In Reply to: Tapping posted by Duane S. on 08/14/00 at 7:26 AM:
There are several variables incolved in tapping on an old CNC machine. I assume the machine in question does not have Regid Tapping because of your reference to tension-compression.
Tapmatic heads generally work very well although they need yearly rebuilding. Tension compression is the most common way. Holder's vary, I had the best success with Kennemetal straight shank holders that go in a collet chuck. You also want to make sure you are using the right tap style for the material.
Programming tips, set your tapping R point at least .300" above the work and do not program any dwell. Be sure the hole is as deep as possible. Roll form taps are very helpful also in gummy materials like copper. If tap depth is critical you'll need to intentionally set your tool offset high, check the 1st hole & adjust. Do not try to go back in the hole unless you have rigid tapping.
Drilling is crucial. If you're not using the new style drills, like the square drills with no web, your hole must be spotted. Any drill walk is deadly to any kind of tapping. Spotting drills are fine, you don't need a centerdrill unless the surface is uneven.
I have many years of experience and would be glad to discuss the specifics of your problem. Send e-mail to firstname.lastname@example.org. I'm the Tech. Director for the NTMA and it's my job to help out.