M8 tap into 304 SS

[Caprirs]

I normally cut aluminum. Sometimes mild steel. Essentially never machine stainless. An upcoming job requires a threaded blind hole of M8 x 1.25 x 12mm deep in 304 stainless. There are 40 parts with one hole each. The quality of the thread is not super critical, i.e., no thread gauge will be checking these.

Should I use a roll/form tap or a spiral flute cut tap? My machine is a lightweight VMC with rigid tapping and a Mitsubishi control. The tap will be held rigidly in a collet or drill chuck. Having no experience with stainless, does a roll tap work well? I exclusively use roll taps on my aluminum jobs.

Thanks.

[kalmah]

Be careful concerning the torque !!! I've already "blocked" a 19Nm spindle with tapping. I don't know if your spindle has enough torque for M8. The cutting force in aluminium are 7xtimes lower than steel or stainless steel

[dpark1]

spiral flute (flat bottom that removes the chips as it taps) works great. I use everyday on my fadal

[CNC_BOB]

A roll tap requires close tolerance hole pre-tap. I know you mentioned that quality is not important so having said that, 12 mm is very deep and if it is a thru hole, I would go with "spiral point" type taps which push the chip instead of pulling the chip up and out of the hole. hope this helps

[mc-motorsports]

You need a spiral point cutter as noted above, get one made for threading SS. A HSS tap made for aluminum and steel won't last long if you make it thru the first hole. And watch your feeds and speed when you drill, don't work harden the material. And have fun, I HATE 304SS! But if your patient and experienced with 304, there is a lot of money to be made.

[zedzero]

Roll tap will have difficulty forming stainless....drill bigger than 6.8...maybe 7.0mm if your tolerance allows it and use rocol tapping fluid and spiral flute tap