[colby2000]

Currently working on a job which is a 4.100 inch long pin with a .090 long head. The head dia. is .240 x .090 and body of pin is .120 x 4.010 long. Material is 303 SS. Probably we're having is holding the TIR of .003.
Any pointers?

[txcncman]

Your material is probably stress relieving during machining. Are you checking TIR at each step of the cutting? Rough and finish?

[holbieone]

is your spindle rpms too high , causing it to whip and bend


I'm guessing the head is to the spindle ?

[MikeMc]

First of all...before we get too far with this, what is the material OD and tolerance? What type of tooling and coolant are you using? I have had this problem with materials like 17-4, but not with 303.

[colby2000]

Material od is .250 with a tolerance of +/- .001. We're using Hangsterfer PC 20 cutting fluid. Cutting insert is Kenametal ccgt3250lf. Spindle running 8000 rpm at .001 upr

[MikeMc]

OK...first of all, I don't know anything about the PC20, but I thought that was a honing oil. We used to use their NG and it was a great oil, but they seemed to be putting gold in it because as soon as the price of gold went up, it did too (A LOT) !

You might want to try an oil developed for Swiss machining, just a thought.

I don't know anything about Kennemetal either, I don't use any of their tooling. We use all ISCAR, they seem to stay more on the cutting edge of the technology.

Speeds and feeds look right to me for our tooling and oil though and the +/- .001 tolerance on the material is fine. Not sure what to tell you at this point.

[colby2000]

Sorry guy's I had originally stated TIR tolerancing was .003. Actually I was wrong it is .002

[MCImes]

We have apart kinda like this. Its a biiitch
I have to turn .750 stock down to .2497-.0004 by 1.9" long with .0015 TIR. I tried different speeds, feeds, roughing and blending...nothing worked. we ended up boring the body and pressing in a ground .2497 shaft then had to indicate them in.

Holding .002 over 4" is really tough in my experience... any way you could get ground stock and press the head on?

Your issue is most likely stress in the material, but other than stress relieving the bars before you machine them I dont know how much more you can do.

[carmstrongls1]

G650 support with sub spindle collet.

I run a job that is very long. Gun drill almost 5" deep and cross drilled etc. Even though I turn the large end out where the ID work is at, and have all that weight out there I held +/-.0007 on the job last two times I ran it. Running 316 and nitronic 60 versions.

THis option of programming is also awesome when threading a section that is longer than the landing in your guide bushing.Just rough turn it. Then sync, Then thread. Zero chatter.

[txcncman]

Run between centers yet?

[colby2000]

GIVE ME YOUR OPINION ON THIS.

[carmstrongls1]

You should be able to turn then sync the subspindle. I promise G650 sync turn is the best way to remain true lengths.