CNC Drilling and Tapping 316L Stainless on a Tormach 1100

[@1981Ryguy]

What rpm did you use to drill this hole and what size drill. I have a very similar project in 304 stainless for my pcnc770. I have to drill up to 7/16" for a 1/4 NPT threadmill. Any suggestions would be great. Thanks

[@williamclark77]

That's a letter H drill for a 5/16-18 thread. I ran the drill at 750 rpm with a 2 ipm plunge rate. I normally shoot for 50ish sfm with a hss drill. Peck drilling stainless is hard on a drill but that swarf is dangerous. Don't be afraid to put it in low range so it doesn't stall mid tap.

[@Houcnc]

@@williamclark77 what feed and speed would you use in 5/8-18 tap material 316 ss

[@williamclark77]

@@Houcnc On a Tormach 1100? Low Range and 220ish RPM. Definitely use a sharp spiral point tap if possible. That's pushing the spindle power depending on how big you make the hole. Tap magic or two cycle premix oil will help it not gall and stick.

[@williamclark77]

@@Houcnc I haven't tapped that large in 316. I tapped a good bit of A36 with a 5/8-11 or 5/8-18 (can't remember which) and it did fine in low range. High range and 250 RPM bogged the spindle a lot.

[@gavinbutler4054]

@@williamclark77 is 610 rpm too fast for a 1/4-20 in 304? I’m roll tapping it so my hole size will be .228. Also, are you using a compression head in your video? It didn’t seem like the tap floated at all