Square Peg, Triangular Hole: Holding a Small Tap in a Drill Chuck

[rgsparber]

"...reasonably well centered." The geometry of centering a triangle to a square is not obvious. But I liked the surprise. Thank you for that! Perhaps I find an explanation.

This surprised me too which is why I ran that 6-32 tap all the way in to be sure it was true. A possible answer is in plain sight - the copper wire covered both the square and round part of the shank. The jaw compressed both. The jaws on the round part would center the tap.

Subsequently, I wanted to know if copper over just the round part of the shank was sufficient. I used the wire on a 1/4-20 tap. Then I drilled a #4 hole in the aluminum. With the tap tightly in the jaws, I had no trouble tapping in one inch with no slippage. I used a close fitting rod in one of the chuck's key holes to get the needed torque.

Since I can drive a 1/4-20 tap this way, I expect it will work on smaller taps too.

Rick