But I've done this 1000 times

The taper tap that broke off in the first hole (F drill) had a half dozen uses in steel without issue. After I drilled the hole .265" per the machinery handbook I used a brand new HSS taper tap to start the thread and the effort was high. I then switched to a spiral 3 flute tap which went thru OK but the effort was noticeably higher than usual. It's junkyard steel and I have no idea as to the alloy.
 
I drilled (.265") and tapped two more holes and the effort was normal. The only difference was that the problem hole was right near an edge. Maybe there was a hard spot in the steel or the part was shear cut near the problem hole? Would that cause hardening? I milled the edge and faced the part when I originally made it so evidence of a shear cut would have been removed. I have also welded this part (not near the holes) and used a carbide tipped boring head on it without incident. Anyhoo, the holes are done and the problem is now academic.
 
epanzella said:
I drilled (.265") and tapped two more holes and the effort was normal. The only difference was that the problem hole was right near an edge. Maybe there was a hard spot in the steel or the part was shear cut near the problem hole? Would that cause hardening? I milled the edge and faced the part when I originally made it so evidence of a shear cut would have been removed. I have also welded this part (not near the holes) and used a carbide tipped boring head on it without incident. Anyhoo, the holes are done and the problem is now academic.
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If you tap while the work is still on the mill maybe this would be of some use to you. CE56054C-B409-4EC3-A61E-388FFC75BF57.jpeg
 
Larry$ said:
Learned something! I just always backed the tap out on thicker material and cleaned off chips. There is a huge difference in the quality of taps!.
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I always back them out every 1/2 turn. Thats the way I was told and at that time the older mechanics (Otis elevator 50 yr's ago) did it, and they also used Crisco cooking lard as the lubricant. In the field if you broke a tap in steel it was a big problem.
 
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Charles scozzari said:
I always back them out every 1/2 turn. Thats the way I was told and at that time the older mechanics (Otis elevator 50 yr's ago) did it, and they also used Crisco cooking lard as the lubricant. In the field if you broke a tap in steel it was a big problem.
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I use gun taps nearly exclusivly to prevent having to back and clear chips. They force the chips down the hole ahead of the tap and you can power tap with them easily as long as your machine and setup are rigid enough.


Any details on that tap handle setup you have?

Ratcheting?
 
Larry$ said:
Learned something! I just always backed the tap out on thicker material and cleaned off chips. There is a huge difference in the quality of taps!.
Click to expand...


We got a new to us brand at work, TDC? and they were horribly hard and brittle.

Granted, we abuse our taps as we need things done NOW (Production stamping) but these must have been designed for perfect conditions in a CNC environment.
 
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