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Thread: In praise of split cotters

  1. #1
    Supporting Member mklotz's Avatar
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    In praise of split cotters

    We're all familiar with this type of clamp...

    for clamping onto cylindrical forms. Effective for light loading but not the best solution to resist twisting torque in more stressful applications.

    A much more effective clamp is the "split cotter". This pdf...;attach=7950

    shows two styles of cotter clamps. The one labeled "B" is the more effective and the one that most folks envision when they hear the term "split cotter".

    Frank Ford, a prolific contributor on this forum, has described the making and use of a split cotter on his personal web page...


    A good discussion of split cotters and their design is given in pages 92-96 of Lautard's The Machinist's Bedside Reader (that's the first volume of his three volume series).

    Aside: All three of the MBR series are worth adding to your shop library. Guy's website is here...

    Guy Lautard.Com Machinists Books & Supplies: Lathes, Milling, Drills, Gunsmithing and Clock making

    Sadly, all the MBRs are currently out of print, though he promises to bring them back.

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    Regards, Marv

    Home Shop Freeware

  2. The Following 5 Users Say Thank You to mklotz For This Useful Post:

    Frank S (Jun 8, 2018), JD62 (Jun 8, 2018), Jon (Jun 8, 2018), Seedtick (Jun 8, 2018), Toolmaker51 (Jun 8, 2018)

  3. #2
    Supporting Member metric_taper's Avatar
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    I just made 2 conventional clamps for my wife's long arm quilting machine. The existing laser pointer had failed to where its brightness required the room to be darkened. As an OEM replacement was over $70, I ordered a replacement bare diode from an eBay seller (received 10 of them). I made a holder for the bare diode from 1 inch Delrin round stock (served as an electrical insulator). The machine has a 1/4 inch (actually .242") mounting rod (which explains why there are 2 holes on that clamp, note to self; don't guess, measure it first).
    In praise of split cotters-img_20180608_200343.jpg

    In praise of split cotters-img_20180608_200349.jpg

    I used a roll pin to pin the main bolt (1/4x20 2.5 inch long) in the small clamp. I cheated and used a COTS (commercial off the shelf) wing nut vs making a knurled disk like the original.
    In praise of split cotters-img_20180608_203906.jpg

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    Last edited by metric_taper; Jun 9, 2018 at 07:05 AM.

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