[maxine]

It would be worth a look at the Okuma for sure.

I run all my taps at 500 RPM as well. Lots of guys go much higher in a high production environment and larger machines, but I am happy at 500. No broken taps yet. One thing I do too is add a dwell between the CW and CCW movements. Not much. I use .05 seconds. Works great. My biggest tap yet is 3/8 16.
Smallest is 6-32.

I will look into how to add a brief dwell. Thank you for the suggestion, I appreciate it.