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Thread: Step Down drill bit

  1. #1
    Supporting Member Christophe Mineau's Avatar
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    Christophe Mineau's Tools

    Step Down drill bit

    This is a follow up of a previous post about deep drilling and especially step drilling for roughing out a conical bore :

    In this article, I explained that the best thing to do was to first establish a guiding hole with the smallest diameter.
    I used to do that with a long and thin 4mm diameter gun drill.
    Unfortunately, maybe I was too much in a hurry, but I ended up breaking this gun drill.

    So here is how I do it now :
    -1) I use a 1/4" gundrill, as deep as I can, but not all the way through.

    - 2) Here comes the new tool : I use this "stepping down" drill bit extension, in order to establish, after the 6.35 hole, a well centered 4mm diameter second level guiding hole.

    -3) If not long enough, I finish the hole with a 4mm D-bit, which is much more easy to drive at this depth thanks to the 6.35 initial bore in the first part of the hole.

    -4) I use the second setp down head to get an intermediate 5mm diameter step, between the 4 and 6.35.

    It is basically a brass extension shank, silver brazed on the shank of a standard good quality metal drill bit.
    Once brazed, I put the drill bit in the lathe chuck, and turn down the brass to 6.35 mm. Doing so, I am sure there is a perfect concentricity.
    Then I tap the end of the brass to M5, in order to screw an extension rod, which is threaded M5 at the end.

    Cheers !
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  2. The Following 4 Users Say Thank You to Christophe Mineau For This Useful Post:

    blkadder (04-30-2018), Jon (04-30-2018), PJs (05-02-2018), Seedtick (04-30-2018)

  3. #2
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    Thanks Christophe Mineau! We've added your Extended Drill Bit to our Drilling and Drill Presses category,
    as well as to your builder page: Christophe Mineau's Homemade Tools. Your receipt:

  4. #3
    Supporting Member Ralphxyz's Avatar
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    Ralphxyz's Tools
    Nice, thanks


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