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Thread: Hole centering aid

  1. #1
    Supporting Member mklotz's Avatar
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    Aug 2015
    LA, CA, USA
    Thanked 5,227 Times in 1,740 Posts

    mklotz's Tools

    Hole centering aid

    Like many HSMs I don't have the headroom on my mill to use a coax indicator to center holes under the quill.

    If the job doesn't require the accuracy of the Zero-It indicator, I'll often just use the pointy end of the edge finder (shown at top of picture) to center the hole. Unfortunately, the larger end of the conical tip is only 0.3" diameter so one is out of luck for holes larger than that.

    If the holes happen to be aliquot sizes, a set of nesting drill bushings (shown at bottom) can help but, if the hole is slightly over/under size, the fit can be sloppy.

    I made these two devices to deal with the problem. Each consists of a slug of steel, accurately center-drilled at one end and having a conical taper at the other. Each has a companion close-fitting ring.

    In use, the cone is inserted into the hole and the ring is pressed down on the stock to ensure that the conical plunger is held vertically. Then the cone on the edge finder is inserted into the center-drilled hole.

    No, it's not as accurate as using a DTI in the Zero-It but it's more than accurate enough for 90% of the jobs I do.

    They're simple to make. Try one.

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    Last edited by mklotz; Jul 5, 2017 at 04:32 PM.
    Regards, Marv

    Home Shop Freeware

  2. The Following 10 Users Say Thank You to mklotz For This Useful Post:

    Captainleeward (Jan 31, 2018), Jon (Aug 29, 2015), kbalch (Aug 31, 2015), kngtek (Oct 31, 2017), lazarus (Jun 13, 2016), Moby Duck (Jan 23, 2018), Paul Jones (Aug 29, 2015), PJs (Sep 2, 2015), Scotsman Hosie (Jul 14, 2019), Sleykin (Mar 13, 2020)

  3. #2
    kbalch's Avatar
    Join Date
    Jun 2012
    Clermont, FL
    Thanked 524 Times in 378 Posts
    Thanks mklotz! I've added your Hole Centering Aid to our Measuring and Marking category, as well as to your builder page: mklotz's Homemade Tools. Your receipt:

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