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Twist Drill Bit Geometry ?

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  • Twist Drill Bit Geometry ?

    Ok, This might sound like a dumb question but after thinking about it fer a few miniutes I cant figure it out. Why are drill bits flutes sharpened?
    I understand end mills cut on the sides as well as on the end. But drill bits only cut on the ends (118 degrees). Now insert carbide tipped drill bits only have sharpe edges on the 118 edge, not the flutes. Masonary are the same way.
    Whats the purpose of sharp flute edges?

    I know, I know you can wobble the hand drill and make the hole alittle bit bigger.... But that aint the answer.......

  • #2
    Clearance to elimiate rubbing and eventual heat build up then failure.

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    • #3
      They are only sharpened on the ends.

      Consider how the chips are formed.

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      • #4
        It seems to me that's the best way to get the drill to fit the hole close enough to cleanly bring the chips out and to be able to also help clean up any roughness left by the cutting lips. I feel pretty sure the drill would otherwise easily jam in the hole.
        Don Young

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        • #5
          I don't think they're deliberately sharpened, I suspect they end up sharp by default when the flutes are milled.
          Newtown, CT USA

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          • #6
            agreeing with Don. First, if those edges weren't sharp there would be no way to sharpen the cutting lips right to the edge, and second, they shovel the chips out. If they were rounded in any way, the finest of the chips would tend to jam between the sides of the bit and the hole.
            I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

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            • #7
              I believe they are just left sharp after milling, I have a set of drills thats not too sharp on the top of the flute.. But deadly razor sharp on the bottom, Figure that one out.
              Play Brutal Nature, Black Moons free to play highly realistic voxel sandbox game.

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              • #8
                Originally posted by darryl
                agreeing with Don. First, if those edges weren't sharp there would be no way to sharpen the cutting lips right to the edge, and second, they shovel the chips out. If they were rounded in any way, the finest of the chips would tend to jam between the sides of the bit and the hole.

                I think that darryl has it. If the edges of the flutes were rounded, then chips would wedge in there and cause friction and score up the hole a lot more than it is with the sharp edges. With a sharp edge there, it will tend to sweep the chips away from the sides and up the flute. It doesn't always work out perfectly, but a sharp edge here is definitely better than a dull one.
                Paul A.
                SE Texas

                Make it fit.
                You can't win and there is a penalty for trying!

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                • #9
                  i think theres clearance as well, you know back rake as well as a cutting edge
                  unless its a straight flute d bit
                  mark

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                  • #10
                    Hummm ok. Points taken... I'm sure ya all can find something of interest in here:
                    http://www.hnsa.org/doc/pdf/machinery-repairman.pdf

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