15L Slant Pro Expected TIR on Small Parts

Hello everyone! Long time lurker, first time poster. Experienced in the robotics industry on the design side, but not very experienced on physically doing the machining myself. I desire to learn how to properly machine to build the skill set, and also better understand the parts I design and what the machinists have to do to make them to hopefully make my designs better. Looking forward to sharing knowledge with everybody and learning!

I'm hoping someone can help me with a couple quick Tormach 15L Slant Pro questions. I'm thinking of purchasing one to do some short run production work I have access to, but the tolerances of this work are quite a bit tighter than what I'm used to working with in my normal job. We're talking outer diameter tolerance on headless pins of +/- 0.0002in that have diameter 0.5" and less, and length of 0.5" and less. The other tolerances on the chamfers, grooves, and length are not an issue. And there is no callout for concentricity of the main axis and the outer diameter (though, I obviously want this to be "close"). Some pins will be aluminum, and others stainless steel.

So two questions:
1) Is it possible for this machine (not necessarily me) to at least somewhat reliably perform at this tight outer diameter tolerance of +/- 0.0002"? Scrapping parts is okay as long as it isn't too crazy (e.g. it is okay to make double the needed parts every time to then scrap the half out of tolerance if I *have* to). I plan to do the full automation package (automatic collet closer, bar puller, turret, gang tooling half plate, etc.), so that will be my setup. Probably use kennametal tools (haven't picked out the exact ones yet) and Hardinge Special Accuracy collets, though. Any different recommendations beyond this?

2) How feasible is it for someone inexperienced with machining like me to learn how to machine small pins like these at this tolerance, working at it 8 hours every day for a week or two? I can do CAM programming (but the conversational programming looks really cool) and so understand the steps involved, and I have used many manual machines for years for light duty work with much looser tolerances (+/- 0.010), but never a lathe. Just curious on opinions here :)

Thanks all!
-Nathan

It won't even come c lose to holding those tolerances

+/- 0.0002? yeah that's tight. :eek: At what temperature? The resolution on the machine is probably not that good..... But it might be repeatable once you get it dialed in, it will take some fiddling to get it that close. Resolution, accuracy, and repeatability are 3 different things. To hold those tolerances on my Hardinge CNC I have to warm it up for a couple hours by running it dry and just let it cycle, then it becomes consistently repeatable. Not sure if the same applies to a 15L, but I think this would be true for any machine tool.

TIR should be fine even if the collet is a bit off center. You are working to the spindle rotational centerline, not to the OD of the raw material. The exception to this is if you have to do a second operation on the back side of a part and have to re-chuck it. Then you need everything concentric.

I run a Slant Pro just about every day and I self impose the tightest tolerances I can (even if it does not call for it). Usually I'm in the +/- .001" . - .0005" If I really spend the time to monitor things like thermal expansion of the spindle and tool wear (especially in 304 SS) but this requires a ton of adjusting. As anyone on here will tell you, I'm pro Tormach through and through but +/- .0002" is outside of this machines reasonable tolerance. Some may be able to pull it off but I certainly cannot.

Really appreciate the feedback everyone! Yeah, the crazy tight tolerance was certainly a worry of mine, so I'm glad I asked about it here.

The types of parts I would want to do right now (simple pins and spacers) would not require any secondary operations. Once they are parted off, they're done, thankfully.

So what do you think is the minimum tolerance that is "easy" to achieve on the 15L without getting in the weeds and having to spend a superfluous amount of time dialing it in (e.g. carefully monitoring thermal expansion of the spindle)?

Quote:

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Originally Posted by nwright

Really appreciate the feedback everyone! Yeah, the crazy tight tolerance was certainly a worry of mine, so I'm glad I asked about it here.

The types of parts I would want to do right now (simple pins and spacers) would not require any secondary operations. Once they are parted off, they're done, thankfully.

So what do you think is the minimum tolerance that is "easy" to achieve on the 15L without getting in the weeds and having to spend a superfluous amount of time dialing it in (e.g. carefully monitoring thermal expansion of the spindle)?

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So for me it's like this:

+/- .005" - I can just about put a blind fold on and hit these numbers once I have the tool do a skim cut. Variables include: good tooling - proper too setup/ridged - good work holding

+/- .003" - I just have to monitor things after the setup and tweak the wear offsets if I need to adjust

+/- .001" to .002" - I have to do a proper warm up of the machine (30 minutes) - monitor things closely - keep track of how many parts I can run before changing out the inserts

Sub .001" - forget it. From time to time I need to hit a sub .001" number but it involves walking the part in which takes a ton of time at the machine.

+/- 0.0002 is really more in the centerless grinding range. A Hardinge CHNC lathe might do what you want, at least they start out as a high precision machine. They are basically the same frame as the HLV-H manual lathe. A quick check on ebay turned up 8 of them for $2000 to $17,900. I'm sure there other brands of high precision CNC lathes also, I just am not familiar with them.

But in any case, to hold this kind of tolerance you will still have to babysit the machine.