I've got an aluminum drill jig with 1/2" holes that I want to keep from being damaged during the drilling the workpiece bit. To that end, I'm thinking of making a drill bushing out of a 1/2" Grade 5 or Grade 8 bolt. An American made one fwiw. Plans are to spin the hex off, cut the threaded portion off and center drill 3/16". The 'hat' (old hex section) will keep it from dropping through and the 3/16" size is for a pilot hole for the eventual 1/2" size hole. I'd like to harden the ex-bolt now a drill-bushing a bit and the plan is to heat it to a dull orange and toss it into a bucket of water. If it's overly brittle it won't hurt since the idea is to forestall wear and not much strength is required. I know I should use drill rod, but I haven't seen the stuff since I moved and you can't buy it locally. A reasonable plan on the hardening bit? Or should I use the bolt as is vis a vis the hardening? Geezus, sometimes I think there's a poltergeist living in the garage. I'm pretty organized, but things keep disappearing. Latest was a 6" x 14" x 1/4" piece of stainless which was a touch costly. It disappeared during a project which has to be put to the side until it's found. It's probably in the same place as the fuel cell caps, a pair of spotlights, a few tools and some other stuff....
You got a lock on the shop door? I don't know about the heat treat method you describe, might make it too brittle, IIRC most of the gun smithing supply houses have a case hardening compound. You would pack it in the hole you made and heat it per the directions (that the compund should come with). It should leave the rest of the metal as ductile as it was to start with. Of course if you're like me, you need this today, so that won't help.
I know about Casenite - think that's the name - but if I can get the bolt hardened without it, that's what I'd like to do. No big rush since the stainless piece is gone. I have annealed Hurst Shifter arms by heating to a dull orange and letting cool naturally. After filing the rectangular mounting hole larger, I heated it to a dull orange and tossed it into a bucket full of water. It ended up hard as before and it may have been overly brittle, but it never gave me a problem. More than likely no heat treat on the bolt/bushing would do it since the pilot drill (3/16") isn't too large and with ten holes to drill wear shouldn't really be a problem. Anyway, if the hardening bit would work I'd take the few extra minutes to do it....
Some steels want to be quenched in water,others in oil,and others in air. If you can't buy the proper drill bushing,or material to make one, I would do a test piece first,to test the home hardening idea.
Maybe I'm missing something here, but wouldn't it be easier to buy some drill bushings and a counterbore? You counterbore your drill jig so that you can press in the drill bushing. The drill bushings would hold up much better than the bolts you're talking about using, plus you'd have a really nice jig that would stand up to lots of use.
Heat treating is a complex science. I wouldn't expect to get the desired results on the first attempt. Here's a link to some info. Scroll down to item #7 for heat treating. http://www.key-to-steel.com/default.aspx?ID=Articles
Mcmaster.com has drill bushings,around $12 each. I like the "removable drill bushing with head". They are held in place with a screw,instead of relying on a press fit. That way,they never come loose. If a local industrial supplier handles Carr-Lane,they can get them too.
Real metallurgist answer here. Most bolts are made from cold heading grade steel, such as 1022 for example if my memory is still working. They are cold formed tp make the head and shank. The Grade 5 are just left as-is, the grade 8 are heat treated. Both are typically rolled threads after heat treat or cold heading. Now your question on home heat treating. Since your carbon content should be less than 0.4%, you can water quench it. It should not crack. Higher carbon needs slower quench and oil is used, to prevent cracking. You need to get the bolt a bright red to even orange color. About 1550 F will do. After quench it really should have some tempering, but since you want real hard and not worried about brittle it may work as-quenched. Tempering is harder to do at home, you need 400F rqange for about 2 hours, maybe toss them in the oven when your wife is baking something???? Tempering just helps make it less like glass. A file is an example of something that is very hard and brittle, which is what your bolts will become similar. You will probably not have much distortion problems since you will have fairly thick walls vs length. Worse case is you try it and have to either scrap them or they will be too tight on the bit due to distortion. Jay or others with metallurgy questions, PM me if you have any other questions or need more details, i do not get on here as much as i used to due to time constraints. I could very well miss your question.
Why remove the bolt head? That makes it real easy to swap out when it wears. You could potentially make them by the dozen and if they don't wear like a proper drill bushing who cares?
I hardened the frizzen on my flintlock in the fireplace. Didnt have a crucible so I just buried in the embers for a while. The way the old timers would do it was in a crucible with bone and leather fragments. Mine worked just as well. I believe I just let it air cool.
If your are opposed to buying the bushings from McMasterCarr you can easily case harden it by heating to around 1500f and quench it in used motor oil. Use used motor oil simply for the carbon content.
If you can heat it in a carbon rich environment, like coals or leather fragments, it will encourage carbide formation at the surface. Carbide equals hardness
Known as carburizing. The carbon diffuses into the surface, but will take holding at heat for approx 2 hours to do any significant depth of carbon into the surface. Carbon does make it harder on the surface. Gears are a common application for carburizing, hard surface for wear, and a more ductile core to handle the shock loads.
I have a few transfer punches that I made out of 4130 as well as one that I made from mild steel that I simply ran an acetylene flame over while it was red hot and then re-heated it untill the carbon was gone, then I water quenched it. It worked perfectly for what i was doing. I did make sure that the parts were pretty damn smooth before I "case hardened" them to eliminate the chance of cracking as much as possible. I did try to quench the mild steel part without the acetylene soot, but it did not harden. The soot trick worked.
I am not a mettalurgist or really know a hell of a lot but when I need a quickie drill bushing I just take a brass fitting with pipe threads and tap and tighen it down in the fixture. Then drill the brass for the guide . It seems to last me a long time,I think the brass is hard enough to not get tore up by the drill bit. Hope this helps.
Thanks for the info guys. Much appreciated. I have a genuine drill bushing coming so that helps. Now, if someone could tell me where the cotton-pickin' piece of stainless went to....
The Jalopy Journal
