Odd tapping problem

A couple weeks ago I had to tap 50 parts with a 2-56 roll form tap.
The material was 303, which is easy to form tap. But taps started
breaking right away. I use good taps, in this case Balax taps were
used with the proper coating for SS. I have tapped thousands of 2-56
holes in all sorts of materials and I hardly ever break a tap. After
breaking 3 taps I knew something was really wrong. So I tapped the
next part by hand and could feel the torque required was way too high.
Upon inspecting the tap under magnification it was obvious that the
coating was failing and the tap was galled. I was using a high sulfur
cutting oil because the high sulfur content is good for high pressure.
Changing the cutting oil solved the problem. I have NEVER had this
kind of problem. I don't know why the first oil I used was causing
such a problem. Maybe because 303 also has sulfur added? I have been
tapping with form taps for over 40 years. I use all sorts of different
taps, both cutting and forming, and have tapped many very difficult to
tap materials. The smallest taps I have used were 00-96. I didn't
break any of them. Anyway, I just though I would pass this along.
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What was the 00-96 for?
Reply to
Tom Gardner
A the risk of sounding overly cautious... did you check the hole size? Such small taps I would think are extremely subject to problems from hole variance. I know you know what you are doing, but sometimes people overlook the most obvious things... and some tapping fluids allow taps to do miraculous things.
Reply to
Bob La Londe
The 00-96 holes were in the heads for ultra sound machines. The part that gets pressed against the body. There was a rotating head inside a plastic case and the screws retained something or other. Yeah, I checked the hole size. Then I looked in Machinery's Handbook just to double check. I'm gonna talk to Balax and ask them if they know what caused the galling and loss of the coating. Eric
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Chinese/Korean steel has been in the news lately. Anyway from the web: "Cold Working Minor deformation is possible with this alloy, although it is not its strong point. Type 303 Se is superior in this aspect."
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