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Can I gain a few thou by shimming one side of a drill bit

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  • Can I gain a few thou by shimming one side of a drill bit

    My 5/8 Tap won't fit through the 5/8 hole I drilled through a tap guide I made, the tap wants to thread the die but I want it to freely pass through the guide. Instead of buying larger drill bits, I have different sizes of brass shimstock, can I safely place a piece of shim stock on one side of my 5/8 drill bit to gain the few thou i need? Thanks

    I have collets for my mill, would a collet be better to hold the shim and drill bit?
    Last edited by tackit; 03-04-2018, 12:37 PM.

  • #2
    If and when the hole is less than smooth the brass is either going to wear out very fast or the drill is just going to cut trough it.
    Location: Helsinki, Finland, Europe

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    • #3
      Originally posted by MattiJ View Post
      If and when the hole is less than smooth the brass is either going to wear out very fast or the drill is just going to cut trough it.
      Matti, the hole has been reamed.

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      • #4
        I'm not understanding. Are you wanting to re-drill your guide? Are you intending to shim the cutting end of the drill, or the shank? If you're going to make a new guide you can just intentionally grind your drill a bit asymmetrically and get a larger hole. Can you not bore the hole a bit on a lathe or mill?
        Southwest Utah

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        • #5
          Sharpen the drill bit with one lip a little longer than the other.

          To get a drill bit to cut close to the nominal size, you need to get the two cutting edges the same length or else the bit will cut over size. So you can work this idea in reverse - the point of the drill bit will be in the center of the hole - if the center is off a bit, the hole will be oversize. Obviously, within reason (0.02" over on a 0.625 hole should be no problem).

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          • #6
            Hone it.
            If you benefit from the Dunning-Kruger Effect you may not even know it ;-)

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            • #7
              Why doesn't your tap fit? Is the tap not to spec or your reamer undersized?

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              • #8
                Originally posted by craigd View Post
                Sharpen the drill bit with one lip a little longer than the other.
                Yes, unless he's attempting to enlarge an existing hole. Then it doesn't work.
                Southwest Utah

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                • #9
                  sounds like the perfect job for an expanding reamer!

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                  • #10
                    If you don't have an oversize reamer, you may try plugging one flute of your 5/8" one with something like a toothpick. It'll cut oversize. I assume the drill guide wasn't hardened yet, of course.
                    Last edited by MichaelP; 03-04-2018, 01:46 PM.
                    Mike
                    WI/IL border, USA

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                    • #11
                      Ok. With your edit about using collets, I suspect you're considering shimming the shank like you do an endmill to make it cut oversize. It will not work with a drill. It only works with an endmill because that tool is rigid enough to maintain the oscillating orbit throughout its length. The drill will simply flex and the point will follow the punch mark or pilot hole. You still haven't clarified whether you are trying to enlarge the first hole or start over. The options vary.

                      There is nothing practical you can do with a drill bit to oversize an existing hole except use a larger bit. Attempting to pack the flutes is an exercise in frustration. The packing is impossible to gauge, (you might get .0005" or .005" or nothing at all) it tends to wear quickly or fall out. If you've nothing but time and your blood-pressure is low, go ahead and try it.
                      Last edited by chipmaker4130; 03-04-2018, 08:04 PM.
                      Southwest Utah

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                      • #12
                        Originally posted by lakeside53 View Post
                        Why doesn't your tap fit? Is the tap not to spec or your reamer undersized?
                        tap OD's are usually (often? always? supposed to be?) slightly more than nominal. Drill it 16MM, if that's not enough to give some clearance 1) use a boring head, 2) bore it in the lathe, 3) jam something soft (wood/rag etc) in the flutes of a 5/8 reamer or what I'd do, use an adjustable reamer.
                        in Toronto Ontario - where are you?

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                        • #13
                          I learned a trick on this forum several years ago for just this kind of situation. Stuff a rag in one of the flutes and shoot it with some oil. It will cut slightly oversize. Or buy an adjustable reamer.

                          Oops... Mcgyver beat me to it. Come to think of it, he may have been the one who taught me the trick in the first place...?
                          Last edited by Fasttrack; 03-04-2018, 01:37 PM.

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                          • #14
                            Put the tap in the mill, or drill press (probably not a hand drill, that could be bad)..

                            Spin it up, and use it like a reamer.. Your only pulling out a couple of thou, it *shouldn't* grab and
                            pull, hopefully, if you take it easy and pay attention.. Or come up from the bottom.

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                            • #15
                              Originally posted by MichaelP View Post
                              If you don't have an oversize reamer, you may try plugging one flute of your 5/8" one with something like a toothpick. It'll cut oversize. I assume the drill guide wasn't hardened yet, of course.
                              I was going to suggest much the same thing. Pack one of the flutes to push the drill a bit to the side. But on a 5/8 drill it's going to take using a toothpick sized for an elephant....

                              I'd say trim a bit of dowel that more or less sits in the flute decently well into a "D" shape that puts pressure on the wall and sticks out a little. That should force the opposite edge into the wall a little.

                              But then there's also the idea of simply setting it up in the lathe and bore it out a hair.
                              Chilliwack BC, Canada

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