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Drill bits for gun steel?

Discussion in 'Gunsmithing and Repairs' started by GI_Jared, Jan 12, 2012.

  1. GI_Jared

    GI_Jared Well-Known Member

    I am in the process of turning a Troy Claymore muzzle brake into more of a flash suppressor. The brake is made of very hard steel and is a real bitch to drill through. I was currently using a Lawson 1/8" pure carbide drill die bit, but then I broke it because I was going to fast and not using enough oil. I was wondering if there is any other bit that might be better for this task before I order another one, they are like $15 a piece.
  2. rjrivero

    rjrivero Well-Known Member

    Coolant. Troy breaks are hard steel. If you recirculate coolant on the work piece, it'll make your drill last longer.
  3. rcmodel

    rcmodel Member in memoriam

    Maybe try annealing it?
    It doesn't have to be that hard.

    Unless it is air hardening steel, heat it red, then cool it slowly and it should be annealed enough to drill with any drill bit.

  4. exospex

    exospex Well-Known Member

    Sometimes a carbide drill is not the best answer. They are very brittle and do not like shock at all. I'm guessing that the break is not "glass hard" I'd guess somewhere in the 37-39 Hrc range. A good quality cobalt split point screw machine length drill should do the trick. You will want to run it at about 25 SFM, so that's about 750 rpm. feed real easy and plenty of oil. you will want to start every hole with a spotting and centering drill. You will get away with carbide for that and it will help you get through the harder "crust".

    Good luck.

  5. exospex

    exospex Well-Known Member

    I just thought of something else. If you smoke out the cobalt bits. Try a solid carbide die bit like this Spade bit same rules, go slow and plenty of oil and lots of pecks so you don't chip pack the flute.
  6. james layman

    james layman Well-Known Member

    drill bits for gun steel

    GI, Something a master smith showed me. Heat a bit cherry red, dip it in a solution of salt water. For some reason it gets harder. I used this procedure to tap receivers for scopes, tempering both bit & tap. Be sure to wear eye protection any time you drill. A drop of oil may help to cool. Let us know how you make out. Jim
  7. 1stmarine

    1stmarine Well-Known Member

    Cobalt bits work well for me. go slow so you do not burn them.
  8. GI_Jared

    GI_Jared Well-Known Member

    So I have already tried good cobalt bits and they will not even start drilling into the brake. I may order a one of the spade style bits and one of the two flute carbide bits and see which one lasts longer. I will also try to harden the bit with the heated salt water method.

    I won't be able to work on this again till Monday, so I will double check my rpms and make sure they are up around 750. I think it is set around 350 right now which would make a lot on sense of why the bit caught and broke right as it was breaking through.

    Thanks all for the advice, i'm pretty much a newbie when it comes to gunsmithing. I'll post some more pics when I make more progress.
  9. nyresq

    nyresq Well-Known Member

    TiNi coated bits have worked well for me for case hardened steel and stainless... go real real slow on the slowest speed you can get the press to adjust to; and a constant flow of coolant is absolutely required. Go slow, real slow.

    you could also try annealing the break before you drill it. Never tried it, but its worth a shot and there is no need to have a super hard steel for the muzzle break.
  10. Old Dog Man

    Old Dog Man Well-Known Member

    Hard steel muzzlebreak

    Heat the break untilll it's red in color, then put it in lime overnight to cool then it can be drilled. ai use cobalt drills. Al
  11. GI_Jared

    GI_Jared Well-Known Member

    How much strength is lost by heating up the brake and will it mess up the threading? Also, what is the purpose of the lime? Is it just to provide a safe place to evenly cool or is it something else?
  12. CCW1911

    CCW1911 Well-Known Member

    With something hard like that set up is very important. It would be much better to drill it set up in a solid vice on a milling machine. Vibrations dull drill bits quickly and is death to solid carbide tools. Sometimes I've used a carbide end mill instead of a drill bit but like I said you have to have a very solid set up.
  13. doubleh

    doubleh Well-Known Member

    Lime makes it cool slowly. You can do the same thing with dirt, ashes, or kitty litter. I anneal old files to make knives and stick them a bucket of sand and let them cool over night. They are softer than cold rolled mild steel then.
  14. brickeyee

    brickeyee Well-Known Member

    Metal drilling usually goes a lot better with some lubricant.
  15. Old Dog Man

    Old Dog Man Well-Known Member

    Anneling hard metals

    Anneling the metal will not weaken it to the point that it will fail as a muzzlebreak. I've seen them made from aluminum (not me) but they seemed to be ok. I've annealed allen wrenches and car springs to make parts with, using the heating red and cooling in lime overnight method since the early 60's and it still works today. Al
  16. Chris-bob

    Chris-bob Well-Known Member

    Judging from the pic you posted, I'd say the problem lies partially in your vise. It is not set up for holding a round object. If the object can move even the tiniest amount, you can shatter carbide bits no matter how slow you go and how much coolant you use.
  17. Clipper

    Clipper Well-Known Member

    Try to pick up a carbide 2-flute ball-nose end mill. It will cut through hard steel, and leave less of an inner burr than a drill. spin it fast, 1000 RPM or so, and take small pecks to clear chips and minimize heat buildup.
  18. GI_Jared

    GI_Jared Well-Known Member

  19. james layman

    james layman Well-Known Member

    drill hard metal

    My memory is fading, but i seen a revolver hammer heated and dipped in to carborundom a grainly like substance. It left a rough surface. It had to be polished down. It left a smoothe mirror like finish. Leaving no drag on the trigger pull. I suspect a broken bit could be restored. I don't know if carborundom, brand name, is available. If it is, it probably would cost an arm and leg. You probably don't know if creating a flash suppressor will be effective. Why don't you try a new less expensive one. Let us know what you come up with. James

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