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How I make my own drill bits - how do you make yours?

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  • How I make my own drill bits - how do you make yours?

    I posted up a shop made spade drill in the "Shop Made Tools" thread and someone expressed interest in seeing details on the process I use to make them. I went a little picture crazy so I figured I'd start a separate thread and at the same time get feedback from anyone else here who makes their own bits, I'm really curious to see how others do it.

    I found myself needing to drill and tap a hole for M4x0.7 threads, so I needed a 3.3mm drill. This is the smallest I've made so far (I'm sure I'll make much smaller ones at some point), and the hole needed to be rather deep. I usually make my bits as short and stumpy as possible for the immediate need I have, to keep them as strong as possible.

    I started off with some O1 drill rod, and for this sort of size it made sense to fire up the watchmaker's lathe:


    I start by turning the point taper and the major diameter (3.3mm in this case). I don't get too fussy about the angle of the point - I typically go with a 60 degree included angle:


    This pic is really crappy but if you squint you can make out a slight taper turned up. I usually go for about 1 degree of taper up to what will be the shank. In this case, I will have a sort of double shank. The smaller shank, where the 1 degree taper ends, is smaller than the cutting diameter, so that I can drill deeper. A larger diameter shank, for chucking, will also be left.


    I extended the work through the collet a bit and left the diameter of the stock for the larger shank (so this drill bit is no more accurate than my collet, which is perfectly acceptable in this case). I love parting on this little machine:
    Max
    http://joyofprecision.com/

  • #2
    Let the filing begin!


    I start by filing a flat up the tapered portion:


    Then I file a flat exactly opposite the first flat:


    Now I blue up the remainder of the outside diameter, in preparation for filing relief angles:
    Max
    http://joyofprecision.com/

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    • #3
      The blue makes it easy to creep up on the relief without losing anything from the outside diameter. I file until there remains just the faintest trace of blue... this tiny amount allows for sharpening after the bit is hardened. Here is a pic showing the relief filing in progress:


      Here is the bit after all filing is completed:



      Heat treating O1 is pretty easy so I'll just mention that at this point I harden the bit, sharpen the cutting edges with a stone slip, then polish the remaining surfaces to observe the color change while tempering. I temper to a light straw color.

      Here is the completed drill bit, ready to go to work after a pilot has been drilled:
      Max
      http://joyofprecision.com/

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      • #4
        Part way through drilling, so far so good! I always use Tap Magic with these spade bits - they cut smooth as silk with it. I recommend using some sort of cutting fluid or oil, they don't really seem to like being used dry.


        Here we have the bit and the nice tidy hole it left in my part:
        Max
        http://joyofprecision.com/

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        • #5
          Thank-you. This has definitely been filed away for future reference.

          J

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          • #6
            Excellent post Mars, your description of this most useful item of tooling, I have noted as well Thanks for posting. your little watchmakers lathe is like my Boley always a treat to use

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            • #7
              Wow, wow, and more wow!!!

              Mtw fdu.

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              • #8
                Excellent posting and pics!! Thanks for this.

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                • #9
                  That's pretty much how I make mine except for the taper. I just make them straight. I cut the relief angles on the mill in an indexer, harden, then lightly touch up on a grinder. Mostly i make them to drill brass.

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                  • #10
                    Thanks for that! I do have a question. Is the bit triangular (or tri-lobal) after the relief is filed?

                    Comment


                    • #11
                      Originally posted by TheAndroid View Post
                      Thanks for that! I do have a question. Is the bit triangular (or tri-lobal) after the relief is filed?
                      Nope, it only has 2 cutting lobes - it is typically referred to as a spade drill. If you are familiar with pivot drills used in watchmaking, or with those small circuit board drills, they are the same shape.

                      Triangular drills are a neat idea though, if anyone here has tried it I'd love to hear about it.
                      Max
                      http://joyofprecision.com/

                      Comment


                      • #12
                        Thanks for the picture and details, I now have a copy in my tricks box.
                        Cheers!
                        Phil

                        Comment


                        • #13
                          I can understand why you need relief on the end cutting edges, but why bother with filing relief on the sides? The sides don't cut, much less rub, because you already have some back taper from the turning operation. (That happens automatically as a result of turning a relatively long unsupported length - the outermost end deflects away from the tool the most, and therefore ends up the fattest. This happens all the time in turning.)

                          Comment


                          • #14
                            Originally posted by rklopp View Post
                            I can understand why you need relief on the end cutting edges, but why bother with filing relief on the sides? The sides don't cut, much less rub
                            I like having a cutting relief just above the point taper, I believe it gives a little nicer finish just based on my own experimentation. Given that, it's a lot easier (for me, at least) to just file relief along the entire taper than try to get the relief just above the point taper where I want it. It's only a few extra strokes of the file in an operation that only takes a few minutes once you've done it a couple times. I'd wager that anyone omitting the relief along that taper would still be perfectly happy with the results, for sure.

                            On a related note, if you care to form the angle where the point taper meets the shallow taper going up to the shank, into a slight polished radius, you'll find the finish comes out super nice.

                            Originally posted by rklopp View Post
                            because you already have some back taper from the turning operation. (That happens automatically as a result of turning a relatively long unsupported length - the outermost end deflects away from the tool the most, and therefore ends up the fattest. This happens all the time in turning.)
                            For my purposes, I want more of a taper than the barely perceptible amount left from turning (for what it's worth, I measured less than 0.001" difference from the unsupported end up to where the chucking shank started, after turning the major diameter) as I find it makes quite a difference for clearing chips. In my experience these spade drills will clear chips pretty nice with about a degree of taper. If you don't mind withdrawing it to clear chips more often, then a nigh imperceptible taper would suffice. The chips produced by the bits I've made are always really long, thin, and stringy and just the clearance provided by the flats doesn't seem to be sufficient to keep the bit from wanting to bind up without more frequent withdrawal of the drill.

                            I'm not one for discouraging anyone from experimentation - that's how I've learned most everything... I would encourage anyone interested to experiment with making some of these on their own. You may be surprised how quickly you can knock them out, and how well they work.

                            For an alternative to these spade bits, there are also "D" bits. I haven't made any because they're basically the same as the set of jewelling reamers I already own. They're stronger than spade bits, and I think most of us would prefer to call them reamers than drill bits. You'd follow the same steps for turning the blank, then file away half of the tapered portion (so looking at it dead-on from the end, the cutting portion would be a D shape). I've come across some detailed info on making these online - I reckon a Google search would turn it up, for anyone interested.
                            Last edited by mars-red; 11-27-2012, 02:20 PM. Reason: Added details regarding chip clearing
                            Max
                            http://joyofprecision.com/

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                            • #15
                              Thanks for the detailed instructions!

                              Hi Max,

                              Just thought I'd pass on a tip for anyone who might not be aware if it. Not a drill but this will work just as well on drills.

                              If you need to keep scale from forming during your heat treating, you can use silver solder flux. You just have to be careful not to overheat it.

                              Here is how I use it to heat treat O1 steel that I cut a clock pinion from. I set it up in the drill press at slow speed w/stop set to just plunge the pinion into the oil when it is glowing bright red.





                              In this case, I had to heat the teeth hotter than I would have liked to get the heat past them & into the arbor. It just made the flux a bit harder to scrape off. Normally it will just fall off.



                              The right side of the arbor shows how clean it will stay after hardening.
                              Last edited by jhe.1973; 10-31-2017, 10:13 PM.
                              Best wishes to ya’ll.

                              Sincerely,

                              Jim

                              "To invent you need a good imagination and a pile of junk" - Thomas Edison

                              "I've always wanted to get a job as a procrastinator but I keep putting off going out to find one so I guess I'll never realize my life's dream. Frustrating!" - Me

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