OK, here's a question for all you guru's out there.
I'm tapping 5/8-11 holes, in 4140 annealed, with HSS Steam Oxide coated taps, with coolant. (cnc machine) I need to use a H7 rating, because the bars will be heat treated afterwards. To get any other tap would be 3 weeks out, and I can't wait that long. so I'm married to the above tap.
What type of tool life should I be getting?
atm, I'm getting roughly 250 holes and seeing a nice amount of wear on them.
I'm running the tap 300RPM @ 27.2727 IPM , roughly a 50SFM
Any suggestions on getting a better life out of them?