Cobalt Drill Bits

Since diamond would vaporize or dissolve into the metal it would be best to use another super hard stone that wasn't pure carbon.
MSCdirect sells carbide drills. I used one to drill a hole into a High speed steel 1/4" square metal turning steel. Normally one would grind a shape and then cut steel with it. I drilled a hole and ground off the front - now a U and a form tool.
It was red hot and cut through nicely.
Martin
Michael Koblic wrote:

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wrote:

Carbide in a hand drill tends to get you a lot of busted drill bits. They dont take sideways bending, something very hard not to do when runnng a hand drill.
I can, after years of practice, not bust 1/8 and up, if Im very very careful. But I generally stick carbide in a drill press.
Gunner
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    Craftsman? Are you *sure* that they were real Cobalt steel? Go for Cleveland or one of the other serious US drill bit makers, not Craftsman, which could be imports from anywhere -- pseudo cobalt steel. Judge Craftsman by the difference between Sears advertised horsepower on a shop-vac or an air compressor, and the *real* horsepower determined by objective measurements.
    Second -- can you measure the hardness of what you were trying to drill? Fastener heads -- *good* ones are quite hard, especially the black-oxide finished ones, and probably would burn out most bits other than perhaps solid carbide in a rigid enough machine. (Don't even *try* solid carbide in a hand-held drill motor. :-)
    Good Luck,         DoN.
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wrote:

I have also read about but not seen Stellite drill bits - apparently these can operate red hot - maybe even orange hot, and so you just push hard and let them melt their way through the hardened whatever you are trying to drill.
for the particular application, left hand bits might be helpful because there is a small chance they can start to loosen the fasteners.
note also, anti-seize may help reduce the problem the next time
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wrote:

They're pretty much obsolete. They combine the hardness of low-grade HSS with less thermal tolerance than carbide, and with most of the brittleness of carbide. Micrograin carbides are better in almost every way, especially when you aren't using them in modern, rigid machine tools. For use in modern machine tools, other carbides may be better. For use in hand-held drill motors...I'll still stand back and watch. <g>

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    [ ... ]

    [ ... ]

    Hmm ... I've never heard about *drill* bits made of Stellite, but I have a couple of *lathe* bits (thanks to Harold Vrodos, from whom I learned about them.
    Making drill bits from that is probably as difficult as making them from solid carbide -- but they would be nice to have.

    Agreed -- but only if the shank of the screw is large enough so a reasonable strength drill bit could be used.

    Next time! Too late now. (And he probably did not have any control over how they were originally installed. :-)
    Good Luck,         DoN.
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Haven't done any chemical, spectrometric, or rockwell analysis on the bits, so the short answer would be "no, I'm not sure". Package says "Cobalt" although there are no MIL-SPECs or other grading standards listed. From what I gather above, cobalt is by degree, so I suspect these are on the fringe.
Seems they are inappropriate for the task anyway. I'm going to try the bits with a grade-8 fastener and see how they fare.

Thanks. I'm going to use valve-lapping compound on the screwdriver for more bite and hopefully avoid too many more screws that require special attention. The Dremel is the silver bullet this time.
Ernst
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Maybe an easier approach would be cutting away the broken off screws, Ernst.
There are some small hole saws for use in drills or die grinders with 1/4" collets that could be used to cut out the base metal around the frozen screw. I saw some yesterday that had diamond grit on them, but carbon steel saw teeth or carbide grit would likely be better.
Another method would be to use a piece of tubing in a drill chuck and dip it in a grit paste like valve grinding compound. May get a bit messy, but a good solvent on a rag should be all that's required for cleanup, just avoid too much rubbing.
I think you mentioned the screws were in a window frame of some sort. If there is a feature (channel or edge) that would position a guide over the screw stub (so the hole saw can't run away), make up a guide for a small hole saw that could be clamped into position for cutting out a broken screw, then repositioned over another, etc.
It shouldn't be too difficult to find something to fill the hole (push-in plastic gizzy, etc) for a new screw to anchor in.. or just fill the holes with some "miracle hole filler in a tube" and screw into that.
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On Fri, 9 Jan 2009 21:44:37 -0500, "Wild_Bill"

When I had a screw in the corner of a shower door panel with the head broken off, I was able to go through the slot in the extrusion with a Dremel cut off wheel and cut a slot through the axis of the remainder of the screw whereupon the two slivers of screw were easily persuaded to fall out. Gerry :-)} London, Canada
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Yep, a Dremel tool or similar rotary tool can save a lot of grief sometimes. A very valuable tool when they are needed.
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In article <cab8b2a4-f141-4405-874a-db516a17195a@

Coblat isn't that much harder than HSS, they just have better high temperature hardness. You might try repointing a masonery bit. Not guaranteed, but it's a lot cheaper than full blown carbide drills.
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