determine what elements are present at that location (ie, when you mentioned the precipitates (nodules) in the surface that you expected were tungsten, if you did EDS on one of them you could confirm (ask whoever does your electron spectroscopy, they'll know). You could also confirm the oxide presence in the exposed/previously cracked surface using EDS, finding a lot of oxygen and the other elements present in the the composition. Compare that to an EDS of the tensile overloaded.
James,I have had 2 very similar failures with 8% Cobalt HSS drill bits in the past. In both instances you could clearly see a flaw had existed before the drill split apart with the same different colour and grain structure features as seen on your broken drill. It just happens on rare occasions that a drill bit has a flaw in the material stock or a flaw occurs due to some fault in the heat treating process and it gets missed by quality control. The investigation with the electron microscope was fascinating.
First of all, thank you for this very informative video, and all the others before! I was taught that pre-drilling is done to avoid high axial loads on the drill(-ling machine), which come from the unfavorable geometry of the drill in the central area, where it only displaces the material, rather than cutting. Even with the split point grind, the geometry in the web area of the drill bit isn't ideal. The recommendation is to pre-drill with about the size of the cross width of the web, or about 20% to 30% of the bigger drills diameter. Usually holes under 8 or 10 mm don't need to be predrilled (would require a tiny 2mm to 3mm pre-hole).
I was taught that IDEALY the pilot drill size should be the dia. of the center web of the finish size drill. That's fine if you have a high horsepower machine, but most of us don't so we need to step drill. Also: I have broken bits while step drilling on the drill press but never the lathe. I believe this is because with lathe drilling the feed is controlled by the tailstock feed screw, while on the drill press it's your hand on the handwheel, so if the drill grabs it will be pulled away from you.
@@rockmonkey37 That's the only thing that seems to work in plastics that have been pre-drilled or need through drilled. Will pull the part out of the chuck when it grabs (when it grabs, not if)
honestly i enlarge holes almost daily on work from 14.2mm to 22mm so 4.1mm per side and i never had a drillbit fail on me like in the video.. and i run it at insane feedrate mind you.. 350rpm with 350mm/min feedrate (1mm per revolution). (normal Hss drillbit aswell..) oh and 50mm deep, normally like 60 holes per plate.. and the drill withstands all 60 holes.. ( i do have to regrind it after a plate due to excessive wear, because of the feedrate tho..) SO in my opinion it does not matter if you enlargen a hole or not, it shouldn't fail like in the video period.
Just noticed 100K finally, you deserve 1M + and more. I really enjoy your down to earth approach, you’re personal deep dives and sharing your insight while doing so.
In school I was definitely taught to not enlarge holes with drills. At most, a pilot drill avoid be the diameter of the chisel tip of the large drill. Obviously, that's a sort of "horsepower elitism" there. Smaller hobby machines can't drive big drills outright. But yes, enlarging definitely concentrates the stress on the outer edge of the drill, and can cause extra wear and failure. And it can cause drills to bite and self-feed, which also increases stress.
I think you've proven well that there's something up with the manufacturing of the drill here, but that doesn't also mean that user error isn't a factor. I think they're 100% doing the right thing replacing the drill, but also pointing out that technique plays a factor.
The fracture surface has "beach marks" which are evidence of metal fatigue. The "beach marks" are the curved lines that start at the edge of the drill and progress towards the center of the drill. Once the fatigue crack is deep enough, the material will fail suddenly. Your analysis is correct in that the drill did originally have a longitudinal crack since there is oxidation on a portion of the separated surface. When the drill was loaded during drilling, the portion of the drill that was separated from the body of the drill was exposed to multiple loading cycles which lead up to the fatigue failure. Again, your analysis is correct, but I did not hear any mention of the fatigue failure that the "beach marks" are evidence of. I am a mechanical engineer with 36 years of automotive experience and have many years of failure analysis experience so the "beach marks" are something I am very familiar with.
I'm a former materials science technician who ran an electronic microscope for several years. I also have a physics degree. Great job explaining, and I fully agree with your conclusions. You just gained a subscriber!
We all knew it was a "bad bit" but to break it down with the education on an electron microscope was great! Thanks James. The "call me" at the end was awesome.
Dang, must be a pricy drill bit if they were like "yeah I'll replace it and throw in the associated bit we claim you should have used" 🤣 And then you do the hard work of failure analysis for them 😁. Thanks for the very nerdy and excellent look at the drill under the SEM, I really enjoyed the explanations.
Just good customer relations, and also a company that offers a lifetime warranty, not expecting much use, because most of the time a drill bit fails it is due to abuse, or it just wearing out. Here it was definitely a latent defect in the steel, and they probably have had a few of the same batch fail already and been reported.
The only reason to pre-drill or pilot drill a hole is to clear the web. It’s a lot harder to push a drill when you don’t. In my experience the least times you step up in drill sizes before the final, the better. A split point has practically no web at the point so generally they don’t need pre-drilled… so long as you aren’t using a cordless drill.
@@Clough42 you should check out Breaking Taps channel and some of his homemade equipment. An autodidact like yourself might get stuck down the rabbit hole though :)
Maybe ask your friend to scratch an carefully dent an pull a wire off inside. Then they might just replace it? Colleges have lots of money. Then pull it out of the dumpster... Or maybe they have and older one in storage? I did like the video. It was very interesting. Being able to tell what elements are present would be handy. No more mystery metal! I know nothing about SEM but for what it is worth based on what you were saying an showing I agree with your findings. I am going to see if I can get a much higher magnification lens for my old B&L microscope. I suddenly want to see as much as I can. This rabbit hole may get very expensive!
That takes my mind back to the late 60s, I took an industrial Physics course in High School and one of the things overed was Metrology and Metallurgy, we had to test metal samples to the failure point. the samples were metal rods which we stretched until they broke, usually with a snap that sounded like a gun shoot, which made everyone jump.
I have black belt electron scanning microscope degree and PhD / ScD of Drilling and after analyzing your video I can say that this drill is broken. Thank you.
I worked with Carbide for many years as I was a machine operator in a carbide tool manufacturing plant. I've seen many tools break or come apart such as your sample. Carbide is "sintered". That is, the composites making up carbide are mixed together as a powder and then heated under pressure to create a solid. The gold color on your sample almost certainly means it was fractured AFTER manufacture.This is why, of course, some traces of the coating appear on the fracture. It is sometimes very difficult to see a fracture on a particular tool that would lead to it cracking. Of course, we didn't have the use of a SEM while making tools. We would sometimes drop tools to see if they broke apart if we were having problems with a particular batch of carbide. This tool pictured had a fault from the sintering process before it was ever fluted. We found that certain suppliers of carbide were prone to this problem and therefore we tried not to use them. Certain composites (called grade) of carbide can be in extremely short supply, especially if a particular type tool is specified on the print. Generally speaking; the more harder-acting the carbide tool is, the more expensive its cost.
When I programmed CNCs in the 90’s, we almost never programmed pre-drilling. Only for very large diameter drills. We almost always center drilled and then just plunged in the drill. The advantage of the CNC is of course that you always get the correct cutting and feed speeds.
I agree that expanding existing holes can be a bit hard on the drill but sometimes it is required. Not many home shop machines have the power to push a bigger bit without a pilot.
There are rare and expensive 3- and 4-flute "core drills" for that, although when I asked Somta about them they said, "they start at 14mm and they're morse taper shank only".
huh..?? I work in a foundry for the mold department, we have plates out of normal soft steel (S253JR) and we predrill the holes on the CNC and then turn the plate over and enlarge the holes on a drillpress from 14.2mm to 22mm diameter so 4.1mm per side, depth is 50mm deep, there are roughly 60 holes per plate (2plates needed, top and bottom) and i normally run the drill with like 350RPM and 1mm/revolution so 350mm/minute feedrate. Thats insanely fast if you look at it in person. You know what never happend? that the drill split like in the video. i can do 1 plate before i have to sharpen the drillbit again. (duo to the excessive wear because of the high feedrate) And thats with a normal HSS drillbit mind you.
Absolutely TRUE! However, you should use a slow feed rate on the drill to prevent grabbing. Large increments are easier on the drill and work fine. The goal is to relieve the tip, which has awful cutting geometry.
Great video! I am a PhD student using scanning/transmission electron microscopy to study ceramic crystal structures, and I thought your explanation was very thorough and concise. One thing I thought I would mention is that EDS/EDX (Energy Dispersive X-ray Spectroscopy) for elemental analysis is usually only semi-quantitative at best, at least without a reference sample. Also, unless you have a very specialized detector, the technique is inaccurate for detecting elements below an atomic number of ~11 (this is due to the low energy of the characteristic x-rays these elements produce). I suspect that the high carbon (atomic number 6) presence in this sample is not only the carbon present in the alloy, but also carbon contamination from the environment/touching it with your bare hands. You can alleviate some of this contamination by plasma cleaning the surface prior to loading, but environmental contamination is always going to be present to some degree. Oxygen is also
The main thing a degree teaches you is how to learn, often the knowledge you gain is of limited use but the ability to research and learn lasts forever. As for your analysis I'd say that was pretty good, I'm not an expert but I've done some SEM analysis in my undergrad days and everything you say seems right. My PhD was in a different area of physics, I really like your thirst for knowledge and the fact you have a friend with access to an SEM.
Thank you for an interesting and thought provoking video! I find that the most significant problem with the autodidactic approach is that there simply are not enough hours in each day, particularly when you have to exchange a portion of those hours in exchange for money. 🙂
Enlarging existing holes is normal and should not lead to failure of that sort. That said, ideally the right tool for the job is a "core drill" (not to be confused with the other type of "core drill"!) which has three flutes and an extra thick web. You get better roundness and even less chance of breakage.
As a Knifesmith, I've drilled many holes in steel, never seen a bit break like that, however, after doing snap tests on many steels, I noticed straight away the difference in grain growth in the broken section. 👍🍻🇿🇦
Hi James, did you think about breaking that tip of the drill in another place to see if the whole tip has a different color and then it can be attributed to the heat treatment? It should be a simple whack with a hammer and see if it has the same color... right?
While it would be a fairly rudimentary test at this point, if you happen to have a set of Rockwall hardness files, I'd be curious to see if the off-colored areas test significantly different to each other. The surface of hardened tools, especially with a topically coated treatment, should be at least a grade higher than its core. That's not indicative of a manufacturing defect by itself as stress fatigues can certainly affect a steel or alloy's hardness up to the moment of failure (and/or induce it), but a coating applied to a tool that either failed heat treat (or in specialized cases, cryo treat) would show up further away from the failure site if you're up for a full post-mortem.
Oh, such memories! But also, I share 100% the lifetime interest on all kinds of odd topics. Sort of everything between ground and sky (including chemistry, metallurgy and astronomy). All of those far away from my professional education. However, at one point I participated in troubleshooting of a paper machine dryer cylinder with a boss, who was even more skilled on various strange things than I was. He decided we needed to get photos of the cylinder surface morphology, using SEM. As we could not take the 16 feet diameter cylinder to a SEM machine, we made imprints of certain locations of the cylinder using some plastic. The SEM operators plated our imprints with metal and then scanned it. Unlike optical microscope, the SEM process had a marvelous depth of field, so the imprint piece could be tilted at will and everything still remained in focus. Marvelous pictures! Your story also relates to another past experience of mine. At a time I was presented with a challenge of an unsteady GTAW (TIG) welding arc. Turned out to be a split tungsten electrode. It also was a manufacturing issue -- inadequate bonding of the powder in the sintering process. That memory immediately flashed in my mind when I saw the split of your drill bit.
I used to work at a Test House with a SEM. I was told that when things break NEVER try to put the parts back together. It's better to leave them apart as any further contact could mask the reason for the failure.
Interesting video and information. In my life before retirement, I was involved with Overhead crane maintenance. A large part of these cranes consumable parts are the wire rope that is used as part of the hoisting of the load. One of my many training materials the different types of failures of the steel wire when a wire rope failed prematurely. What was interesting in the literature was the electron microscope example photos that showed the difference in the wire failures. With that you could examine and determine most of the time the root cause of failure by just cleaning and evaluating the break with a simple magnifying glass. Great stuff. In all the years that I drilled holes and observed holes drilled, I never seen a drill bit fail that way. When you showed the failed bit I was curious as you, why it failed. Thanks for sharing.
Great video. In my work I have review many failure analysis and have seen similar failures of heat treated parts, one that comes to mined is s large spring. I agree that the darker area was created during the heat treatment (oxidation). I see beach marks in the gray area closer to the end of the oxidized area showing the extension of the cracking caused by the local overloading. this continues while the drill continues to cut until the brittle failure denoted by the course grain and cleaving to the end of the failure.
Shop practice != Best practice. As even many comments here show - many people just do as they have always done. They start at a shop and get told "for XY hole pre-drill with YZ" and afterwards never question that. Drill-manufacturers in general suggest pre-drilling for hole larger than 10mm/ 0.5 inch when working with metal (that is just roughly, depending on the manufacturer, drill, material, feedrate etc ). had a similar experience when doing my first reflow-soldering back in university. Had my PCB, soldermask, solder and components prepaired, as well as guideline for the solder-profile of the parts and the solder it self. Got to the local electronics-group and started reading through the manual of the reflowoven they had there when one of the seniors came up to me and explained to me how to use the machine and which settings to use..... yeah all wrong: too hot of a starting temperature, too fast rampup, waaayy too hot of a top-temperature, too short on the max temperature, too slow cooldown at first and then basically shock-cooling at the end. No wonder the guys there kept complaining that they only got bad results and about how much the need a better machine to get better pcbs..... experiment
I've always been taught pre-drilling was reserved for large drills where feed pressure would be high, too much heating at the web, hard materials, or location was critical and that the pre-drill should be approx the size of the web of the larger drill. My experience tells me the response from Drill Hog is for smaller drills. 🤔
I love the break-down and to have it end with 'so what are we going to do?' "Nothing" I found somewhat humerous considering. Will be looking at your other videos after this!
Very interesting video. I almost always drill a pilot hole and have never heard that it could cause a drill to break. If you look at that broken drill section where the clean break goes into the complete drill I believe you can see the darker section continuing into the rest of the drill. 4.42 in the time stamp.
From my education as an Mechanical Engineering Technician at Purdue University, the dark area at the tip tells me that that area was already cracked. The crack allows oxygen in to that surface and causes that oxidation! Part of my education at am MET included the study of failures, such as this, and that dark color is indicative of a pre-existing crack. The light area is in fact a brittle fracture that happened as you drilled! As to your question about pre-drilling holes ... that is in fact standed machining practice.
You can see the fatigue benchmarks on the fracture surface in the silver colored area. Area shown around 11 minute mark is fatigue crack propagation area. At 11:33 mark, dimpled rupture is noted. Overload fracture. Within cups are carbides. Pre existing defect.
You continue to surprise. That is quite an analysis! This level of metalurgical analysis is not common to home shops! Lots of great comments below, but I have routinely drilled a smaller hole, then a larger one. Aluminum is soft, with good control of the feed, a decent bit should handle the job. It is true, though, that machinists routinely cut aluminum with carbide bits at very high rpm, which would minimize the depth of cut per revolution.
I was taught in the workshop, many years ago, to step up drill sizes to reduce the workload on the bigger bits. I've always done that and never had a bit fail while doing so.
Ok, now I've gotten to the hole enlargement part. I agree with the manufacturer. When I worked under a part time machinist for a short time, he said it was standard practice to use a pilot hole. After watching and doing this myself, I realize the larger bit will tend to grab a self feed too fast if the diameter was close. I suggested to him that the pilot should be no more than one third the full diameter. This keeps the included shoulder angle in play and prevents too fast a feed, while keeping the larger bit tracking true.
I had the same failure about 8 years ago, Sutton 10mm HSS Cobalt drill. Used for the first time and it fell to bits on contact with the job. Unfortunately Sutton Australia didn't even bother replying to my email asking if I could have a replacement. In my email "Upon inspection one can see the outer coating has actually plated the inside of the drill i.e. there was a crack in it during the manufacturing process. " . In retrospect not a coating, just an oxide layer as described in this video. Perhaps HSS Cobalt drills are more prone to cracking during manufacturing than other drill types.
I’ve seen people enlarging holes with drills but I was taught to spot drill and generally not to pre-drill for a drill. I do pre-drill for endmills, though.
Being a hobbyist blacksmith my first thought was that it was a cold shut that possibly formed when they made the grooves by drawing the material through a die and they probably didn't cut enough off the end before moving to the next step.
@@vincentguttmann2231 that's when the steel is folded onto itself (kinda like a wrinkle). If it happens at welding heat then it'll just fuse together. But you don't forge at welding heat for a lot of reasons and that means a small cold shut can get into the piece. Once it's there it can be very hard to get rid of, if you can even tell it's there as they can be impossible to see sometimes. Easiest way to get rid of a cold shut is to literally grind/cut the thing out. A cold shut could definitely have caused this failure. Although, my first instinct thought the blank was put into a hot heat treating oven when the blank's end was too cold (potentially from the thing that grips the blank being too cold and sucking the heat away). If the tip heated up too quickly then it could also cause excess stress and fail in a similar way.
As far as I know, only large drills >1" are forged then twisted. Everything I've seen for smaller drills is ground/cut to shape. I'm pretty sure there are probably some drawing processes used someplace for smaller drills though. There are flute grinding marks present on this drill, but that doesn't mean it wasn't drawn and then finished ground. What's weird is the crack doesn't appear to originate from a corner or stress riser. Perhaps thermal shock while the tip was being rough ground? I can totally see a cold shut being the origination as you describe.
@@Dreddip You can see the inclusion though, where either there was incomplete mixing in the melt, or a tiny bit of slag that was deep in the original rod.
I like the analysis, even though it's basically just telling us that there was a manufacturing defect and the solution would be to take a new drill bit and finish the work. The important lesson here is that this also tells you and everyone else what to watch for in case something serious has happened. That could make a huge difference when it comes to identifying who's responsible for an accident - or not responsible. A few years ago I did see a video/TV program regarding a trucker that was considered innocent because the fatal accident was caused by the steering arm breaking off on his vehicle due to a manufacturing flaw similar to that drill bit. (sorry I don't have any link, but it doesn't matter, the knowledge matters)
I had (seemingly) the exact same thing happen with a Norseman moly alloy drill. Exact same correspondence where they told me not to pre drill. News to me. Worked every other time.
If you have the spindle torque to do it, go right to size in soft materials . I routinely drill 2” holes in aluminum without predrill. Also, the split points are great for eliminating step drilling, plus it’s time consuming. Hog material whenever machine and stock allows it.
I love your videos. I usually learn something and enjoy trying some of the stuff you do. I've got to say not all videos are for everyone. I've been using this one to help fall asleep the last couple of nights.
The darker broke area - as you said with the ductile failure - that is not really consistent with this cracking during manufacturing but the drill breaking under stress during drilling. When the drill is under a lot of stress like enlarging a hole then when the a ductile failure occurs all the build up tension will be released in the form of heat on the fault interface. that can be a couple hundred degrees hot. Had an auger-bit fail on me spectacularly. The cutting edge, the flutes, the entire outside of the drill was cool to the touch, yet the new broken surface was hot enough to burn me.
Great stuff, I have learned a lot from your channel over the last few months I found it. The findings from the microscope are beyond my comprehension, but it is obvious from the discoloration and the soldering magnification that the drill was already cracked during manufacturing. I am surprised that it didn't break as soon as the point hit the material. As far a not enlarging an existing hole, I mean come on, we all do that and seems like a CYA response from the manufacture. I like how you just represent the facts and not blast the manufacture, this could happen to any manufacture, things happen.
Nice to know where to look if something is broken. The centre of the drill is pushing the metal away, so forms a resitance to the drill, preventing that drill is digging into the metal. You see this also happen if drill through a metal sheet, as soon the centre point is through the metal it will grab the metall because there is no counter force any more and the backslash of your drill press will make it worse. So on soft metals it is better not to pre-drill with a smaller drill. But in your case, just a bad drill in on a bad day.
Hi, buddy, nice to meet you. I sometimes find it a little strange for a person to get interest in so small and peculiar aspects of how things are inside and how they work to the point of disassembling them to their last parts or cutting them open when they are somehow sealed. Listening to your video opening speech I was able to realize that there are souls around the world which are just like mine and this is really cool. I have this small backyard office in which I spend most of my free time disassembling, trying to fix , building , changing and trying to understand most things that catch my attention for the most varied reazons. By the way, I once had similar considerations over a broken drill bit and came to about the same conclusions you did: it was previously shattered.
James, thanks for making the video you really made my night. I appreciate your curiosity in finding out the root cause I've always went a step further to figure out how something had failed. One thing I do to reduce the risk of a drill failure is to put a lot of drag on the tail stock or mill quill using the lock, keeps the drill from jumping into the material from any backlash.
im the same way about learning things, I am always eager to learn try and fail just to learn more ... and no I predrill my pre drill hole (not always) but I have heard "start small and work your way up" from just about everyone who has ever drilled something, especially gummy stuff like arlumuiurm
![เปิดบ้าน พี่ตูน Bodyslam หลังใหม่คนแรก ที่ภูเก็ต l [Nickynachat]](http://i.ytimg.com/vi/flFwcmyDQSk/mqdefault.jpg)
A quick tip for anyone that reads this... when you try to do failure analysis like this, don't EVER put the two broken pieces of metal back together. This changes the metal failure surfaces and can hurt our ability to find answers.
I write software for exactly this SEM. It always amazes me what can be done with those machines (I'm SWE, not a physicist). And trust me, this is the most basic type of analysis you can do in them. I have seen people heating golden nanoparticles to 700 C and observing how they started to jiggle. All while seeing individual atoms. I have also seen people micro-machining a few-nanometer-wide lamellas which are then analyzed in even crazier machines (transmission electron microscopes).
Aircraft mechanic of 8+ years. Drilled hundreds of thousands of holes in steel, aluminum, stainless, and composite. With the exception of a few specific drill processes, best shop practice is to step up in drill bit sizes by specific increments depending on material, thickness, and stack-up. I've witnessed very few of the drill bit failures you experienced with this drill bit and can say, with 100% certainty, it is a manufacturing defect. We've gone so far as to purge all inventory of bits from specific manufacturers, with similar manufacture date and heat treat lot numbers, that have exhibited failures like this due to the injuries sustained by mechanics.
It's always nice to dive deeper into these different topics! Keep up the great work!
I bet. If you're working on aircraft, a small problem with a tool can get very expensive very quickly.
What can you do with this information? Hey you are american... just put a legal claim for some millions, 😆
@@jorgeo4483 They just get sent back and replaced with a new batch, and then the manufacturer has to dispose of them. My bet is that they split during the twisting process, as blanks with a round shank and flat end are twisted to make the spiral, then are then rough ground, then heat treated and finally finish ground, with the final process being the final heat treating or coating. Either a batch of alloy that was too cold, or was not mixed properly, or was cooled down too rapidly in the forging process, led to the initial defect there that is where the failure started when it broke, and this first went to the tip when it was being twisted, and stayed there all the way.
This bit was doomed to fail anyway, that split was bound to open up sooner or later, the forces on it made it split, irrespective of it enlarging a hole, or drill into the block from the beginning, that force was applied to the tip in the same manner.
I could not agree with you more. Indeed, my favorite sets of drills are pilot bits (mine are made by DeWalt) which have an integrated smaller bit that starts the hole followed by the larger bit. Whoever responded to James was full of crap. This bit was flawed.
@@flingshotlife Easy, just do not buy the cheap horor fraught bits unless you are prepared to use once. I have had good results using bits from tool suppliers, and Dormer makes good low cost bits. Just do not bother buying cheap, especially in sets unless they come from a tool supplier, or are branded from Dormer, Bosch, Hikoki, or any of the larger tool manufacturers, who have them made to their spec. Anything that comes as cheap sets, especially with a badge just placed on the box, is not the best, some are not even hardened steel at all, just ordinary steel ground to shape, because that is easier, and they twist straight the first time you use them.
I worked in a 7-acre Fortune 500 machining plant that heat treated 24/7. I was the QC manager, and failure analysis of this type (sometimes including our SEM) was an almost daily occurrence. I've prayed over many pictures of metal microstructure! Thanks for bringing back memories James!
Agree with the pre-existing fracture. That clearly occurred during the manufacturing process. The secondary fracture does not appear to have failed all at once. Your low mag optical photos at around 3:45 to 4:00 show evidence of fingernail-shaped “beach marks”. That is clear evidence of a fatigue failure. As external load is placed on the material, the fracture grows one cycle, the distance between consecutive beach marks. That says there must have been a repeated application of load that advanced the fracture surface the distance between the beach marks. Since that distance appears to be relatively coarse, the load could come from the advancement of drill via the tail stock. You twist the handle, stop for a fraction, then advance it applying more load (speculation on my part having bored many holes on a small hobby lathe.) The cross-section of good material keeps becoming reduced as the fatigue crack grows. Eventually the tendril of remaining material fails to support the external load (stress) and the material fails in final fast fracture, evidenced by the cup and cone appearance by secondary electron image of that last photograph you showed where you could see the little round inclusions sitting within the base of the cone. Those inclusions served as nucleating sites for the final fast fracture.
I am a metallurgist, MS degree, with 25 years of performing failure analysis on a wide range of materials including steels, titanium, niobium, zirconium, and other structures. If you can get back on the SEM and get a set of low magnification secondary electron images, say 10 to 25X I think you will readily see what I’m talking about.
The one question I have about this theory is: Why did the fatigue crack meet up smoothly with the pre-existing manufacturer-error crack? I wouldn't expect that to happen unless they propagated from the same exact stress tensors.
@@avialexander the fatigue portion of the fracture took off from the preexisting fracture. There is an extremely high stress field at the tip of the preexisting crack….one that can easily exceed the yield strength of the material. The sharper the notch at the crack tip the more concentrated the stress field. This can be verified in that the tips of the thumbnails point in the direction of the crack elongation. This is not so much a theory as a well known observation of failure mechanics. In effect the failure had three distinct modes. The preexisting brittle fracture, the low cycle fatigue portion, and then the final ductile fast fracture that looked to be mostly in tension (the cup and cones were circular, not elongated as in shear. It’s like reading horse tracks or animal tracks in the old West.
@@Zircon10 I believe you may be mistaken about the beach marks. I'm not an expert, or even certified or anything, but they wouldn't occur on the trailing edge of a fracture, right? That's the fast fracture area. Also, normally we're used to seeing them on relatively shallowly rounded surfaces, like round fatigue test bars. But this was a very sharp corner, and you can see that the curvature of the beach marks becomes much more shallow farther away from the corner, indicating to me that the fracture was growing away from that edge, not towards it. Welcome your insight here.
Alex, the fatigue beach marks certainly can occur on the trailing edge of a fracture, especially if the mode of the fracture is totally different. The original fracture emanating from the split point of the drill has all the watermarks of a brittle fracture that may have occurred during heat treatment or was exacerbated by thermal stresses of heat treatment. The heat tinting of the surface of that fracture roughly matches that of the outside surfaces of the drill bit and likely occurred during tempering as that "straw" color is associated with low temperature oxidation.
There are large beach marks near the core of the drill that have quite wide spacing. The beach marks you are talking about near the surface are the result of high surface stresses prior to failure. There is little cross-section to support the material at this point and it is not unusual to see secondary fatigue cracks, especially emanating from the surface.
I hate to tell you this, but your interpretation is incorrect. The fracture started out as a manufacturing defect, progressed down the length of the bit in low cycle fatigue, and eventually failed in a ductile fast fracture when insufficient material was present for the load applied.
Enlarging holes is common. I do find if you don't allow the next larger size bit to load up at least half of it's point width, especially in soft material like aluminum, the bit is likely to dig, then grab and break. For example I wouldn't go from 3/8" to 1/2", but would go from 1/4" to 1/2". If you have to go up in size a little where the bit is likely to grab, then a really light feed will help keep it from digging.
Not only that, but one is wasting time if the increase in size is too small. The previous drill bit in every step of the sequence should be just slightly larger in diameter than the chisel point of the larger drill. Going in increments that are unnecessarily small at best only increases the number of operations to no good end, thus wasting time. There is a huge drop in cutting force as soon as the hole is increased beyond the length of the chisel point. Beyond that, the reduction in force is not that great, and as you properly point out, gouging and grabbing get more and more likely. This was not the case here, though. This was just a drill bit that was already cracked.
I don't think it was... Hard drills like this have no forgiveness for the sudden twisting of getting caught up in a hole like this with aluminum. Aluminum heats up and the hole contracts if your not drilling properly and his lathe basically grabbed that drill and twisted it to death from 0 to 60 in under a millisecond. If he used an HSS drill it would bend and not break.
This is something that works really well for me, at some point in time I heard a general rule of thumb for pre-drillng, the starting bit should be around 1/3rd the diameter of your desired size.
Too small of an increase will in essence cause the bit to thread itself into the material and quickly stall or break.
This sort of comment is really useful, I definitely just learned that I've been trying too hard to go "little by little". Thanks!
I love the comments about just being curious and figuring things out on your own. We need more like you in the world
For many of us this is the way. My creed is that if you don't learn something new everyday you are missing out on life. You must drink deep of the waters of life, else why live.
TURBOCAM’s TX1 treatment would improve the survivability of the tool 👍
Machinist are the last people you should ever share an opinion with. If you lightly suggest that they are doing something incorrectly, they will become very unstable. Nothing is more fragile than the heart of a machinist. BTW a own multi axis CNC machines.
@@wannabecarguy my company employs the country’s best machinists. Great people. Morally and spiritually stable. Excellent skills and craftsmanship. I’m happy to be a servant of them. Thank you TURBOCAM.
As a former field service engineer for an electron microscope company, I'm very impressed with your accurate and concise explanation of how an SEM works. I really enjoyed the video.
I have NEVER said I need an electron microscope. I'm happy you said it.
I have never said I NEED one. But I have often said I WANT one.
Hi James. Very educational video!! As a young graduate engineer about 50 years ago I was faced with a problem on a bridge job site. The steel girders were manufactured to old plans however the new transverse stressing bars would not fit through the holes in the beam web. The beams would have been equivalent to a Gr250 or Gr350. The problem was compounded as half the bridge girders had been placed in position high up over the creek bed. From memory, the holes needed to be enlarged from 1.5" to 1.625". The holes had to be drilled as the use of oxy/acetylene enlarged holes was prohibited. The contractor wanted a lot of money to crane down to the ground the already installed beams. A normally ground 1.625" twist drill would probably last one hole or bind and stall the drill. The solution was simle. I just ground the drill's cutting edge to square up the cutting edge to a near neutral front relief angle. This worked a treat. Having a near neutral front relief angle meant that the drill would not grab the work.
good thinking. This is similar to what you would do if you had a dedicated set of drills for brass and other grabby materials.
You can take a really long scan where you make separate images for each element. It can show where in the sample each element is present, and you can often get an idea of the composition of individual grains.
I believe this is called EDS. We use this in mining a lot to look at ores so we can figure out how to extract the desired minerals.
EDS is the X-ray spectroscopy in general, “EDS Mapping” refers to the colorful overlays showing the location of different elements in the field of view like you’re describing. Most systems do both.
@@alexdrockhound9497 It's either EDS or EELS. Depends exactly what you want to look for.
I spent a few years in a machine shop that's been in business for around 60 years. It was pretty standard known not to enlarge holes with a drill if you have any other option to enlarge the hole. I was taught the tip grabbing into the material does a lot to hold the drill centered. That when a hole is enlarged, it can cause vibration in the drill which can uncenter the drill causing a higher force the flutes can't handle
Right, if you jam one side of the drill against metal and not that v in the center then ... surprise! It will fail on the side of the drill like this. It's fine to do but I don't know that it would be best practice, everything in me screams you gotta bore that sucker out with a boring bar. I think best practice is you make one hole and bore it out, making two with a drill is misguided but also who cares it works often enough and breakage is a part of business
In the production CNC world I never spot or pilot dill holes. If you are using crankshaft, four facet or most any variation of NC point it isn't necessary. Sumocham, KM Go drills, Mits or Sandvik will prefer you drill the biggest diameter first in the case of stepped holes. Most manual machines don't have the thrust, spindle speeds, HP or the necessary guarding to run at mfg recommended drill speed and feeds. Running manual machines, what you did was prefectly fine. The drill was defective. Even the best drill manufacturer gets a bum drill from time to time. I had a run of a dozen 1/4 - 20 Taps from a highly reputable mfg blow up on every hole during a turnkey one time, switched brands and tapped hundreds more before the gage started getting tight. Stuff happens.
Love my Nachis 😊
Well, yeah. CNC is very different in a lot of ways than manual machining. For one thing, a CNC machine doesn't get tired or run down when pushed close to its rated limit.
I have always been taught to not pre-drill except on big drills where you need enough to accept the chisel edge and that is to reduce the pressure it takes to shove that through the steel. The 135 degree split point are made to not wander with the grind and the thin web. In soft material like aluminum or plastic the drill is more likely to "thread" its self in. I have had the MT4 mounted chuck get yanked from my spindle with drilling Delrin that has an existing hole. I look for core drills or "Dreamers" for that if I have them (that is rare). Cool stuff man, I appreciate it!
I've experienced the same thing in UHMW, Teflon, and Nylon. I switched to a hand ground HSS boring tool in those situations. Always funny to see the looks of people when the part pulls outta the chuck too.😂
Amazing electron microscope videos can ironically be found at a channel called Breaking Taps
Great engineer as well with awesome explanations
Yeah. He's great.
Ah, micro-cracks: those horrid things that are almost never found before it's too late. Seeing that one can silently and stealthily sit in a drill through use in multiple projects before becoming a failure point makes me sympathize with aircraft and bridge engineers all the more.
I had an identical failure with a DrillHog drill. In my case the flute broke off as soon as the drill hit the material. They did warranty it. It looked exactly like your failure, with the old and new broken areas clearly different. No doubt in my mind it's an artifact of the manufacturing process. Nothing is perfect, and I've gotten good service from all the rest of the drills I've bought from them.
It could be a common failure and the best QA is to ship them anyway and honor the warranty for the ones that they couldn't reasonably QA in house. I.E. You do the QA.
We use cobalt to drill the initial pilot hole, then switch to a conventional bit for opening up the diameter. What our machinists have found is that the overbore/opening up procedure adds excessive unsupported shoulder loads to the hardened bits causing breakage. Using softer HSS only requires the shoulders to be sharp, and the softer steel can absorb the micro vibrations with no issues. And the guys actually have contests to see who can sharpen their bit shoulders the finest. Much easier to touch up shoulders than pointed tips. Just our two cents from the guys here at the shop.
I actually came to the complete opposite conclusion! If you look at the crack at the rearward side, where it broke at the cutting edge, you'll see "beach marks." These are characteristic of a fatigue fracture initiation site, and that was my first clue. I was suspicious of the idea that the bit could be cracked from the factory so severely down the middle and not chatter immensely or break early. Another characteristic of fatigue fracture is striations in the "fast fracture" portion of the break, when the material finally gives way, and we see that in the tip-ward part of the fracture. One more thing: brittle vs. ductile fracture release energy in very different ways, and I think that may explain the oxidation. A brittle fracture releases energy as vibrations, and those dissipate throughout the metal as the sound is absorbed into the bulk material and other objects it's connected to. However, ductile fracture releases most of its energy into the material that is actively being stretched! That means, your ductile fracture surface was going to be very hot when it opened up and got exposed to air, which I think explains the oxidation (in addition to a lot more surface area to react over). And finally, the location of the transition between the colors. It's right at the point where the web of the drill starts, the point at which the cross-sectional distance across the fracture stops decreasing. I'm pretty sure this is due to the transition in stress direction from a mostly pure head-on shear crack to a side-loaded torsioned crack, and that also explains why it did not crack down the middle, but instead went to one side of the center of the torsional axis.
Take this all with a grain of salt, I'm just a mechanical engineer who got really into materials in college, not someone who does this for a living or knows my stuff.
P.S. @Zircon10 has a good explanation for why I'm wrong about this, and is actually a professional.
I don't think it was a full-on fracture coming from the factory. For one thing, that might have been pretty visible before the separation occurred. Rather, I suspect it was a micro-fracture, basically an incomplete fracture that produced a weakened area in the bit that eventually separated under heat and stress. Your explanation of the Oxygen contamination of the fracture is possible, but I suspect incorrect. Oxidation takes time, and the environment of a ductile fracture is not going to be highly uniform nor likely to be comparable to the environment during heat treating. The fact the concentration of the O2 in the fracture is virtually identical to that of the exterior of the bit suggests to me its presence was due to the heat treat process, rather than to the ductile deformation. I certainly cannot say with any sort of authority you are incorrect, but I suspect you may be. Either way, however, it is perfectly clear this bit was definitely flawed. I have broken a small number - very small, I am happy to say - of small drill bits in Aluminum by inadvertently allowing the bit to clog. Looking at the video, I am quite confident the bit was not clogged. Look at the chip coming out of the Aluminum. That hole is not clogged. Furthermore, I have *NEVER* broken a bit anywhere nearly this large in any medium whatsoever, and certainly not when a properly sized pilot hole is employed.
This is what I tried to explain in his last video but not as technical as you. Great job. I've seen this happen myself with a lathe. People will tell him they drill holes all day and have never seen this but I'll bet they drill vertical holes. Gravity, his taper, drill chuck, and the sudden load change from the tip of his drill to the edge getting caught in his hole have a lot to do with this. In his last video, it's clear that his tail stock was hanging out way too far and the pressure on the tip of the drill was too much causing the hole setup to flex... This flexing made the flute of the drill get caught on the inside of his hole and all the inertia of the spinning lathe chuck just snapped that hard drill (which would not have happened with an HSS soft drill) At the same time you could see the drill and chuck get pulled off the taper just a tinny bit. James knows his stuff but just like most machinists I know don't like to admit to being wrong about something unless you can repeat it for them. This could be done with his setup over and over...
@@Jeralddoerr What are your qualifications to make this statement?
@@Jeralddoerr Uh, nope. I have been machining for nearly 40 years, and done many thousands of horizontal holes. Except when drilling small holes, I always drill a pilot, and then step up to larger and larger drills.
@@williamsanders6092 breaking a drill or two myself in 20 years of home machining on my lathe EXACTLY like this! Also, I worked at a company that sold tooling for 6 years... That's all..
This deep-dive nearly pegged the Nerd-O-Meter. Love it! Thanks, James, and congratulations on reaching 100K. Well earned. 👍
What do you mean, "Nearly"? We Engineers can peg the Nerd-O-Meter by just looking at it!
Looking forward to half the stuff in the shop being imaged in a SEM because of the potential sponsorship deal going through. Also thanks to you and your friend for teaming up to make this cool video. Friends are great. Friends with cool tools are *really* great.
Shoutout to Drill Hog's customer service. Just started buying that brand and its good to know they take care of their customers.
I plan on buying bits from Drill Hog after this video!
Thank you for sending me down the rabbit hole of wanting to understanding the difference between an Autodidact and a Perdocent!
Neerd-sniped again...
This was a great video. Failure analysis is such a fun road to go down. As a retired rocket scientist I have had the opportunity to be involved in a number of Failure Analyses, some with catastrophic (and adrenaline inducing) events. My favorite event was watching ceramic catch on fire. Cheers!
James, some 50 years ago I got my degree in material science way back in Sheffield, UK and those semi circular bands in the failure pictures, to me, look exactly like the classic fatigue type failure. Normally fatigue takes many cycles to show evidence but with that material being so brittle each rotation of the bit whilst cutting would add a torque to propagate the crack some more. I agree that the dark area was probably formed at manufacture as the rounded smooth rather than angular structure of the crack surface, to me, indicates some elevated temperature or carburising process. Are the drill bits quenched in an oil bath as part of the heat treatment? Alloys of steel can be quite complex and getting the composition just right for the intended purpose is akin to the black art of alchemy; in general the interstitial nodules are there to pin the dislocations and increase the resistance to deformation but the size and distribution of them is critical and usually requires some complex heat treatment process to get it just right. I n summation I think you got it just about right and the drill supplier should be contacting the manufacturer regarding their below par quality control.
Yeah, I was thinking fatigue initially also, based on the ridges, but it's so brittle...
It’s pretty obvious it’s a fatigue failure but there isn’t enough information about the drill’s life. How many cycles had it done or was this the first use? Was it dropped? I see the classic fatigue fracture line running along the drill axis that are coming from the tip. That rules out the whole dark area being a factory defect although I couldn’t rule one out at the tip. It had to work in torsion to create those fatigue lines of those colours as the post fracture oxidation needs time to set in. I do like your line of questioning James with the colour change but you simply overlooked some evidence that is significant mate, and that changes the whole line of investigation. BTW I’m an Aussie mechanical engineer with endless curiosity which is how I ended up studying after 10 years as a soldier. I worked mainly on guided and unguided things that go boom, but also armour and tier 1 motorsports. So if you go back to the footage and see what looks like rows of sand dunes running along the length of the drill in the older fracture area, each of those is a fatigue fracture expanding one load cycle at a time. If your scope could get an oblique angle with a lower light angle it should pop out. I’d hazard a SWAG that you used it and expanded the fatigue failure, put it away and then the next time you used it a few days later it failed. I could be wrong and that’s okay too but I have seen similar and was lucky enough to study failure analysis and non-destructive testing with the folks considered the best in the game in Oz. Still doesn’t mean I’m right 😂
any drill bit with a reduced relief (back cut) on the trailing edge is not designed for enlarging holes.. at least that is what I was taught and my personal experience has proven it to me as well.. they always seem to shatter
Well, it depends upon the material being worked, but I don't think that was a reduced relief drill bit. What's more, as he pointed out, in that situation, the bit shatters (as you say). I have never seen a bit split along its spiral like that.
When I was in high-school there was a hiproduction machine shop across the street I walked over to and apprenticed ran screw machines went threw alot of drills we had six 1/2 cobalt drills from Enco now MSC did same thing split like that looked just like that! They sent us new ones hell they chatterd in the hole they were split also switched away from that bit for a while problem went away orderd them again never had a issue again 🤷♂️
Drilling aluminium is probably one of the lowest loading scenarios though... 🤔
I bleave it's quality control of a product . There a big difference between work load stress- chip weld feed rate ect think its plan and simple defective.
@@peterfitzpatrick7032 Well, no. First of all, most wood types and most plastics are softer, and there are quite a few softer metals. Of course the softness of the material is not the only consideration for loading, but I doubt anyone has ever broken a drill bit due to excess torque when drilling balsa wood.
Thanks for summarizing your learnings so neatly and cleanly. I learned a lot from this!
I work with SEM, FIB, TEM, and STEM imaging systems for work doing failure analysis. I also use EDS and EELS analysis for material composition analysis. This was a very fun video to watch. If your friend has access to a STEM or TEM ask them to to an insitu lift out at the transition and then image it in a STEM or TEM and perform ELLS or EDS on it looking for oxidation or a change in crystalline structure. Some of the pulling your seeing is pre stress failing due to heat and some is from the time a failure would wager too. Would be interesting to see the material analysis report.
"Would be interesting to see the material analysis report." - I'm glad I'm not the only one that would love to go that far into a broken drill bit.
@@Dreddip I resemble that remark! Yes, it is definitely an academic excercise.
Wouldn't the drill sample be far too thick to do TEM or EELS on? I thought the sample thickness needs to be less than a micron for the electrons to penetrate.
@@cameronmcguire5025 that’s the purpose of the insitu lift out, you pull a small section out using a FIB and then thin it to electron transparency for imaging and analysis.
@@Human_OU812 oh okay, I'm not too familiar with TEM and FIB, I'm a graduate student studying studying the use of EXAFS and XANES and I haven't come across those terms you're using before. I'll have to look into that.
Very nicely done. A few things to remember when doing SEM/EDS analysis. First the secondary/backscattered image is a surface effect and backscattered is average Z (atomic number dependent), so darker is lower, brighter is higher Z. So backscattered is good for quick average Z grouping. EDS however is volumetric, that is the x-rays come from the excitation volume below the surface. Classic tear drop effect. The electron acceleration voltage determines how far into the sample. So you can play games with how far below the surface by adjusting the acceleration voltage. Of course, the lower you go in voltage, the harder it becomes to identify elements from the lack of excitation lines. Typical acceleration is 1.5x the lines of interest. Also doing EDS on a non-flat surface become tricky as the x-ray takeoff angle (to EDS detector) varies and the math becomes impossible to calc accurate weight percent of elements. Flat, polished surfaces only for serious EDS analysis. At one time we had two SEMs with EDS detectors in house. Lots of fun. I miss them.
Like you mention, you have to be careful about assuming the height of the histogram peak is proportional to the amount of the element present. The peaks represent number of X-rays received which is a complex result of many factors. Comparing Cobalt peak in one sample location relative to another location is generally safer. Trying to compare e.g. Cobalt peak height to Iron peak height at the same location has much less meaning. Sample prep and software tools exist to try and estimate relative proportions more accurately, but in my experience this was very uncommon in casual analyses.
As someone else mentioned, the window on these detectors frequently block or seriously attenuate X-rays from lighter elements like Carbon and Oxygen so those peaks often aren’t super accurate.
From my limited experience (as a co-op for GE Aviation doing metallographic analysis, materials science background), I'm only 3 minutes in and your interpretation seems right to me. The bright silvery failed surface is what failed in tensile overload, while the oxidized surface has obviously seen life. This is actually how some aerospace investigations are evaluated (you can sometimes count the number of cycles a failed part has seen based on the different oxidation state colors (forms a series of color gradient bands, a different color for each # of 'cycles' that part has seen). Obviously the more oxidized a surface is the more time it's been epxosed to the elements or whatever environment it operates in. This video brings back memories of interepreting LCF (low cycle fatigue), HCF (high cycle fatigue), and basic metallographic failure analysis, loving it! Will continue to dig in!
Since it seems you have ready access to an electron microscope, you could do EDS on any specific points of interest and determine what elements are present at that location (ie, when you mentioned the precipitates (nodules) in the surface that you expected were tungsten, if you did EDS on one of them you could confirm (ask whoever does your electron spectroscopy, they'll know). You could also confirm the oxide presence in the exposed/previously cracked surface using EDS, finding a lot of oxygen and the other elements present in the the composition. Compare that to an EDS of the tensile overloaded.
James,I have had 2 very similar failures with 8% Cobalt HSS drill bits in the past. In both instances you could clearly see a flaw had existed before the drill split apart with the same different colour and grain structure features as seen on your broken drill. It just happens on rare occasions that a drill bit has a flaw in the material stock or a flaw occurs due to some fault in the heat treating process and it gets missed by quality control. The investigation with the electron microscope was fascinating.
First of all, thank you for this very informative video, and all the others before! I was taught that pre-drilling is done to avoid high axial loads on the drill(-ling machine), which come from the unfavorable geometry of the drill in the central area, where it only displaces the material, rather than cutting. Even with the split point grind, the geometry in the web area of the drill bit isn't ideal. The recommendation is to pre-drill with about the size of the cross width of the web, or about 20% to 30% of the bigger drills diameter. Usually holes under 8 or 10 mm don't need to be predrilled (would require a tiny 2mm to 3mm pre-hole).
I was taught that IDEALY the pilot drill size should be the dia. of the center web of the finish size drill. That's fine if you have a high horsepower machine, but most of us don't so we need to step drill. Also: I have broken bits while step drilling on the drill press but never the lathe. I believe this is because with lathe drilling the feed is controlled by the tailstock feed screw, while on the drill press it's your hand on the handwheel, so if the drill grabs it will be pulled away from you.
You can try drilling to the clearance size of a small boring bar and enlarging from there. Should be faster.
@@rockmonkey37 That's the only thing that seems to work in plastics that have been pre-drilled or need through drilled. Will pull the part out of the chuck when it grabs (when it grabs, not if)
honestly i enlarge holes almost daily on work from 14.2mm to 22mm so 4.1mm per side and i never had a drillbit fail on me like in the video.. and i run it at insane feedrate mind you..
350rpm with 350mm/min feedrate (1mm per revolution). (normal Hss drillbit aswell..) oh and 50mm deep, normally like 60 holes per plate.. and the drill withstands all 60 holes.. ( i do have to regrind it after a plate due to excessive wear, because of the feedrate tho..)
SO in my opinion it does not matter if you enlargen a hole or not, it shouldn't fail like in the video period.
@@FireGodSpeed That depends on how "grabby" the material is, and the rigidity of the drill press/lathe.
That is one common failure mode, and yes, it is more likely in the drill press than the lathe.
Just noticed 100K finally, you deserve 1M + and more. I really enjoy your down to earth approach, you’re personal deep dives and sharing your insight while doing so.
In school I was definitely taught to not enlarge holes with drills. At most, a pilot drill avoid be the diameter of the chisel tip of the large drill.
Obviously, that's a sort of "horsepower elitism" there. Smaller hobby machines can't drive big drills outright. But yes, enlarging definitely concentrates the stress on the outer edge of the drill, and can cause extra wear and failure. And it can cause drills to bite and self-feed, which also increases stress.
I think you've proven well that there's something up with the manufacturing of the drill here, but that doesn't also mean that user error isn't a factor.
I think they're 100% doing the right thing replacing the drill, but also pointing out that technique plays a factor.
The fracture surface has "beach marks" which are evidence of metal fatigue. The "beach marks" are the curved lines that start at the edge of the drill and progress towards the center of the drill. Once the fatigue crack is deep enough, the material will fail suddenly. Your analysis is correct in that the drill did originally have a longitudinal crack since there is oxidation on a portion of the separated surface. When the drill was loaded during drilling, the portion of the drill that was separated from the body of the drill was exposed to multiple loading cycles which lead up to the fatigue failure. Again, your analysis is correct, but I did not hear any mention of the fatigue failure that the "beach marks" are evidence of. I am a mechanical engineer with 36 years of automotive experience and have many years of failure analysis experience so the "beach marks" are something I am very familiar with.
I really admire you for being curious and providing the community with the things you make and research! Keep doing this!
I'm a former materials science technician who ran an electronic microscope for several years. I also have a physics degree. Great job explaining, and I fully agree with your conclusions. You just gained a subscriber!
Best part: “What can we do with this information? Nothing.” - the same as 98% of the rabbit-holes I run down myself 😂
We all knew it was a "bad bit" but to break it down with the education on an electron microscope was great! Thanks James. The "call me" at the end was awesome.
I always knew something is missing from my life. Now I know its a scanning electron microscope. Thank you James for showing the way
Dang, must be a pricy drill bit if they were like "yeah I'll replace it and throw in the associated bit we claim you should have used" 🤣 And then you do the hard work of failure analysis for them 😁. Thanks for the very nerdy and excellent look at the drill under the SEM, I really enjoyed the explanations.
Just good customer relations, and also a company that offers a lifetime warranty, not expecting much use, because most of the time a drill bit fails it is due to abuse, or it just wearing out. Here it was definitely a latent defect in the steel, and they probably have had a few of the same batch fail already and been reported.
The only reason to pre-drill or pilot drill a hole is to clear the web. It’s a lot harder to push a drill when you don’t. In my experience the least times you step up in drill sizes before the final, the better. A split point has practically no web at the point so generally they don’t need pre-drilled… so long as you aren’t using a cordless drill.
Very cool analysis! Every machine shop should have an SEM available for this kind of deep-dive! 🙂
Couldn't agree more. Any great tips on how to pick one up without selling my house?
@@Clough42 you should check out Breaking Taps channel and some of his homemade equipment. An autodidact like yourself might get stuck down the rabbit hole though :)
Maybe ask your friend to scratch an carefully dent an pull a wire off inside. Then they might just replace it? Colleges have lots of money. Then pull it out of the dumpster... Or maybe they have and older one in storage?
I did like the video. It was very interesting. Being able to tell what elements are present would be handy. No more mystery metal! I know nothing about SEM but for what it is worth based on what you were saying an showing I agree with your findings. I am going to see if I can get a much higher magnification lens for my old B&L microscope. I suddenly want to see as much as I can. This rabbit hole may get very expensive!
That takes my mind back to the late 60s, I took an industrial Physics course in High School and one of the things overed was Metrology and Metallurgy, we had to test metal samples to the failure point. the samples were metal rods which we stretched until they broke, usually with a snap that sounded like a gun shoot, which made everyone jump.
I know I'm tired because when you said it's an M42 drill my first thought was "that looks way smaller than 42mm".
I have black belt electron scanning microscope degree and PhD / ScD of Drilling and after analyzing your video I can say that this drill is broken.
Thank you.
I worked with Carbide for many years as I was a machine operator in a carbide tool manufacturing plant. I've seen many tools break or come apart such as your sample. Carbide is "sintered". That is, the composites making up carbide are mixed together as a powder and then heated under pressure to create a solid. The gold color on your sample almost certainly means it was fractured AFTER manufacture.This is why, of course, some traces of the coating appear on the fracture. It is sometimes very difficult to see a fracture on a particular tool that would lead to it cracking. Of course, we didn't have the use of a SEM while making tools. We would sometimes drop tools to see if they broke apart if we were having problems with a particular batch of carbide. This tool pictured had a fault from the sintering process before it was ever fluted. We found that certain suppliers of carbide were prone to this problem and therefore we tried not to use them. Certain composites (called grade) of carbide can be in extremely short supply, especially if a particular type tool is specified on the print. Generally speaking; the more harder-acting the carbide tool is, the more expensive its cost.
When I programmed CNCs in the 90’s, we almost never programmed pre-drilling. Only for very large diameter drills. We almost always center drilled and then just plunged in the drill. The advantage of the CNC is of course that you always get the correct cutting and feed speeds.
I agree that expanding existing holes can be a bit hard on the drill but sometimes it is required. Not many home shop machines have the power to push a bigger bit without a pilot.
There are rare and expensive 3- and 4-flute "core drills" for that, although when I asked Somta about them they said, "they start at 14mm and they're morse taper shank only".
I think it's the difference between a pilot hole which is on the order of the drills core in size and taking a 20mm drill through a 17mm hole
huh..?? I work in a foundry for the mold department, we have plates out of normal soft steel (S253JR) and we predrill the holes on the CNC and then turn the plate over and enlarge the holes on a drillpress from 14.2mm to 22mm diameter so 4.1mm per side, depth is 50mm deep, there are roughly 60 holes per plate (2plates needed, top and bottom) and i normally run the drill with like 350RPM and 1mm/revolution so 350mm/minute feedrate. Thats insanely fast if you look at it in person. You know what never happend? that the drill split like in the video.
i can do 1 plate before i have to sharpen the drillbit again. (duo to the excessive wear because of the high feedrate) And thats with a normal HSS drillbit mind you.
Absolutely TRUE! However, you should use a slow feed rate on the drill to prevent grabbing. Large increments are easier on the drill and work fine. The goal is to relieve the tip, which has awful cutting geometry.
@@FireGodSpeed Aluminum is probably more grabby. Do you use fluid? Also the drill geometry matters. I bet you are just more experienced as well.
Great video! I am a PhD student using scanning/transmission electron microscopy to study ceramic crystal structures, and I thought your explanation was very thorough and concise. One thing I thought I would mention is that EDS/EDX (Energy Dispersive X-ray Spectroscopy) for elemental analysis is usually only semi-quantitative at best, at least without a reference sample. Also, unless you have a very specialized detector, the technique is inaccurate for detecting elements below an atomic number of ~11 (this is due to the low energy of the characteristic x-rays these elements produce).
I suspect that the high carbon (atomic number 6) presence in this sample is not only the carbon present in the alloy, but also carbon contamination from the environment/touching it with your bare hands. You can alleviate some of this contamination by plasma cleaning the surface prior to loading, but environmental contamination is always going to be present to some degree.
Oxygen is also
The main thing a degree teaches you is how to learn, often the knowledge you gain is of limited use but the ability to research and learn lasts forever.
As for your analysis I'd say that was pretty good, I'm not an expert but I've done some SEM analysis in my undergrad days and everything you say seems right. My PhD was in a different area of physics, I really like your thirst for knowledge and the fact you have a friend with access to an SEM.
Thank you for an interesting and thought provoking video! I find that the most significant problem with the autodidactic approach is that there simply are not enough hours in each day, particularly when you have to exchange a portion of those hours in exchange for money. 🙂
Enlarging existing holes is normal and should not lead to failure of that sort. That said, ideally the right tool for the job is a "core drill" (not to be confused with the other type of "core drill"!) which has three flutes and an extra thick web. You get better roundness and even less chance of breakage.
Thanks for the detailed breakdown. Very much appreciated James!
That is the weirdest drill failure I've ever seen. Thanks for exploring it to this level. Very cool!
Just a 👍from me and a subscription. As a retired engineer, videos like this keep my geek alive.
As a Knifesmith, I've drilled many holes in steel, never seen a bit break like that, however, after doing snap tests on many steels, I noticed straight away the difference in grain growth in the broken section. 👍🍻🇿🇦
Hi James, did you think about breaking that tip of the drill in another place to see if the whole tip has a different color and then it can be attributed to the heat treatment? It should be a simple whack with a hammer and see if it has the same color... right?
While it would be a fairly rudimentary test at this point, if you happen to have a set of Rockwall hardness files, I'd be curious to see if the off-colored areas test significantly different to each other. The surface of hardened tools, especially with a topically coated treatment, should be at least a grade higher than its core. That's not indicative of a manufacturing defect by itself as stress fatigues can certainly affect a steel or alloy's hardness up to the moment of failure (and/or induce it), but a coating applied to a tool that either failed heat treat (or in specialized cases, cryo treat) would show up further away from the failure site if you're up for a full post-mortem.
Excellent video, James!
I hope an SEM manufacturing company watches this video and works out a sponsorship deal with you.
I think from now on the right thing to do is to X-ray your drills before use so you can avoid potential headaches in the future.
Oh, such memories! But also, I share 100% the lifetime interest on all kinds of odd topics. Sort of everything between ground and sky (including chemistry, metallurgy and astronomy). All of those far away from my professional education. However, at one point I participated in troubleshooting of a paper machine dryer cylinder with a boss, who was even more skilled on various strange things than I was. He decided we needed to get photos of the cylinder surface morphology, using SEM. As we could not take the 16 feet diameter cylinder to a SEM machine, we made imprints of certain locations of the cylinder using some plastic. The SEM operators plated our imprints with metal and then scanned it. Unlike optical microscope, the SEM process had a marvelous depth of field, so the imprint piece could be tilted at will and everything still remained in focus. Marvelous pictures! Your story also relates to another past experience of mine. At a time I was presented with a challenge of an unsteady GTAW (TIG) welding arc. Turned out to be a split tungsten electrode. It also was a manufacturing issue -- inadequate bonding of the powder in the sintering process. That memory immediately flashed in my mind when I saw the split of your drill bit.
I used to work at a Test House with a SEM. I was told that when things break NEVER try to put the parts back together. It's better to leave them apart as any further contact could mask the reason for the failure.
Interesting video and information. In my life before retirement, I was involved with Overhead crane maintenance. A large part of these cranes consumable parts are the wire rope that is used as part of the hoisting of the load. One of my many training materials the different types of failures of the steel wire when a wire rope failed prematurely. What was interesting in the literature was the electron microscope example photos that showed the difference in the wire failures. With that you could examine and determine most of the time the root cause of failure by just cleaning and evaluating the break with a simple magnifying glass. Great stuff. In all the years that I drilled holes and observed holes drilled, I never seen a drill bit fail that way. When you showed the failed bit I was curious as you, why it failed.
Thanks for sharing.
That was an a great video sir. Thank you to both you and your friend for the video.
Great video. In my work I have review many failure analysis and have seen similar failures of heat treated parts, one that comes to mined is s large spring. I agree that the darker area was created during the heat treatment (oxidation). I see beach marks in the gray area closer to the end of the oxidized area showing the extension of the cracking caused by the local overloading. this continues while the drill continues to cut until the brittle failure denoted by the course grain and cleaving to the end of the failure.
Interesting. Thanks. Brings
back memories of metallurgy.
Had the opportunity to see an electron microscope used to identify a sample during my apprenticeship many years ago. Very clever tool.
Shop practice != Best practice.
As even many comments here show - many people just do as they have always done. They start at a shop and get told "for XY hole pre-drill with YZ" and afterwards never question that. Drill-manufacturers in general suggest pre-drilling for hole larger than 10mm/ 0.5 inch when working with metal (that is just roughly, depending on the manufacturer, drill, material, feedrate etc ).
had a similar experience when doing my first reflow-soldering back in university. Had my PCB, soldermask, solder and components prepaired, as well as guideline for the solder-profile of the parts and the solder it self. Got to the local electronics-group and started reading through the manual of the reflowoven they had there when one of the seniors came up to me and explained to me how to use the machine and which settings to use..... yeah all wrong: too hot of a starting temperature, too fast rampup, waaayy too hot of a top-temperature, too short on the max temperature, too slow cooldown at first and then basically shock-cooling at the end.
No wonder the guys there kept complaining that they only got bad results and about how much the need a better machine to get better pcbs.....
experiment
EXCELLENT!! It's a crying shame more high school and college science teachers weren't this fun and educational!!
Congrats on crossing over 100k subs! This was a great video for that occasion
I've always been taught pre-drilling was reserved for large drills where feed pressure would be high, too much heating at the web, hard materials, or location was critical and that the pre-drill should be approx the size of the web of the larger drill. My experience tells me the response from Drill Hog is for smaller drills. 🤔
Videos like this is why I follow you. I’m always learning, thank you!
Thank you James, an outstanding explanation of why the failure occurred.
I love the break-down and to have it end with 'so what are we going to do?' "Nothing" I found somewhat humerous considering. Will be looking at your other videos after this!
Congratulations on 100K subs James. Its a great millstone.
Thanks!
Very interesting video.
I almost always drill a pilot hole and have never heard that it could cause a drill to break.
If you look at that broken drill section where the clean break goes into the complete drill I believe you can see the darker section continuing into the rest of the drill. 4.42 in the time stamp.
From my education as an Mechanical Engineering Technician at Purdue University, the dark area at the tip tells me that that area was already cracked. The crack allows oxygen in to that surface and causes that oxidation! Part of my education at am MET included the study of failures, such as this, and that dark color is indicative of a pre-existing crack. The light area is in fact a brittle fracture that happened as you drilled! As to your question about pre-drilling holes ... that is in fact standed machining practice.
You can see the fatigue benchmarks on the fracture surface in the silver colored area. Area shown around 11 minute mark is fatigue crack propagation area. At 11:33 mark, dimpled rupture is noted. Overload fracture. Within cups are carbides. Pre existing defect.
You continue to surprise. That is quite an analysis! This level of metalurgical analysis is not common to home shops! Lots of great comments below, but I have routinely drilled a smaller hole, then a larger one. Aluminum is soft, with good control of the feed, a decent bit should handle the job. It is true, though, that machinists routinely cut aluminum with carbide bits at very high rpm, which would minimize the depth of cut per revolution.
I was taught in the workshop, many years ago, to step up drill sizes to reduce the workload on the bigger bits. I've always done that and never had a bit fail while doing so.
Ok, now I've gotten to the hole enlargement part. I agree with the manufacturer. When I worked under a part time machinist for a short time, he said it was standard practice to use a pilot hole. After watching and doing this myself, I realize the larger bit will tend to grab a self feed too fast if the diameter was close. I suggested to him that the pilot should be no more than one third the full diameter. This keeps the included shoulder angle in play and prevents too fast a feed, while keeping the larger bit tracking true.
Congrats on 100k. Your videos' production values are unequaled!
Most I have known about SEM's now, thanks to you.
I had the same failure about 8 years ago, Sutton 10mm HSS Cobalt drill. Used for the first time and it fell to bits on contact with the job. Unfortunately Sutton Australia didn't even bother replying to my email asking if I could have a replacement. In my email "Upon inspection one can see the outer coating has actually plated the inside of the drill i.e. there was a crack in it during the manufacturing process. " . In retrospect not a coating, just an oxide layer as described in this video. Perhaps HSS Cobalt drills are more prone to cracking during manufacturing than other drill types.
Wow, fantastic work James.
I’ve seen people enlarging holes with drills but I was taught to spot drill and generally not to pre-drill for a drill. I do pre-drill for endmills, though.
Being a hobbyist blacksmith my first thought was that it was a cold shut that possibly formed when they made the grooves by drawing the material through a die and they probably didn't cut enough off the end before moving to the next step.
Excuse my lack of knowledge, but what's a cold shut?
@@vincentguttmann2231 that's when the steel is folded onto itself (kinda like a wrinkle). If it happens at welding heat then it'll just fuse together. But you don't forge at welding heat for a lot of reasons and that means a small cold shut can get into the piece. Once it's there it can be very hard to get rid of, if you can even tell it's there as they can be impossible to see sometimes. Easiest way to get rid of a cold shut is to literally grind/cut the thing out.
A cold shut could definitely have caused this failure. Although, my first instinct thought the blank was put into a hot heat treating oven when the blank's end was too cold (potentially from the thing that grips the blank being too cold and sucking the heat away). If the tip heated up too quickly then it could also cause excess stress and fail in a similar way.
As far as I know, only large drills >1" are forged then twisted. Everything I've seen for smaller drills is ground/cut to shape. I'm pretty sure there are probably some drawing processes used someplace for smaller drills though. There are flute grinding marks present on this drill, but that doesn't mean it wasn't drawn and then finished ground.
What's weird is the crack doesn't appear to originate from a corner or stress riser. Perhaps thermal shock while the tip was being rough ground? I can totally see a cold shut being the origination as you describe.
@@Dreddip You can see the inclusion though, where either there was incomplete mixing in the melt, or a tiny bit of slag that was deep in the original rod.
I don't think drill bits are forged. 'Nice try, though.
I like the analysis, even though it's basically just telling us that there was a manufacturing defect and the solution would be to take a new drill bit and finish the work.
The important lesson here is that this also tells you and everyone else what to watch for in case something serious has happened. That could make a huge difference when it comes to identifying who's responsible for an accident - or not responsible. A few years ago I did see a video/TV program regarding a trucker that was considered innocent because the fatal accident was caused by the steering arm breaking off on his vehicle due to a manufacturing flaw similar to that drill bit. (sorry I don't have any link, but it doesn't matter, the knowledge matters)
I had (seemingly) the exact same thing happen with a Norseman moly alloy drill. Exact same correspondence where they told me not to pre drill. News to me. Worked every other time.
If you have the spindle torque to do it, go right to size in soft materials . I routinely drill 2” holes in aluminum without predrill. Also, the split points are great for eliminating step drilling, plus it’s time consuming. Hog material whenever machine and stock allows it.
I love your videos. I usually learn something and enjoy trying some of the stuff you do. I've got to say not all videos are for everyone. I've been using this one to help fall asleep the last couple of nights.
The darker broke area - as you said with the ductile failure - that is not really consistent with this cracking during manufacturing but the drill breaking under stress during drilling. When the drill is under a lot of stress like enlarging a hole then when the a ductile failure occurs all the build up tension will be released in the form of heat on the fault interface. that can be a couple hundred degrees hot.
Had an auger-bit fail on me spectacularly. The cutting edge, the flutes, the entire outside of the drill was cool to the touch, yet the new broken surface was hot enough to burn me.
Great stuff, I have learned a lot from your channel over the last few months I found it. The findings from the microscope are beyond my comprehension, but it is obvious from the discoloration and the soldering magnification that the drill was already cracked during manufacturing. I am surprised that it didn't break as soon as the point hit the material. As far a not enlarging an existing hole, I mean come on, we all do that and seems like a CYA response from the manufacture. I like how you just represent the facts and not blast the manufacture, this could happen to any manufacture, things happen.
Nice to know where to look if something is broken. The centre of the drill is pushing the metal away, so forms a resitance to the drill, preventing that drill is digging into the metal. You see this also happen if drill through a metal sheet, as soon the centre point is through the metal it will grab the metall because there is no counter force any more and the backslash of your drill press will make it worse. So on soft metals it is better not to pre-drill with a smaller drill. But in your case, just a bad drill in on a bad day.
I’ve always used the same technique to get a hole to size. Larger diameter twist bits don have split points and make drilling more like plowing.
Hi, buddy, nice to meet you.
I sometimes find it a little strange for a person to get interest in so small and peculiar aspects of how things are inside and how they work to the point of disassembling them to their last parts or cutting them open when they are somehow sealed. Listening to your video opening speech I was able to realize that there are souls around the world which are just like mine and this is really cool. I have this small backyard office in which I spend most of my free time disassembling, trying to fix , building , changing and trying to understand most things that catch my attention for the most varied reazons.
By the way, I once had similar considerations over a broken drill bit and came to about the same conclusions you did: it was previously shattered.
James, thanks for making the video you really made my night. I appreciate your curiosity in finding out the root cause I've always went a step further to figure out how something had failed. One thing I do to reduce the risk of a drill failure is to put a lot of drag on the tail stock or mill quill using the lock, keeps the drill from jumping into the material from any backlash.
im the same way about learning things, I am always eager to learn try and fail just to learn more ... and no I predrill my pre drill hole (not always) but I have heard "start small and work your way up" from just about everyone who has ever drilled something, especially gummy stuff like arlumuiurm