Tapping 2-56 in 1/8" stainless?

[coors]

Could someone tell me where I'm in error, here? I want to tap a 2-56 hole in a piece of stainless that's around .125" thick. I consulted a tap-drill chart, which told me to use a #50 (.070") drill with a 2-56 tap. I drilled the hole and when trying to tap the hole with a 2-56 tapered, High Carbon, Norseman tap, the teeth are just breaking off. The #50 bit mikes .0685. Am wondering if I'm supposed to use a #49 drill bit (.073) for stainless. Any help that you can offer would be great.

 

[gadget_lover]

It sounds like the stainless may have been work hardened when it was drilled. I'm not sure how to undo that.

You don't mention taping fluid or the use of a tap guide, and both of those might help.

Daniel

 

[StrikerDown]

Breaking teeth and not the tap? Sounds like you need a tap guide to get it started, the tap must be wobbling around to be breaking teeth... I usually just break the whole tap!

Unless you need a really good class of fit try a larger drill/hole.

Stainless can be rather hard, you don't say what SS it is. Did it drill easily?

 

[Anglepoise]

I agree that the hole in the SS is probably a little work hardened due to how it was drilled.

Your problem I am sure is the tap. High carbon steel is just not tough enough for what you are trying to do. Get a new HHS or HSS +cobalt and all will be fine.

 

[mdocod]

To prevent hardening of the steel, use low rpms and high feed pressure (within reason for such a small bit). Using a spring collet to really chuck down on the bit so only as much as you need is exposed will allow you to get it biting and cutting and producing less unnecessary friction and heat.

Using a cutting oil or coolant when drilling will also help keep the heat under control. I would go with the #49 drill (which should give ~50% thread engagement).

I've busted several 6-32 taps trying to go through 1/8" of regular steel, the 2-56 is going to be tricky regardless.

Best of luck.

Eric

 

[coors]

Thank you, for all of your replys! You helped me figure out the problem. The piece that I've been trying to tap is the spring/side-lock side of a stainless folding knife (adding a clip, here). I drilled the hole with the #50 bit very slowly and used SAE-30 generously, stopping often to clean away the swarf from the bit and reoiling. It may just be that since this side of the frame acts as a flat spring that it may be heat treated, I don't know. After reading your suggestions I clamped most of the frame half in a vise and with a very small flame, from a propane torch, I heated the hole and the area surrounding it to cherry red. I then reduced the flame from the area very slowly, because most of this piece was clamped in a huge heat-sink, so that it would get the slow cooling needed for softening the steel. After 5-mins. or so of cooling I oiled a tap and this time it worked flawlessly.:twothumbs Thank you, very much, for the help!

 

[65535]

Most likely a heat treated stainless steel. Now that you said it was a knife part I'm not at all surprised you had issues for future reference whenever possible always anneal the piece when tapping, will safe you a lot of trouble.