View Full Version : counterbore's
02-15-2005, 11:02 PM
hi yall, im in need of a few counterbores, is there a way of making these out of old hss drill bits, if so whats the procedure please,,,thanks
02-15-2005, 11:09 PM
Yes, a spindex and a surface grinder or via collet in a lathe & a tool post grinder.
02-15-2005, 11:10 PM
I have made one or two with a drill bit. I just ground the bottom flat and sharpened the bottom like an end mill. Setup takes a little time since they don't have a pilot.
02-15-2005, 11:36 PM
cheers, but do the drills have to be softened first? or will carbide tips turn them in their hard state?
02-15-2005, 11:48 PM
Made a few specials by grinding a HSS drill bit, leaving a "pilot stub" (smooth) as a guide. Carbide tooling generally won't machine anything above 46 HRC, so grinding is the easiest way to reshape hardened steel. Never used my surface grinder for these, as it takes only a minute or two on the bench grinder.
02-15-2005, 11:59 PM
I buy Bison counterbores as I need them - they only cost about $5/ea (CDN$) in the smaller sizes - it is not worth my time to bugger an expensive drill bit to make a $5 tool that already exsists. Now, if I ever snap one of my Norseman drills (ain't gonna happen in my lifetime) - I would retip it instead of wasting an expensive alloy drill bit on a $5 HSS counterbore.
If you really want to make your own buy some O-1 and start from scratch - less work, more educational. Make a complete set with interchangable pilots - do a nice job and be proud of your accomplishment.
02-16-2005, 12:53 AM
Here's a way to make them, works for me. Start with a piece of drill rod, or hardenable rod. Either pick the correct diameter, or turn down a larger size for a portion to the size needed. Drill the hole for a pilot rod, then either mill or saw away a 'D' shape out of the end. Grind the appropriate relief angles, then harden the cutting edge. Once it's cleaned up and sharp, loctite a pilot rod into it. You can pretty much make any shape you want on the end. The picture shows it made for a flat bottomed hole. I've drawn it with the 'D' shape too long, it's length should probably be about equal to the diameter of the counterbore. The picture also doesn't show any rake- this can be ground in before hardening, or it can be created by cross drilling a hole near the end before cutting the 'D' shape out. This procedure was shown in an article in HSM a while ago. The fellow was making a chatterless countersink.
[This message has been edited by darryl (edited 02-16-2005).]