8.25 ID 2 start ACME

[desmotom]

Trying cut a large nut with a 2 start acme and my finish is very chattery. Its 4140 8.25 ID, I used longhand g32 because I have success with it before but not on this part. I started at 250 rpm and now I am down to 75 with same results. Using a single point acme insert (top lock) with a 2 inch bar and going only 2.5 in depth. The test bolt fits good but the finish is errrr.

[mcpgmr]

I have been away from turning for a few years but the first thing that comes to mind besides SFM is dept of cut per pass. Could be it's either too deep or not deep enough and you may have to find the sweet spot to dampen the vibration. Acme thread is blunt and less free cutting. Also maybe use G96 to keep SFM consistant with the diameter being cut. I could be totaly off but I'd mess with the d.o.c. HTH!

[Allan]

Are you changing the start location in z before each pass allowing for an infeed angle of 14.5 deg? If you are not, the tool is cutting on both sides of the insert and you'll most likely never get rid of the chatter. The G76 cycle uses the infeed angle defined in the P address usually 30deg. On a manual lathe we always used 29.5 on the compound and 14deg for an acme thread.

 

Allan

[desmotom]

Yes Allan I am but using long hand method. How are you by the way?