Hi guys, first post - I did a search and could not find much on this. I work on equipment that requires removal of rusted in place 1/2-in flat head hex socket bolts or enlarging laser cut holes in steel and go though quite a few drill bits (HHS and cobalt). I am using a hand drill and use a Darex sharpener to re-sharpen the bits. I find after a number of times sharpened the bit doesn't cut as well or not at all. Either only the end of the bit was tempered or I overheated the bit and lost the temper? Would like to know if it is safe to re-temper the bits and best way to do it.
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Tempering Drill Bits
- Thread starter KAD
- Start date
- Joined
- Jan 16, 2020
- Messages
- 8
+1 on what Arkie said. Web thinning is very helpful and split point bits are the cat's meow. One of the places I used to work had a Darex drill sharpener, but I forget what model number it was. It did have the capability to make split points and I loved it, especially since most of the work I was doing there was with 316 stainless. It seemed like sharpening bits was my largest use of time during my work day!
Flat head socket cap screws are hard, and will eat drill bits, no matter what you do. Cobalt and carbide bits will work better than HSS, but they are costly.
Flat head socket cap screws are hard, and will eat drill bits, no matter what you do. Cobalt and carbide bits will work better than HSS, but they are costly.
- Joined
- Jul 26, 2011
- Messages
- 4,142
You did not mention the make of your drill bits,USA or Chinese,etc.. Some Chinese drill bit sets do not have all of the drills in the set hardened. They only harden the common fractional sizes like 1/8", 1/4",etc. They think the average home owner will only ever use those drill sizes(and they may well be right). But,it messes up us more advanced drill users.
I only ever buy USA made drills.
I only ever buy USA made drills.
Yes I noticed the web does get thicker. I'm using a Darex V390 it will split point. I sharpen to a 135 degree point and can set it anywhere from 118 to 140. My problem is drilling through the bolt head with a 9/16 bit to separate the head from the bolt shaft. I started out with a bit the same size as the hex socket straight through the bolt followed by a 3/8 bit. No problem with either. When I continue with either a 1/2 or 9/16 they will just start to cut then just ride on the steel. I think I am now out near the thin section of the flat head bolt and it is harder. Of course I then attempt pushing harder and spinning the drill as fast as it will go and probably work harden the started hole - I since have found out I should have stopped right away and re sharpened. This takes time, and I thought if I could harden the cutting edge I could get more depth. I did find some instructions on heating the end to brown/purple followed by water quench & another heat to dull red followed by water quench the re heat to dull red and slow cool - don't know if this is for HSS though. I may experiment but don't want my bits to shatter.
The bits up to 1/2 are Norseman made in US. Appear to be tin coated but will bend easily if caught in a hole makes me suspect they are not hardened for length. The 9/16 is a Dormer it's probably cut down an inch from repeated sharpening. Also tried a 1/2 Cobalt Dewalt.
Splitting the points is a good idea but thinning works the best. Slow drill speed and a lot of cutting oil should work better. Turning too fast glazes (work hardens) the material and dulls the cutting edge. It sounds like you are using hardware store auto parts drill bits.
Last edited:
- Joined
- Feb 2, 2013
- Messages
- 3,627
is it possible to heat your 1/2" screws you intend to drill with a rosebud torch tip?
you might be able to soften the bolt rather than go through a bunch of drill bits.
I'll use a air arc or gouging torch most times.
i have used arc welders with 6010 for dc machines or 6011 for ac machines, cranked up and burned heads off of bolts,
it's a crude method but very effective. the heat produced by the arc has a loosening effect on the frozen bolt . just grind off any protrusions
usually for hard stuff lower your RPM's and try to give a heavy feed rate.
i just love bacon grease mixed with 90 wt oil.
it stinks a little because of the gear oil, but it works quite well for most materials.
good luck
you might be able to soften the bolt rather than go through a bunch of drill bits.
I'll use a air arc or gouging torch most times.
i have used arc welders with 6010 for dc machines or 6011 for ac machines, cranked up and burned heads off of bolts,
it's a crude method but very effective. the heat produced by the arc has a loosening effect on the frozen bolt . just grind off any protrusions
usually for hard stuff lower your RPM's and try to give a heavy feed rate.
i just love bacon grease mixed with 90 wt oil.
it stinks a little because of the gear oil, but it works quite well for most materials.
good luck
I've never tried a left hand bit, that would rotate counterclockwise? Would that possibly cut into the started hole better after using a right hand bit? On a related or maybe unrelated note I saw something on the web about using a punch with a 4 sided point on a punch to give the bit something to grab on. Not sure if they were talking about using it for a starting punch or wacking it into a started hole.
I thought about heat but on most jobs I can't damage the surrounding painted surface and also cannot burn though the tapered hole in the plate for the bolt head since a new bolt will be installed. I'm going to experiment with spot annealing pressing a red hot rod against the bolt head. How big of a mess does the welding rod make?
I thought about heat but on most jobs I can't damage the surrounding painted surface and also cannot burn though the tapered hole in the plate for the bolt head since a new bolt will be installed. I'm going to experiment with spot annealing pressing a red hot rod against the bolt head. How big of a mess does the welding rod make?