[positiverake]

Hello, I'm tapping a 1-8 thread in 304L on a cnc lathe with rigid tapping, it's a 2-1/2 deep blind hole but have room for chips, minor is 3-1/2 deep, I was using a 4 flt hand tap but it broke on the 6th part, I was peck tapping at every 1/2 inch, I put in a spiral point 3 flt and wondering if I should peck or not seeing that the spiral point will push the chips ahead of the tap, I tapped one hole and looked like it was re-cutting the chip, try'ed to blow the chip off, didn't work, I'm using oil. any help would be great. thank's

[Jim Dawson]

I use these in 304. Blind Hole Inch Powertap Cut Taps - GUHRING

But never a tried 1-8 in SS, normally 1/2-20. Don't even know if my lathe would rigid tap a 1-8. These do a nice job of pulling the chips out of the hole. Almost never have any chips left in the hole. If the spec will allow it, try a minor diameter of 0.9219 (59/64) This will give a 50% thread depth, standard for SS.

[positiverake]

Thanks for the reply, I'm leery of of the spiral flute taps kind of weak but I'll take a look, I know Guhring make's good stuff. Have you try'ed roll tap in stainless? strong tap for sure. if I have to I will single point the thread, taps are about $70 and up, gotta find something that's gonna work for the long run. thanks again

[Jim Dawson]

No, never tried form taps in stainless.

I thread mill in my lathe 1''-8, 1.5'' deep for one part I make, in 6061, do it in one pass. Not sure there is a thread mill cutter with a shank 2.5'' long that would do a 1''-8

[positiverake]

This is a Samsung SL45 straight 2 axis lathe, no live tools or Y axis, just big, lots of power, 50 hp.

[Jim Dawson]

That's a lot of lathe Makes my Hardinge Conquest 42, 10 HP seem kinda wimpy.

[positiverake]

Haa, Iv'e run Hardings in the past, all the way back to the AHC and HNC days, Good machines, hold good size, I always hated the left handed control though but I see they do have some on the right now. I still use there 9136 deep hole macro. I'm very surprised how well this big lathe holds size, not bad at all. thanks