Why Would You Ever Use CONVENTIONAL Milling??? | Climb vs Conventional
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- เผยแพร่เมื่อ 6 พ.ย. 2021
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#CNC #Machining #Machinist - วิทยาศาสตร์และเทคโนโลยี
When cutting plastics, you'll get less fuzz on the part with conventional. Also, you can get straighter side walls (less taper) with conventional. I don't use it often but it can be useful at times.
this
HDPE and UHMW love a conventional cut.
You dont want to climb mill with a vacuum chuck either lol
I own a plastics fabrication shop, and also use strictly conventional cutting on my CNC.
Can confirm.
2:23 isn't strictly true, even in climb milling, the flutes of the cutter still cause cause upwards cutting forces on the part. Just because you are feeding in a different direction does not mean the cutter is going in the opposite direction. The cutter is still turning in a right-handed fashion, thus the flutes on a conventional end mill still will exert an upwards force.
The thing about pushing work pieces downwards is only true when the cutter has a LEFT HAND SPIRAL, but still cuts right handed. That is, it still rotates and cuts in the conventional right handed direction, but the flutes of the end mill have a left hand helix to them. This is the only scenario resulting in downwards cutting forces on the work.
i was right about to comment just the same, thank u
They're called compression bits/mills and are fantastic for some applications in plastics and wood. Because of their downward cutting force, they can leave a cut with almost no burr at all.
@@Pow3llMorgan actually compression bits have left hand spiral flutes on one end of the cutting edge & RH on the other end... & are for giving cleaner edges ... I have only ever heard of compression cutters for routing wood to prevent tearout , never heard of metal-cutting & the fact that the swarf is "compressed" into the centre seems like a bad situation for milling metals... 🤔
What about heat input? Does the input become higher with left hand spiral?
There's upcut routers (right hand helix), downcut routers (left hand helix) and compression routers (LHH for top half of flute length and RHH for bottom half). Knowing the difference is especially helpful in routing or side milling laminated materials where your flute helix direction can separate the layers (in something like plywood or carbon fiber).
Helix angle is axial rake and rake is related to cutting efficiency. A positive axial rake is right hand helical in a right hand cutting tool and is more efficient at cutting. A left hand helical tool is negative rake and is a less effective cutting action....just like an old school hand ground HSS lathe tool for steel would be ground or held negative. It protects the cutting edge, but is less effective.
The LHH is used for a different reason in these downcut and compression routers.
Was in a shop with a very experienced fellow machinist on a CNC mill and a was getting poor tool life from cutting some laser cut parts. I told him to conventional mill them and he was horrified at the thought but ended up getting 4 times the tool life. Sometimes it’s just better to get under the hard skin rather than crunching onto it.
That's one of the exceptions to the rule, and a common mistake not realizing that digging underneath the hardened surface avoids wear more than smacking into it from the beginning. Same thing with plasma cut parts as well.
@@platinumsky845
I remembered another one where I climbed and regretted it. Some long finned alum heat sinks were saw cut and needed trimming to length, the first fin that the end mill touched just went ba-doing and bent over. Duh, I just should have seen that would happen. Idiot. Conventional after that worked fine.
My thought through the entire video. Always best to rough out scaled up stock with conventional milling, unless you're not concerned about teeth chipping.
@@michaelslee4336 damn, I can imagine that sound 😬 not relates to climb/conventional milling but had something similar happen when a company I worked for was trying to kill copper components for an EV, it has a heat sink built in and we ran a few of those parts just fine, the customer asked for the heat sink to change a bit to better match air flow and when we milled the new parts the cutter grabbed the new fins, pulled the part from the vice, and threw it against the wall of the enclosure hard enough to make a small dent 🤯
tell him he needs to get the backlash solved in his mill. (that's why his tool life is better with conventional milling)
Conventional cutting works better in foam in my experience. Climb milling tends to push the foam into the part since the foam is pretty compliant, leaving a subpar finish. Conventional leaves a nicer finish in the foams I've cut, since it's peeling the foam away rather than compressing it in.
Excellent video. I'm an old toolmaker and we used conventional almost always on our manual mills because we didn't have zero lash lead screws so the part would try to jump forward during climb milling. Nice to see the technical advances that allow the option to climb mill.
Conventional milling machines do not incorporate ball screws and preloaded ball nuts, so conventional milling is still necessary on such machines.
I work in aerospace and we are using 30,00rpm spindles with 150hp milling large structural components. We have went back to using conventional when finishing. Using a 1/2" dia 4 flute we are taking 1" doc or up to a 10:1 wall thickness to height ratio. Using conventional cutting we are able to feed at over 400ipm and not have these thin flanges push off enough to be a problem.
That sounds like a bad ass piece of equipment bro!
What machine has 150hp and a 30,000rpm spindle?
@@gooblio There are quite a few actually. As far as I know they are all designed for aluminum aerospace parts. The two that I am most familiar with is from Bavius and Starrag. These high horsepower / high speed spindle machines normally have spindles manufactured from either Kessler or Fischer which have actually created a 240hp spindle, but I've never programmed one of those.
th-cam.com/video/fKMruYCQqXU/w-d-xo.html
I would love to see that spindle rip the Alum off the part.
Conventional cutting was used on a manual Millers climb milling on these old miller's will pull your part in or through
Bingo.
good to see someone who has some understanding of the two.
mill scale on mild steel is always conventional until part is clean.
Working on a Bridgeport mill, I was taught to rough conventional, finish with the climb. But you have to understand depth of cut and speed affects it a lot. I rough cut about .050 at a time and finish cut .005. This is with a .750 end mill at 700 rpm. On my finish cut, I go back and forth a few times which might be called a spring pass.
If I tried to climb mill .050 on a Bridgeport I think the cutter would keep pulling on the backlash of the table. Maybe it would work fine with a new Bridgeport, but with these older machines, you need to use different techniques to get them to hold thousandths. With a rigid new cnc mill, you simply take cuts differently than on an old manual mill.
So you side step .050 fir roughing? Is that your max side step when usung the full length of the endmill? Hopefully i worded this question correctly.
Your Exactly right manual machine bridgeport mill & lathes ,machinist for 35 years
When i first started on the BP, cutting Alum on a climb with a roughing mill. I learned fast how back-lash works. Damn! That was a sharp mill.
@@rossilake218 nothing like have 0.050 back lash in a Bridgeport lol
Conventional milling is useful for loading out backlash in knackered machines and for balancing forces in parts that move/flex whilst machining.
Came to write the same thing, on older worn machines you take a big risk of a broken cutting tool and ruined workpiece with climb milling.
Climb is definitely a more efficient way to remove stock, however if you can do conventional milling on a return stroke it could be faster overall than a non cutting return pass with positioning move as shown at the start of this video.
Great video! I have two other thoughts that might help someone else out too.
1 - the conventional approach to case hardened material also works amazing for flame cut profiles. Use a heavy stepover and get under the slag in virgin material and pop off the slag. Then climb cut once the slag is gone. Great for weldments.
2 - I once made some parts with a 10” diameter bore by 4 inches deep that needed less than .001 taper walls and a critical diameter. Taper was a serious concern and the material was a hardened 15-5 stainless. I ended up using a 1 in dia Fraisa 11 flute finisher and climb cut to size using air only (CAT40 spindle). The walls were tapered by .0015 or so. Then I ran a conventional cut spring pass. What that will do is suck the button of the endmill into the cut a straighten the wall. Then did a final ghost pass climb to fix any smear and ended up with walls with .0002 taper. Amazing. Real life saver to learn that trick from Fraisa apps.
It depends on application and machine used. Good machinist know the difference and know how to use that to their advantage
thats the only true thing here!
Conventional milling is also used when milling brittle materials. Brittle materials typically can't withstand the high cutting forces exterted as the cutter leaves the material, causing fracturing and chipping of the base material. I learnt this milling PVC.
I’ll never forget the demo for why you don’t conventional and climb cut on a manual machine when I went to TC. An old WWII era horizontal mill with an 1 1/4” hog climb cutting 1” deep and that thing exploded!
I had a large cutter explode while climb cutting. It was like a hand grenade going off and threw razor sharp metal shards all over the place. I felt one shard touch my hair as it passed by (and my hair was short). I looked behind me and saw the shard embedded in an industrial steel window frame. The grim reaper missed me by a fraction of an inch.
@@gaiustacitus4242 Yep… you learn to duck… or else… shops are much safer, now days. It took a lot more HP to cut with those, at low rpm… lotsa potential energy, when something breaks…
I started my apprenticeship in 1973. Small company with more backlash than you would believe. One M/C had over 3/8” (10 mm) of backlash. If you climb milled you always snapped the cutter unless you were very quick to disengage the feed. Visiting a small company last year not much had changed. If not a CNC m/c ask somebody as not everybody has the best tech to do a job.
I'm a bit younger than you but had a similar experience. Went to an engineering college with some pretty abused and worn machines. Climb milling was strongly discouraged because of the risk of breaking tools, ruining workpieces and worst of all having workpieces flung out of the big horizontal mills.
I worked in a racecar shop that had on old taiwanese lathe. Damn thing had an inch and a half of backlash
I was at school for a manual mill class and started working on my first project. Not knowing the difference between the two, I climb milled a part and noticed the tool move, along with the digital readout. I had absolutely no clue what was happening until I did some research and figured out that the machine wasn’t rigid enough for it. I genuinely thought I broke the machine because of a .050 pass
A milling tool shattered every now and then in my metalworking classroom, and I destroyed one too
Always wanted to know this, I've been taught about conventional and climb milling but conventionally milling has always been avoided. Nice to understand the applications of it!
The times I use conventional over climb is when cutting something that has a hard scale on it. When conventional milling, the cutter cuts underneath the scale first. Climb milling makes contact with the scale first every rotation resulting in chipped inserts.
So useful. Maybe one of the most useful videos you guys have put out in a while. I mean I love the CNC apron watching a tool the size of my forearm blowing into hard steel as much as the next guy, but I way prefer these educational videos that bust myths
Sometimes cutting conventionally with larger diameter tools with straight flutes or teeth like woodruff mills helps guide and stabilize the cutter.
I'm hobby guy on a BP in the Garage. I like to climb on alum, plastics are a different story. The good thing is i can "TEST" cut and look at surface condition. 👍
Interesting point about machining surface hardened materials (better done in conventional) - hadn't twigged that. There's always something to learn - many thanks!!
Spectacular video. I'm just a home gamer, and I've never understood why conventional milling produces such poor surface finish on some materials. This is the best description I've ever heard. Thank you.
Get out there an buy a $1500 Bridgeport, put it in the corner of moms garage and learn. Lots of great YT vids. Get out of the basement!
Everything said here is correct.But 5 extras points.
1)Climb milling extends cutter life 2 fold ,even more denpending on circumstances.
2)Ive climbed 57/58 Rc without issues so i would still recommend climb.
3)coventional does induce less pressure on work pieces so as you said thin extrusions,unsupported nylons and plastics can benefit from this stance.
4) I would still conventional mill with slitting saws.
5) Like you said it comes from manual machinists struggling with grabbing but one can overcome it .
Thanks for the channel and this insights shared.
I'm not even nearly a machinist, but as a scientist this video warms my heart. It doesn't just propagate dogma, but it gives a reasoned account of why climb milling is superior. Of course the comments show that not everyone agrees, but because the video is so clear, the comments too are reasoned responses.
I embraced climb milling from the beginning just because... I had the feeling/sensation that the tool was working better. I always had some shivers by thinking at the tooth rubbing the surface in a convention milling... brrrr!
Now I know from comments here that conventional milling can be useful in case of thin walls and soft material like foam. That's a good advice.
Awesome vid!!! And all in a few minutes!
Easily the best practical description I've heard yet, comparing and contrasting conventional & climb.
You would like to do conventional on plastics as well, because the plastic moves a lot, and with conventional you pull the plastic into you cutter, instead of pushing it away
Nope. Conventional cutting adds too much heat to the equation. Plastic's relative soft nature also make conventional cutting a bad idea is because it increases tool/cutter pressure actually pushing the part away from the cutter.
basically what i remember except for the case hardening, that's a really good tip and i can see it saving several endmills, even in a single job.
As someone who's ever only seen CNC machines do work, but never actually learned about the process, this was very informative. Great work explaining everything in a super digestible way 👍
Found out the hard way plenty of times that tall thin features on parts need to be done with a conventional cut. Most of the time I'd do them in a high number of steps and towards the last couple of steps the cutter would just grab and pull the part into the cutter. Using a conventional cut it almost seems to push the part away slightly due to that shallow entry cut.
Best video ever, hands down, thank you my friends. Most information per syllable since E=MC^2
I have a 50s Sheldon horizontal mill and have always read not to climb mill,, but my mill motor rotation is conventional and I agree with you just makes sense it's trying to lift peace and pile up chips in it's path
One of our mills at work is a 1970's bridgport knee mill that has been abused for decades. When milling you have to use conventional milling otherwise the cutter will bite into the part and bounce the table resulting in uncontrolled sizes and surface finishes.
Managment will not pay to fix it and they won't replace it because it still works.
Conventional milling can be useful if you material is flexing, for example, thin wall parts, however in order to effectively conventional mill your tool must be very very sharp, and its ideal to have a higher ipt, to make initializing the cut easier.
Great explanation! It is good to understand the benefits of both, sometimes the smallest changes make all the difference.
You never cease to amaze me with your depth of knowledge.
I’m a visual person, and although I know the difference and benefits of the two types of milling, some people may have a hard time without visual representation. But this is a great topic, and I appreciate you guys! I love what titans stands for!
Best video you guys have put out in a long, long, long time.
extra long cutters is a good thing to use conventional cutting climb milling pulls the cutter into the part
Great audio. The video seems to show maximum removal rate be going with both climb and conventional cutting (most of the time). An explanation of the versus climb only or conventional only to tool wear, cutting time, etc would be very useful.
One of the better videos from your team. More about machining education then other subjects.
I don't run a CNC machine, but this was fascinating. Thanks.
“ I like your funny words magic man”
This quote from JFK perfectly summarizes what I’m thinking while watching this video, not understanding anything about milling. But I like it
You should use climb milling for walls, thats a must. And use conventional for pocketing/ floor machining. This is for best finishes.
Very nice video. A shop owner where i work, used to program cnc before he hired me. He is an old school guy (retired now) and he used to do conventional milling in 316 ss all the time. He was really suprised when i started cutting with climb cut, telling me its a wrong way to approach 316SS. But, when i showed him a surface finish he said its good for finish cut only. Combining both, climb and conventional, for roughing seemed to be the best. 3:03 This video made me thinking maybe the old guy was right. 316SS is a perfect example of case hardening
316 stainless is extremely prone to work hardening, therefore climb milling would be generally preferred. When milling, there is a minute amount of displacement that happens before the cutter actually bites into the material. This compression of the material is working it into a hardened state, conventional milling exaggerates this effect substantially over climb milling. Once you break the outer crust of the raw material it is substantially softer, if you have ever worked with rolled plate you would know exactly what I mean. Climb mill all of the work hardenable grades unless there is a specific feature that requires the stability of conventional milling.
I should also add that tooling choice has a big impact on the method chosen, if your using flexible flimsy HSS tools then they might benefit from the stability of conventional milling. HSS also generally has sharper cutting edges than carbide allowing it to dig in and not hammer on the material as much. This could also apply to extended reaches and long tools in deep pockets where there may be some flex due to length.
Stabilizing the cutter with conventional milling can be very helpful especially with less than 1/2” diameter tools and/or greater than 2xd doc, even in average cutting metals
WOW..the most straight forward discussion I have ever heard about cutting modes. Thank you.
Ironically, the example machining in the video demonstrates machining techniques which are contrary to the recommendations.
I use it on plastic. It makes a better finish on certain parts.
I do the same thing, especially with Delrin. Always comes out smooth and shiny. 😎
Yes. And I also use conventional when cutting black foam for bottom of shadow boxes.
Climbing will not do a clean job.
Honestly never thought about that. Going to have to try it the next time I cut some
@@josephcampise9950 I work for a plastic molding/extrusion company. So I'm dealing with pre formed parts. What works well also are single fluted end mills with a downward spiral..
Super clear and direct information- great video.
I use conventional cutting all day long in our plastic shop. Along with standard carbide end mills we use router bits in some cases and most plastics need extremely sharp tooling and need to throw the chip immediately, unless you want a goo ball. Acrylic and Acetals you can climb cut without a problem along with some other stiffer plastics. Conventional milling when machining plastic is the norm.
Yup conventional is great if you are cutting hard scale or harder material it gets under the "bark"
Great explanation of the two! Cheers.
I climb to finish, even on manual machines, provided that the table clamp will put reasonable pressure. I may have to rough out, by conventional means, but I'm climbing on finish pass, for sure.
I'm from Quebec in Canada studying as a mechanical engineering tech in college. This course includes conventional and CNC machining, and we never use conventional milling always climb milling only. We were told conventional cutting can have some advantages on a conventional because of screw backlash but that's it's pretty much pointless in CNC because they usually always have anti backlash systems and much higher rigidity.
Really interesting. At first I thought it was John Goodman. But, I learnt a lot from you just then. Thanks. 😊
Excellent advice here! Going to rewatch this one and take notes.
Nice video! I use climb milling on everything from steel to acrylic. Always get a nice finish and my end mills last a long time! It's all about speeds and feeds. If you get those right, you'll always end up with a nice finish. conventional on plastic generates a lot of heat. Climb milling plastics evacuates the chips and heat like you said.
Great video and explanation! Thanks
I've only done conventional milling on some 4140 when a tool broke and the material got work hardened just to remove the work hardened material.
Once in over 30 years of CNC milling that I remember.
I use both when I'm roughing in a hurry.
Great simple explanation, thankyou 👏
I actually just learned something.. I always climb mill anyway.. Just how I was taught. But never explained why. Thanks.
You shouldn't be trusted to make programs for machines if you can't understand what the applications for climb vs conventional are and the benefits of either.
I work in wood milling on flat stock sheet mills and 5 axis milling and the direction of cut is very important for finishes. I dont know much about metal so It does sound as if all you would likely want is climb cutting. I use about 80 percent climb cutting and 20 percent conventional. Mostly for finish reasons.
Climb cutting on a manual mill with acme thread screws would (1) pull the workpiece (and your hands) during the cut, and (2) when the cut would first enter, it would take up the slack in the screw and your chipload would instantaneously go much higher than you planned for, often leading to a broken cutter. None of this happens in conventional cutting.
Also, tool deflection during climb cutting is away from the workpiece, thereby tending toward making your parts oversize (i.e, you don't blow the dimension). Tool deflection during conventional cutting sucks toward the workpiece, thereby tending toward undersizing your part.
Thank for this information 🙂
My machine has worn ballscrews which aren't worth replacing for the situation I'm in. Climb milling circles are out of round by upwards of 10 thou, conventional milling circles are only out by about 1-2 thou. It's because the cutting loads are always going against the backlash rather than trying to get ahead of it.
I remember reading that conventional helps with long tools and tight corners. We had a lot of programmers that would let 1in cutters climb cut into hard corners of h13 and blow the corners off the inserts.
I'm sharing this channel with my apprentice 👍
It's all the undesirables thats correct Barry, I did my learning on shaping mach bk in 84 & tooling was All, on Mill ya tool works hard just index it & carry ON, Titan long live TOOL MAKERS
I was always told conventional milling was always bad on a CNC machine, unless you are finishing softer materials like brass or aluminum. Some say conventional makes better surface finishes on last passes on these softer metals, I have yet to try it for myself.
Plastics like UHMW and HDPE I climb cut. Its all about the materials, sometimes it's better to climb cut to reduce chip weld.
Thanks man its what I was surching for
Brilliant advice.
Well explained.
I am cutting a shallow slot (in stainless steel), then slightly enlarging it to desired width on the return path. I use conventional milling, because climb milling pushes the material against the edge making a bigger burr. The original slot has both a conventional side on the left and a climb side on the right, so the return path cuts on the original right side to remove (minimize) the larger of the original burrs. (Doing it with climb milling on both sides is not really much different...)
Spot on truth! thanks for sharing!
Also, when your Z axis or tool is not so rigid, you can see the difference in flexing. The one tends to pull the mill in the work, sideways, and the other pushes it out.
A big one if you use climb with conventional milling if you almost can drop the roughing cycle time in half for simple soft parts.
Very true, as you can see in this video! Bi-directional roughing can save a ton of time in certain applications.
"I hope this clears up any confusion..."
*me, who knows nothing about any of this*: Nope! Still incredibly satisfying to watch though!
Apparently I watched this a year ago. Came down here to make the exact same comment lol... help
In CFRps conventional is used in order to prevent the push of material inside the part and, thus, causing damage and delamination.
Also for very very hard matterials (58hrc or more) or surface hardened steel (f.e. after laser cut) it's sometimes better to cut conventional to prevent tool crack, but it depends on tool type (hss or carbite) and quality. I work in Poland where many companies uses cheap tools or used, sharpened tools and then the conventional milling for hard steels have a point :D It all depends on situation.
When you cut some soft materials, like delrin, and when you use an opposite flute cutter.
I only climb mill on a manual vertical mill if my endmill is at least half the cutter diameter to keep it from getting sucked into the backlash. Even then it can be nerve wracking at the end of the pass. I try to climb mill when possible, and almost always on finish passes.
When I was working in the 90's at a local factory, our tool shop cnc programmer, who wasn't a machinist, was having a hard time figuring out why a 1" roughing EM kept pulling into a cut during a full diameter conventional pass in the VMC's. We were machining tool steel spacer plates. Because of this, the finish pass wouldn't clean up, and the finish profile was distorted, full of burrs, and a mess. I tried to explain climb milling to him, but he wasn't getting it. Then I said to him to the effect, "You have ballscrews, use them." To me it was common sense. He thought I was crazy. I tried to explain it to him further, but he just laughed about it, and kept using conventional milling. After I left there, I wondered sometimes if he ever figured it out.
Running heatsinks with thin walls and intersecting cuts works great with conventional milling. With climb milling it becomes an exercise in misery.
I'm gonna say, for a lot of people (not companies) the reason is because CNC costs about 100x more than milling. There are a lot of things cnc can do more easily, but you pay a premium for that. You can learn to do the same on an old beat $500 bridgeport, and then you have more knowledge and skills and have saved a lot of money.
Now if customer is paying $5,000 for a part and you already have every machine under the sun, and it's up to you to pick which one to use, this video is for you!
He is talking about conventional vs climb cut
Great video!
For the finish cut with end mill which method should be applied for good surface finish.?
the reason for using conventional is because most manual mills have normal drives and not the high precision no play things so there is a good bit of play and thet is compensated for when using conventional but with cnc mills that almost always have those special drives for the axis
Great video as always, but was wondering if you could expand on the point you made about the variation of lift in conventional vs downforce in climb? I thought that was mainly dependent on the flute geometry? eg using a compression cutter to keep tearout to a minimum on composites, or the high speed toolpaths matching flute helix angle to the feed rate in order to resolve the cutting force inline with tool axis? sorry if this is a stupid question, keep up the great over there!
It's two years later and I don't see an answer to this question. I believe there's functionally no difference in "pull up force" between climb and conventional milling, the only time where it could matter is in the uncontrolled regimes of thin part "suck in" or backlash release (so instantaneous high loads) and perhaps when dealing with hard cases, that might also produce a high initial load as the cutter struggles to cut through the case. Otherwise I agree with you, it's cutter helix and engagement volume that would determine pull up forces.
When you were talking about hard surfaces and conventional milling the skin off would this be advantageous with flame cut billets too????
Not sure why this showed up in my algorithm but cool!
Lots of applications for conventional cutting, mostly when finishing. For ex, if you need to remove .0015 or less particularly in ferrous steel it helps the tool suck to the workpiece. Climb cutting will sometimes just glance off and not cut esepecially with long tools. Also some materials get better finishes cutting that way. Back in the day, lol, climb cutting was risky. Today climb cutting is 95% of the time.
Both have their place to a good machinist
Conventional cutting when machining wood is used to eliminate chipping as you always need material to back up the cut; especially when machining around sharp corners, but I agree that you should always climb cut whenever possible.
If you're machining cast iron/steel parts conventional milling can save you a lot of tool life.
All that slag junk on top of the casting can ruin a cutter pretty quickly.
Conventional milling typically breaks of the rest of the surface contaminations when exiting the cut, keeping your end mills nice and sharp
The guy who made the captions for the CNC footage! The unspoken message is you cut in both directions to get stuff done faster?
actualy one of the more important things learn in milling
Backlash compensation in the control isn't going to do anything for the problems with climb cutting on machines that have a lot of backlash. On those machines, when the cutter engages, the slack is closest to the screw. Climb cutting results in the cutter pulling into the work, immediately jumping by the amount of slack. That can break a cutter if there's more than a few thous of slop.
Modern CNC machines with ball screws don't have that sort of slop in the mechanics.
I usually go with whatever makes a nicer finish. I like going in a spiral as it's easier on the tool cutter. However if it's a long part, I seen a 1in ball just blows in a zigzag direction. Which is good for speed but it usually leave an okay finish. ( Not my choice but the programmer choice) However, I have to flip the part over and it usually becomes a problem if the tabs aren't sanded down and I have to waste time using an orbital sander to smooth out any imperfections so it would vaccume seal right plus clamps. Which tells me the programmer lacks experience. So I quit. I found out the company still sent it out to get remachine to final size because set-up wasn't done correctly. The other place didn't even use a vacuum fixture and just clamp it down.