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I have a metal part of a bandsaw that had a machine screw head break off. I drilled a hole and used an extraction bit and it also broke off. Due to poorly executed attempts to drill again (so I can tap it), the surface is now irregular enough that the bit (and chuck) of my drill press wobbles out of place. I thought I might melt the surface to level it out, but the Propane torch I bought doesn't seem to get hot enough (after 3 minutes of leaving the flame on the metal). I contacted a couple machine shops and they aren't interested in this tiny job. Any suggestions on how I can get a centered hole drilled in this thing? Also, should I be trying to drill a larger hole than was there, since the integrity of a same size hole would be affected by the previous hole?

Edit: You can see the part [here][1]. It is 2 5/8" long. The one I have is steel; the potential replacement is not exactly the same shape and appears to be soft metal. It would be over $50. (I've spent about $40 so far trying to fix it.) The problem area is the rightmost screw hole in the photo, which is currently filled with metal from the top to about 80% of the depth of the original hole. There is no access to it from the other side. (The bit would have to cut through metal on the far side of the bit and air on the near.)

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  • Well, that's a mess.. now it sounds like you have a bit of hardened tool steel right in the middle of where you want to drill, which you may or may not have taken some of the temper out of while playing with the torch. (Probably not.) At this point I would suggest you take time out to check how much the manufacturer would want for a replacement for that part.
    – keshlam
    Commented Aug 30, 2015 at 18:13
  • Propane alone won't heat the metal to a high enough temperature. You need to add oxygen to the fuel. Look for the smaller canisters at a Home Center. Pick-up some brazing rods to fill opening.
    – ojait
    Commented Aug 30, 2015 at 18:52
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    You could also inquire at any muffler shops in regards to welding repairs.
    – ojait
    Commented Aug 30, 2015 at 18:54
  • Hrm. The Internet says a propane-air mix burns at 1995 C and steel melts at 1510 C. I figured this temperature difference would be enough for it to melt. Are they talking about an in-nozzle mix with compressed air? What have I failed to understand about melting the surface to remove irregularities in the shape?
    – user41984
    Commented Aug 30, 2015 at 22:33
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    When a drill bit won't cut through, it's often useful to switch to an aluminum oxide grinder bit and bore through the piece while wet. Sometimes you'll have to go to diamond, but sapphire will take care of most steels. Always go slow enough to let the water keep the piece cool. Hot sintered binders have a nasty tendency to fracture.
    – Wayfaring Stranger
    Commented Aug 31, 2015 at 20:36

3 Answers 3

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First try to determine if the piece is a solid piece of steel or a casting, sometimes referred to as potmetal. Over heating a casting can turn it to a brittle paperweight The broken extractor bit is likely to hard to drill out. If you have access to the opposite side try to drill a small hole and drive the broken extractor out with a punch. Once the broken bit is removed drill and tap it for a larger screw, install a heli-coil or a nutsert.

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Silly me for assuming that the part I needed to attached to this damaged piece was machined correctly. It turns out they had it in backward when they made it, so I drilled new holes in both pieces (which I found out I am really bad at), and the screws (nevertheless) hold it together now. Thanks all for your ideas!

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Good idea about trying to fill the hole. You need an oxy-acetylene torch to heat it enough for brazing to flow. Or a stick welder. Is it a viable option to attach a repair piece of stock on top and over the damaged section. Something that overlaps enough so it can be : screwed, bolted, welded... into position? Than drill and tap.

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  • I thought of this and it still appears to be my best option. The problem is I wasn't able to come up with a repair piece of stock that would work. I tried drilling a piece of aluminum, but it was too soft, and the side of my bit gladly chewed through it. However, I'll look around for something harder I could drill.
    – user41984
    Commented Aug 31, 2015 at 11:36

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