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Schaller Machinehead Thrust Bearing Hole Size

Discussion in 'Luthier's Corner' started by Betyouaint, Jul 6, 2012.

  1. I have a new set of Schaller bass machineheads to fit to my project bass. The outer thrust bearing diameter is 17.5mm or 11/16". Now I'm assuming that this needs to be an interference fit to hold the bearing in place and that my 11/16" bit is going to make the hole too slack? I drilled a test hole in some scrap and this is definately the case. What size bit should I be using for the Schallers...?

  2. low2groove

    low2groove Tyranis 4 / Lower Groove Guitars

    Jan 21, 2007
    The hole is positively 17.5mm or 11/16th" I build custom basses and exclusively use Schaller BML tuners in all my builds and this measurements works every time.

    Make sure your drill is not wandering off course or be sure it doesn't have a side to side wobble which would enlarge your hole. Better than a standard drill , I use a Forstner bit for this operation and it has never failed me yet.

    A drill press is also crucial to get a nice even hole through anything.

    You'll need to find one of either of these sizes on line because they are not standard in most sets. I assume you use these already forstner bits to drill out holes for electronics on bodies.

    Don't forget to use a backer board behind whatever you're drilling out so you don't get a chip or tear out on your work piece.
  3. low2groove

    low2groove Tyranis 4 / Lower Groove Guitars

    Jan 21, 2007
    A 17mm should also work just fine!
  4. ctmullins

    ctmullins fueled by beer and coconut Gold Supporting Member

    Apr 18, 2008
    MS Gulf Coast
    I'm highly opinionated and extremely self-assured
    I don't have a drill press, but I've had good luck with a sharp brad point bit, high rpms, and a steady hand. The brad point keeps the bit from wandering And yes, definitely a backing board.
  5. Thanks for the advice. I don't have a drill press so it's likely the slack is caused by drill wobble. I'd like to go with the 17mm to ensure that the bearings bite into the wood a little. I'm currently testing with a 17.5mm auger bit.
  6. Okay... Top tip: Don't buy Irwin arbor bits if you want an accurate bit size. Claimed size of 11/16 (17.5mm) turned out to be an actual size of 17.94mm. That's pretty much +0.5mm plus wobble factor, the difference between a snug bearing and a sloppy one.

    I honed the bit down to just under 17.5mm and drilled some test holes. Perfect...!!!

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