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View Full Version : Drill bit shanks as cutting tool bits?



Buckshot
04-25-2004, 06:09 AM
.........Via E-bay I aquired literally 15 lbs of surplus aircraft long shank drill bits. I got all different diameters, fractional, decimal, countersinking, parabolic ........ anyway a bunch!

Since these are so long, like 6"-10" long (and so many) I was naturally wondering what in the heck can I use these things for besides making really long holes in stuff :-). Aligning pins, punches, pivits, crankshaft throws, etc, etc.

Would these be suitable to grind to shape for cutting tool bits? It would seem to follow that they would be (in MY mind) as that's what they were made to do in the first place, right? Lots of them are marked M7 or Cobalt on the shank and I'm thinking it's M7 or cobalt tool steel, yes?

My thinking along this line was as insert type bits in a boring bar application? Internal threading/grooving, etc.

Thanks,
Rick

coles-webb
04-25-2004, 06:40 AM
Yes they are tool steel, probably HSS(high speed steel) some with the addition of cobalt which "imparts red hardness" which means the tool can get hotter without losing its temper. I always keep broken milling cutters to use the shanks as special cutters as they are round and fit better for internal boring. You can also grind them for use a special single flute milling cutters. The only problem you may have is some manufacturers don't harden thier shanks very well or very much as some people have experienced the shank bending while possibly abusing the drill. The cutting end is hard but the shank may not be as drills were meant to have all the pressure along the length and milling cutters were ment to have side load therefore are made completly hard. It all depends on what you are machining. They will probably work on most materials for a time before getting dull. One way to see if the shank is hard is to take afile to it or if you want to be more destructive put one end in a vise and use a hammer to see if it bends. If you are good at sharpening the odd sizes can be used for pilot holes on the lathe or in a mill.

Mike

wierdscience
04-25-2004, 09:54 AM
Drill mfgs leave the shanks soft so the jaws of a drill chuck can grip them easy,things with hard shanks usually slip easy compared to the soft ones.

I find that drill shanks make great pins and punches for special jobs,I wouldn't go in for hardening thou.

Another term for round toolbit is broken or dull endmill,they are usually hard all the way and plentiful http://bbs.homeshopmachinist.net//biggrin.gif

Evan
04-26-2004, 11:30 AM
We have a surplus store in town here and he stocks a complete selection of bastard size drills. All sorts of wierd metric diameters and letter drills for 40 cents each, brand new. I this weekend used my tool post grinder (former cheap drill press) to make a set of step drills for counterboring holes for socket head capscrews. Fun job, and had the immense satisfaction of turning a 40 cent part into a $15 dollar part. I even made one for 2-56 thread.