tapping 316 SS 4-40

broke · May 23, 2017

I have a job coming up that requires a bit of 4-40 tapped holes in 316 stainless and was looking for some tips. I do lots of 4-40 and smaller in other materials where I can thread flow, obviously not the case with 316.

I'll be drilling thru about .5 inch and need threads about .35 deep.

Do you get in the cut and keep hauling or should I be breaking the chip? I have rigid peck tapping in the quiver.

I'm drilling .0905 as opposed to .089.

AARONT · May 23, 2017

Use a thread form tap instead of a cut tap and you'll have much better results. Make sure to use the correct drill size for a thread form. Here is a tap drill calculator where you put in the major diameter, thread pitch, and percent of engagement you want and it will tell you what drill you should use. OSG | Taps | End Mills | Drills | Indexable | Composite Tooling | Diamond Coating | Die Products

broke · May 23, 2017

Isn't a thread form tap going to just work harden the stainless immediately and break a tap? Can you get away with it because it's such a small deformation compared to a larger size?

NodecoMachine · May 23, 2017

Thread forming for 304 and 316ss. They like to form more than cut and a thread forming tap is much stronger than a cutting tap

danrudolph · May 23, 2017

I tap 4-40 with cut tap in 316SS on a production job, drilled .089" with a Guhring 9024630022600. Only caveat is that I am on a swiss CNC running oil. I am tapping at 750rpm as well.

I use an OSG 2885000 (MSC 04620498) and change them out at around 300 holes to keep the threads looking nice and burr free, since the parts get inspected for burrs at 20x under a microscope.

I would try peck tapping unless you are really pressed for time.

nihilistic · May 23, 2017

For deeper threads spiral taps are nice for guiding the chip out of the way.

SND · May 23, 2017

With a through hole, spiral point tap all in one go should be pretty easy, or form tap. Good fairly rich coolant or oil, which form tapping would need as well anyhow eh. Worse thing with these smaller Cut taps is always the chips, they're what's gonna break it usually on the way back out if they pack up. But that's fairly rare with a decent spiral point and the chips exiting out the other side.

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tapping 316 SS 4-40

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NodecoMachine

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