Thread Cutting on the Lathe, Part Two - Calculating the Flat Width and Helix Angle
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- เผยแพร่เมื่อ 4 ก.ค. 2024
- In this episode of thread cutting on the lathe we calculate the width of the flat and discuss three different ways to calculate the helix angle.
- แนวปฏิบัติและการใช้ชีวิต
Bravo!!! Never get tired of trig & the science. TH-cam yes, but only to find real people & learn from them before this world loses real talent & truthfulness.
Best lathe threading video series that I have found.
Big respect to you for posting.
Thank YOU!
Thanks for watching!
You're an excellent teacher, Tom. Providing more than one explanation is great at getting to people who learn in different ways, and your presentation style is detailed enough _and_ concise enough -- which is a very tough balance to find.
Thanks!
Everett Wilson
Thanks Everett.
Great video! Excellent teaching skills!
Very cool. Thanks for the easy-to-understand explanation. Looking forward to future videos on other types of bits, or anything else. The drill bit sharpening video was great too.
Great video! You manage to get the idea across in a very clear way.
Thanks
I found this video both clear and very helpful. Thanks.
That's good to hear. Thanks for watching.
Great instructional video for thread cutting. Thanks for sharing!
+Naked Machinist
Thanks for watching!
Thanks, glad you are enjoying the tutorials. I do have one planned on turning and facing tools, but I need to finish the series on thread cutting first, so hang in there, it'll probably happen in the next week or so.
Tom
Thank you, I'm glad you enjoyed the video. I will be doing a video on cutting an Acme thread soon, so stay tuned.
Tom
thank you, sir ! your videos are very useful. it helps me a lot. I'm learning thread now.
Excellent!
great job, unrecognized hero!
I have wanted to reply to this video for some time now and decided to do it.
First I think you are the only person to even discuss helix angle.
Helix angle is very important on bolts as the tread on a bolt is an inclined plain.
The smaller the angle the more clamping force can be applied for a given amount of torque.
In other words low and high gears for bolts.
Thanks for the videos.
Thanks.
That's a very interesting analogy. I'll be sure tuck tuck it away for future reference. :)
Tom
Thanks for the 3-way explanation of helix angle. It made the concept very clear. I have no problem with math and use trig all the time, but I liked the last, graphic example too. It's a pretty simple and fast method and works when you don't have your machinist's manual or calculator handy.
+Lonnie S
Thanks Lonnie. Not everyone is comfortable with math, so I like to offer options. Of course they are still doing math, so don't say anything. :)
Tom
Awesome. Thank you!
Thanks for watching.
good shit Tom thank you
Very nice well done
Thanks for watching
Great teaching!
Thanks....13
Thanks for watching.
As I pointed out in the video, the helix angle is not that critical, especially when cutting V threads. You can use the calculated pitch diameter if you like, but the major diameter is already known and works just as well.
Tom
...continued
Machinery's Handbook also refers to the nominal value of this number (i.e. without tolerances or class-of-fit allowances) as the "Basic Pitch Diameter". In the UK, it's called the "Effective Diameter" or "Effective Pitch Diameter".
Assuming consistency of units, the calculation of the Pitch Diameter for UNx (ANSI/ASME inch) or ISO68 (metric) threads is the same:
PitchDia = MajorDia - (0.65 * pitch)
For your example:
PitchDia = 1 - (0.65 * 0.125) = 0.9188
continued in reply ...
actually you are a pretty good teacher, don't worry about being boring, you ain't
Thanks. :)
Thanks tom yes got it' I'm on nights this week and find myself a little testing. I cut some threads the other day & they work fine but looked a little rough, I am new to all this but getting on well with both mill & lath. Most thanks to you, question" if you had a thread to cut say 1/4" bar pitch 1.25 would you make your 3/8th HSS tool bit smaller at the cutting end? Say down to an1/8th then put an 60degree angle on it, I'm thinking smaller bar smaller tool bit. Rob
There is no need to narrow the tool unless you are threading to a shoulder and need the clearance. Maybe the next thread you cut will be larger and you'll need a bit wider than 1/8".
Tom
...continued
The calculation of the helix angle then proceeds as you state, but using the circumference of the Pitch Diameter.
Helix = arctan(lead/pi * PitchDia)
= .arctan(0.125/2.8865)
= 2.48 degrees = 2 degrees 28.8 minutes (rounds to 29 minutes)
This resolves the difference between the table and your calculation.
Regards,
ggs
that is osum the tird methed helped me understand the seconed methed
Thanks for watching.
arctangent is just the mathematical name of your measurement with the protractor. I'm sure you knew that already, but for the benefit of other viewers... don't be afraid of math! trig is incredibly useful for mechanical design.
scose
Math is tough for some people, but having an application for it goes a long way toward developing an understanding of it. I was never strong in math in school, but what got me through was seeing it's value in machining. Basic math, algebra, geometry and trig are used extensively in machining. Even if you solve a machining problem intuitively, you are still using math, like it or not. :) . One of the topics on my list of videos is to do a series on basic machine shop math. Not sure how much they will get watched, but if it helps one person see the light, it'll be worth it.
Tom
MUY BUEN VIDEO. COMO PUEDO SACAR LOS ANGULOS DE LA ROSCA ACME
Tom, when I did the arc tangent of .039 I got 2.2334.. which is a different value than 2.278 which you got. I wanted to make sure that I was doing the correct procedure. I wonder what I'm doing wrong? Thank you for your great videos.
You weren't doing anything wrong. That's just a roundoff error. I used .125/pi, you used .039.
8:06 ....I know that you said:
"now just connect the dots", but it sounds like "now disconnect the dots"...
Either you hear the one or the other, funny how our brains work 😊
Interesting how an experienced INSTRUCTOR needs to think (i.e., predict information transmitted like a new STUDENT!
Hi Tom. Just wanted to say thanks for the video series (your whole channel in fact). Helped me greatly in cutting my first internal and external threads on a tool post project.
One question on helix angle. Whats the thinking on grinding these angles rather than just grinding more relief than you need? Ie if you need 2.5 degrees why not just grind 10 degrees to both side reliefs (so the same tool can be used for right and left hand threads with a variety of helix angles).
Hope that makes sense.
Cheers
D
Thanks Duncan, it's good to hear you are enjoying the channel. Don't forget to visit the website for even more information.
Grinding more clearance than necessary is bad practice. The idea is to grind a tool with adequate clearance to get the job done, but one that also has enough material behind the cutting edge to draw away the heat. Without that, the cutting edge will overheat and dull prematurely. This is especially important when threading because so much of the tool is in contact with the work.
Tom
Toms Techniques That makes sense, cheers Tom.
D
Might that weaken the cutting tool? Faster wear?
Makes sense, what about a formed thread tool? How do you add the helix degree to make it cut correctly?
If you are referring to rolled threads, the helix angle is allowed for in the thread form on the rolls.
@@TomsTechniques I'm not sure what it is called but it fits in a quick change holder and is adjustable. You only grind the flat on the top of the formed tool. I have an Armstrong but it's not easy to me to set the angle of rake at center line. I got a lot out of your videos, I watched the threading and the making of a matching nut along with other of your videos. You make it down to earth for a simple hobbyist like me.
Hello Tom, in first place thank you really so much for your useful, really professional tutorials - I have not found much videos such as good as yours !
And in second place one question... You say that the clearance angle for cutting steel is 5º and so you add the 2,5º to that on the leading side (giving 7,5º) and subtract it from the trailing side (giving 2,5º). I do not understand where these 5º really come from ? I mean the material (round steel) would be cut in the same way if it would be 0º ? If the resulting pitch angle should be 2,5º so how it comes the form tool has to be 7,5º ? - Does this mean the cut is 7,5º and the result is 2,5º ?
Also I would find it very useful if you make an explanatory video (maybe only theoretical) to make the differences clear between cutting with a (hand grinded) form tool as you do and on the other hand using an ready made insert tool, where these angles, etc. do not apply !? I am a lathe beginner but I like the theory behind in order to be able to understand and later apply the knowledge to other cases. Thanks for help in advance !
Best regards,
Daniel
+Daniel Reyes
Hi Daniel,
Different types of metals cut best with certain rake and clearance angles. For instance, certain grades of aluminum might machine well with tools that have larger clearance angles, but if you used that same tool on a tool steel, it would quickly dull because it wouldn't have enough mass to carry the heat away. Tool geometry like this is readily available for various alloys online and in machining handbooks such as Machinery's.
The only different between a hand ground tool bit and an insert is that the insert is disposable, and that many inserts are made of carbide. The geometry is exactly the same. I personally do not recommend carbide inserts for beginning machinists because they expensive and very unforgiving. Everything you need in a tool bit can be had in a hand ground high speed steel tool bit.
Tom
Hello Tom, thanks for your answer - I meant that insert tools have no helix angle, that means geometry is indeed different or did I miss anything ? I assume that is because the insert tools are not so high (the cutting edge is much shorter) so that the helix angle on the insert itself would not even have much effect when turning. I am now preparing my HS hand made tool for my first ACME thread, following your great videos ! Thanks so much !
+Daniel Reyes
Carbide inserts have no helix angle because the helix angle is created by the holder. The helix angle with inserts is actually more critical because they tend to use less clearance than HSS threading tools.
Good luck with your Acme thread.
Tom
So when I cut a internal thread feeding from right to left the leading edge would be the right side of the cutting tool and the trailing would be the left side?
The terms right and left are confusing because they depend on your viewpoint. Let's put it this way: The leading edge of the tool is always the side in the direction the tool is feeding and will be the side doing the cutting. In my internal thread video, the leading edge is the one on the headstock side and is the edge doing the cutting. The tail stock side, or trailing edge is just going along for the ride.
Tom
Thanks :) I'm looking at buying a exacto milling machine that was used in a highshool. As a teacher did you ever use one?
No, that a new one on me. We had Bridgeports and Tree mills.
Tom
great stuff! you sound like Norm Macdonald😃
Thanks. You aren't the first to mention that.
You sound almost exactly like the comedian Norm Macdonald.
Great videos, though. Very informative. Where's the last part showing the inside thread?
Can't say I've ever heard him but I'll take your word for it.
There is a three part series called"Cutting an Internal Thread on the Atlas Lathe" that covers the internal part. It's much easier to find on my website, tomstechniques.com than on TH-cam.
Tom
does the outside diameter matter... would u use the same setup for 1.25 diameter?
The outside diameter or major diameter drives the pitch diameter of the thread, which is roughly equal to the major diameter - .6495 X pitch. Other than that, the set up is the same for any size thread.
Hi tom you talk about thread depth, in video 4, pitch over 1 -: 1.5 = ?
So your sum 12 over one ? -: 1.5 = what do you mean by over one!
Rob
Hi Robin.
The pitch of a thread equals one divided by the number of threads per inch. For the 12 pitch thread I was cutting, that equals 1/12 or .0833"
The approximate depth of a thread feeding with the compound rest set at 30º is the pitch divided by 1.5. For my 12 pitch thread, that would be .0833/1.5 = .0556".
Hope this helps.
Tom
Hi Tom, I've been reading up on thread geometry and I'm a bit puzzled. Looking at a drawing, the flat width for an external thread is P/8 at the crest and p/4 at the root. Does that not mean it should be P/4 for the tool flat width? On an internal thread the tool cuts down to P/8 so quite opposite. Can you straighten me out please?
Thanks,
Alan
The flat width on the tool should be P/8. If it were P/4, the minor diameter would end up too large on an external thread and the major diameter would be to small on an internal thread, creating interference.
Tom
Thanks Tom
new to machining so forgive me, but just went thru the 30th hand book and did not find helix index in the threading section.. seems many references are made in youtube videos to the book and I can find a page with any of them.. in thread Constance for example. can ya give me a page number to start looking...thanks
Thank you for all past direction. One thing still is not obvious to me. While turning a external thread,"Why turn the compound to 30 degrees then turn around and line up the tool at 90 degrees to the material. It seems your neutralizing your first move. Can you direct me to some reading etc. I don't see how anything has changed in the moves. Your help greatly appreciated in advance. My threads are taking good shape and pitch diameters in the range as I progress as a true beginner operator.
By setting the 60º tool at 90º to the work and feeding it with the compound set at 30º, the tool only cuts on one side. That puts half the force on it over feeding it straight in, greatly reducing the possibility of chatter.
Thank you, and Thank you again. Obviously the learning curve is steep and even after listening to the video you miss pieces. I looking forward to your video's on internal threading if you have done that.
Well , here is the helix angle I was asking about. When rolling an external thread with a feed through spoke threader why do the three die rollers not cross thread each other when a spoke is having threads rolled on to it?
And, Do they each need to be shimmed a different distance from the rolling head?
Also, it seems like the spindles could be parallel with each other and the dies could be tapered so the thread being rolled would become progressively deeper as it feeds between the dies. This angle would be the same as the taper on a forming tap? The die would be longer than a normal thread cutting button die? I would like to make these myself so I can understand the principles and because they cost so much and because thread rolling is so much stronger than cutting. Yes, You are a wonderful teacher!!
This video provides another piece of the puzzle. Since there are three dies the second die needs to be shimmed away from the head a distance that equals 1/3rd of the lead? The third die needs to be shimmed a distance that is equal to 2/3rds the lead? Also, the dies only need to be tapered for 1 or 2 threads? I am not sure. I am thinking It needs to be a small number or bottoming, thread forming taps would not work well? Those are questions because I don't know for sure if I am right.
I've never used a thread rolling head, but just guessing, the form on the three rolls is likely staggered by 1/3 the pitch of the thread, so each lines up with the form of the roll preceding it. It also seems they would need to be geared together to work properly. I would imagine there is some sort of planetary gearing in the head to keep the rolls in synch. Of course that means you would need different gearing and different rolls for every thread you rolled.
Tom
@@TomsTechniques I just realized the rings on the dies are not screw threads, they are concentric rings like several thread cutting tools right next to each other. Since they have the proper angle and form and they intercept the work 1/3rd the lead distance apart from each other they will never interfere with each other. if we modify the tool to have an outside plate that all three spindles go through opposite the mandel head then the dies cannot spread apart. This way we can make the the whole tool larger for 1/2" diameter threaded bolts.
If we make the tool and harden it then we can create the rings by simply turning a grade 8 bolt between the annealed, tapered die blanks and then harden them also.
You may want to do a search on TH-cam for "thread rolling head" before putting too much thought into this. There is a lot going on in there, including some sort of eccentric mechanism to retract the rolls. BTW, the rolls would need to be ground to achieve the necessary precision.
Tom
The arc tangent is .039 so how do you get 2.3 degrees from that?
Degrees vs radians. Your measuring in radians not degrees.
Why is the width of a flat equal to .125/8? Where did that 8 come from? Would a pitch of .1 use .1/10 to calculate the flat?
alex tworkowski
The width of the flat on any thread is 1/8 the pitch. The 8 is a constant.
Tom
Why divided by 8 because of number of threads per inch?
No. The 8 is a constant that makes the width of the flat proportional to the pitch of the thread. In other words, since you are dividing by 8 for all pitches, the width of the flat on a coarse thread will be proportionally wider than the width on a fine thread.
Tom
The discrepancy between the table value for the helix angle and your calculated value is due to the use of an incorrect parameter.
To calculate the helix (or lead) angle requires the use of the "Pitch Diameter", not the major or minor diameters. The Pitch Diameter is the diametrical distance to a point on the thread tooth where the cross-sectional width of the tooth is exactly half of the pitch.
continued in reply...
1/8=.025/8=.015 so how do you get .016?
He rounded up.
Why not make a tool holder that you can twist the tool to the helix angle? The setup time would be a lot more fast and easy, the cutting force normal to the workpiece too...
Why not? Sounds like a good project to me.
Another option might be to use a round tool bit (drill blank) for the threading tool and hold it in a boring bar holder.
Tom
I see-sorry
You sound like norm McDonald
+Shane K
I'm not that familiar with him, but that has been mentioned before. Maybe he is the one who sounds like me.
Tom
thanks, now that's all I hear
+nik kwasnjuk
Sorry. I didn't start it. :)
UNC stands for UNIFIED COARSE. Not unified "national" coarse. It is called unified because it is NOT national. It is the unification of the standards of USA, Canada and UK.
Easy mistake to make because you are still remembering the American National thread standard, obsolete since the late 40's.
In fact you have calculated the old American National sized flat which is 1/8 P but the Unified Thread flat is 1/4 P and permissible down to 1/8P.