The shank needs to be soft ctxt

The shank needs to be softer than the chuck jaws or it will eventually destroy them. When doing knee mill work it is typical to use center drill to spot holes. And to chuck up taps and power tap holes while you are right on location too. Well this ruins the chuck jaws over time because both of those tools are harder than the chuck jaws. We would often keep a "special" chuck for when we needed it, that chuck did not see everyday use with center drills and spot drills.

Center drills (slight digression here) spot so nice because they are more or less a 1/8" drill bit hung on the end of a 3/8" body. Folks often run them in way up into the 60 degree portion but this is not good practice. If you try that in 4140 pre heat treat, A2, D2, etc when you try to enter into that 60 degree included angle with a 118 degree drill the corners of the drill tip often fail. Just run the center drill in to nearly full dia on the tip, let it sit and dwell with spindle running for one second, and you are done :-). They make 120 degree spotting drills that are short and stiff, and they have a round OD, no relief, they work really nice :-). With the round OD you can put them in a collet with only say 1" sticking out.

Taper shank drills again the shank is soft, they are easily made into a smaller taper size or even a straight shank.

Messages In This Thread