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Great Drill Bits for plastic

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  • #16
    Originally posted by nickel-city-fab View Post

    No, it really does work I had to learn that one the hard way. Ever try drilling in copper without grabbing, you have to dull off the edges a bit with a stone.
    As in actually dull them? I have to admit that I've only drilled copper a couple of times. And other than some thin sheet it was with these brass and plastic modified drills which did pretty well in copper as well.

    A place where altering them over to a neutral or slight negative rake would be almost a must is for drilling any counter bores in plastics. With anything other than a mill or drill press with a depth stop set it's going to be very difficult to avoid the drill grabbing and pulling into the cut very aggressively when there's no center pip riding on the material to at least hold it back a little. And even with a depth stop it'll be a wild ride until the stop is reached..... Bented's claims notwithstanding.

    Chilliwack BC, Canada

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    • #17
      Originally posted by BCRider View Post

      As in actually dull them? I have to admit that I've only drilled copper a couple of times. And other than some thin sheet it was with these brass and plastic modified drills which did pretty well in copper as well.
      Well, maybe "dull" wasn't the best word to use, but yeah. I take a small India stone and scrub the sharp edge off the cutting edges before I try to drill copper, brass, and plastics. If I need a bit to stay sharp for steel, then it stays sharp and the brass/copper/plastic bits go into a separate box.
      Especially, trying to drill (enlarge) the hole in a copper washer can be a huge PITA without grabbing warping and marring the surface.
      25 miles north of Buffalo NY, USA

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      • #18
        By stoning the cutting edge you are putting on a neutral or negative rake which helps break up the chips just like the rake on indexable drills.
        John b. SW Chicago burbs.

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        • #19
          Originally posted by Paul Alciatore View Post
          Changing the rake angle on a cutting tool does not mean it will be dull. There are many inserts that have a zero degree rake and even negative rake angles. They are still quite sharp.




          Indeed, I normally use high negative rake tooling for turning, if my employer had purchased an inserted drill of the correct size I would have pushed the feed and speed way up, there would be no sharp edges to fail.
          A very sharp edge is asking for tool failure, a nice .002" radius on the cutting edge is excellent.

          This insert has no sharp corners, these will bang out nicely finished stainless parts all day long.
          Last edited by Bented; 07-16-2021, 04:34 PM.

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          • #20
            Originally posted by Paul Alciatore View Post
            Changing the rake angle on a cutting tool does not mean it will be dull. There are many inserts that have a zero degree rake and even negative rake angles. They are still quite sharp.




            That always irritates me greatly when people call changing the rake angle "dulling" . It's almost as bad as using the word "billet" . :-)
            ...lew...

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            • #21
              Originally posted by nickel-city-fab View Post

              Well, maybe "dull" wasn't the best word to use, but yeah. I take a small India stone and scrub the sharp edge off the cutting edges before I try to drill copper, brass, and plastics. If I need a bit to stay sharp for steel, then it stays sharp and the brass/copper/plastic bits go into a separate box.
              Especially, trying to drill (enlarge) the hole in a copper washer can be a huge PITA without grabbing warping and marring the surface.
              Yeah, if you're holding the stone at a set angle rather than rolling it you're stoning on the same sort of rake angle flat but still with a sharp edge as I showed in the picture a few posts back. It would only be actually dulling the edge if you rolled the stone to produce a rounded edge. So I'm suspecting same thing but smaller.

              For smaller sizes I use a stone file same as you're doing simply because it's hard to get into the smaller sizes with a grinder. But it's still a specific angle to get a neutral to just few degrees negative rake angle and keep a sharp "scraper" edge.


              EDITED TO ADD-

              From Bented;
              This insert has no sharp corners, these will bang out nicely finished stainless parts all day long.
              But as others and myself have proven to ourselves such cutters with that sort of cutting edge shape need very sturdy machines and have to cut with fairly specific speeds, feeds and DOC. The deliberately soft edges cause a lot of pressure compared to classically sharp edges.


              Last edited by BCRider; 07-17-2021, 02:49 PM.
              Chilliwack BC, Canada

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              • #22
                Well, I'm sure that my stoning on a drill bit is not that accurate, so i hesitate to call it a "negative rake angle" as if I put it there on purpose
                more like dumb luck. So I call it "blunting the edge"
                25 miles north of Buffalo NY, USA

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