I recently bought a bunch of MT drill bits at a garage sale. On closer examination, it looks like the corner of the lips are blown out. I tried sharpening one, and the corners just get blown out again. Looking at the sparks, these are not HSS. That's the problem! Do these require major surgery?
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Rescuing a vintage MT drill bit
- Thread starter ericc
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- Feb 2, 2013
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may just have to run them very slow
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They would be carbon steel drills. Suitable for wood, very problematic for metal.
"Carbon Steels : Their use is restricted to the cutting of soft metals and wood. Performance is poor above 250 ℃ (482 ℉). Carbon steel is used primarily to make the less expensive drills, taps, and reamers. Carbon steel is seldom used to make single-point cutting tools. Hardening in carbon steels is very shallow, although some have a small amount of vanadium and chromium added to improve their hardening quality. The cutting speed to use for plain carbon tool steel should be approximately one-half of the recommended speed for high-speed steel. "
www.cobanengineering.com
"Carbon Steels : Their use is restricted to the cutting of soft metals and wood. Performance is poor above 250 ℃ (482 ℉). Carbon steel is used primarily to make the less expensive drills, taps, and reamers. Carbon steel is seldom used to make single-point cutting tools. Hardening in carbon steels is very shallow, although some have a small amount of vanadium and chromium added to improve their hardening quality. The cutting speed to use for plain carbon tool steel should be approximately one-half of the recommended speed for high-speed steel. "
Cutting Tool Materilas, Carbon Steel, Hish Speed Steel, Carbides, Titanum carbides, Straight Tungsten carbides, Crater-Resistant Carbides, Coated Carbides, Laminated Carbide
Cutting Tool Materilas, Carbon Steel, Hish Speed Steel, Carbides, Titanum carbides, Straight Tungsten carbides, Crater-Resistant Carbides, Coated Carbides, Laminated Carbide
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- Jun 7, 2013
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Have a garage sale! Carbon steel drills are usable, if run at the proper speed, as stated above, about 1/2 the speed of a HSS drill. One must use a lot of care in sharpening them so as to not overheat them, if they show any temper colors to speak of, the hardness is reduced and the edge will fail.
Hi. Thanks for the tips. I think that I am having trouble sharpening them. I tried to run the 53/64" bit at 225 RPM. That may be a bit fast. It blew the corners of the lips out as soon as it touched the mild steel. Most of the bits in the lot were HSS. I like "blacksmith" boring bars, since they don't require much grinding and don't use much steel. When you have ground them away, you just forge another hook shape on the end, heat and quench, and you are good to go. It's difficult to do that with HSS. You have to treat those boring bars very gently, but they can cut a lot of steel. I've used small carbon steel drill bits to make lathe tools, and they work reasonably well. Those big drill bits are troublesome, though. Perhaps they have gotten cooked once upon a time, and I need to grind a lot off them, slowly, before they will work. I made a small boring bar out of an allen wrench and hardened it with wrapped steel wire and brazing paste. It worked great, just for the one time I needed it. The bit in question is "Morse" brand, which I have found to be high quality, but this bit is just giving me difficulties.
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- Jun 7, 2013
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Yes, a little fast, rule of thumb would be about 200 rpm tops, perhaps 160 would be safer,