Bobw
Diamond
- Joined
- Feb 8, 2005
- Location
- Hatch, NM Chile capital of the WORLD
I was running some 3/8-24 form taps in 1018 a while back 1/5" deep. On the retract, about half the time I was getting threads ripped out of the top, like 6 threads, so I just went in a bit and had someone finish them off with a hand drill. Fadal, so I blamed the machine.
So now today, on a Mazak, blind hole, same 3/8-24, 9mm drill, .69 full thread depth. First couple came out beautiful. BTW I pecked since all my tear outs had previously been on the retract, I figured the coolant was just getting sparse. Well today, on the 4th hole, the tap snapped on the retract. Slowed the surface speed down from 85 to 60sfm, and on the second hole, I lost the bottom two threads on the tap. The taps were OSGs. I've run 3/8-16 on this machine .5" deep at 1200 rpms and never had a problem.
I know 9mm leaves 75% thread, and the next highest drill will most likely leave my minor diameter too big. Am I doing something fundamentally wrong or are finer pitches just a bigger pain with form taps? A floating head possibly, tapmatics rigid tap toolholder maybe? A different tap, more or less SFM, ream progressivly bigger until I reach my maximum minor diamter.
I'm at a loss, and I am not tapping all of these holes by hand, and I don't think a cut tap is going to be a good choice in a blind hole that deep,
Any suggestions?
So now today, on a Mazak, blind hole, same 3/8-24, 9mm drill, .69 full thread depth. First couple came out beautiful. BTW I pecked since all my tear outs had previously been on the retract, I figured the coolant was just getting sparse. Well today, on the 4th hole, the tap snapped on the retract. Slowed the surface speed down from 85 to 60sfm, and on the second hole, I lost the bottom two threads on the tap. The taps were OSGs. I've run 3/8-16 on this machine .5" deep at 1200 rpms and never had a problem.
I know 9mm leaves 75% thread, and the next highest drill will most likely leave my minor diameter too big. Am I doing something fundamentally wrong or are finer pitches just a bigger pain with form taps? A floating head possibly, tapmatics rigid tap toolholder maybe? A different tap, more or less SFM, ream progressivly bigger until I reach my maximum minor diamter.
I'm at a loss, and I am not tapping all of these holes by hand, and I don't think a cut tap is going to be a good choice in a blind hole that deep,
Any suggestions?