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Forstner Bits or (Maybe I Suck at Math)

Discussion in 'Luthier's Corner' started by Luke Sheridan, Jul 19, 2005.

  1. Luke Sheridan

    Luke Sheridan Commercial User

    Dec 30, 2004
    Yonkers, NY
    I build guitars and sell them. Strings, too
    I measured my tuning peg holes off an 8-year old Warmoth jazz neck using a circle template and the hole is 21/32. The collar fits snugly with that dimension. 11/16 is too large. I have looked everywhere online (well, 2 Google pages worth of sites) but cannot find a Forstner bit with 21/32 dimensions. this is like 16.662mm, Will a 17mm be too large?

    Please help.
    I cut math class to often back in the day..
  2. I've never installed fender style tuning machines, but at least on gotoh, ultralites and sperzels, the whole doesn't have to be 100% acurate. It can be a tad smaller. I think fender styles don't use a threaded nut on the face of the headstock, but rather a push fit bushing.
  3. Measuring with circle templates may not be accurate, because the ones I used when drafting by hand (years ago) were oversize approx 0.5 mm to allow for the drafting pencil.

    Can you get some digital calipers instead?
  4. Remember also that the ferrules on those tuners have serrated edges that wedge into the end grain of the wood. The actual proper size of the hole would be closer to the of the ferrule measured from valley to valley across the ferrule and not peak to peak as one would do with calipers grasping the ferrule. That's definitely splitting hairs but it gives you an idea of the range of error you could have. My suggestion would be to use the same size Forstner bit that matches the holes used in Warmoth headstocks as shown on their website. They publish that dimension all over the place.
  5. Luke Sheridan

    Luke Sheridan Commercial User

    Dec 30, 2004
    Yonkers, NY
    I build guitars and sell them. Strings, too
    Well, Warmoth currently drills for Schaller BMLs which are 17.5mm. It's gotta be 16mm, based on Ham's suggestion.
  6. Um, 16mm is .63" so go for the 5/8" at .625" forstner and you should be fine.

    Since the 17mm is too large at .669 and the 11/16" is even larger at .6875" the only thing left is the 5/8" or a 16mm if you've only got metric.
  7. StuartV

    StuartV Finally figuring out what I really like Supporting Member

    Jul 27, 2006
    Manassas, VA
    Apologies for dredging this up from the past, but I have pretty much the exact same problem as the OP.

    I'm trying to fit Hipshot Ultra-lites in an Allparts Jazz neck.

    The holes that are there, from the factory, are not the same diameter all the way through. The bigger part goes most of the way through and, after measuring, I concluded as 11/16". The smaller part, at the bottom, seems to be 9/16".

    The bushings for the Hipshots fits in the bigger part with just a little bit of play, but doesn't fit through the narrower bottom part.

    So, I ordered up an 11/16" Forstner bit to ream the bottom of the hole out to match the top. Unfortunately, the bit does not fit inside the bigger part of the hole. So, I went and bought a 5/8" Forstner bit and drilled a test hole in a piece of scrap maple. That hole is too small and the bushing won't fit in it. I went ahead and bored a test hole in the scrap using the 11/16" bit and the bushing fits in it, but it's too loose for my taste.

    So, like the OP, I believe a 21/32" Forstner bit should be just right. Or, by my calculations, 21/32" works out to 16.7mm, so maybe a 17mm bit would work.

    The problem is, I can find a 19/32" Forstner bit and sizes bigger than 11/16". But, no 21/32" anywhere.

    All this begs the question, what are other people using to install Hipshot Ultra-lites? Can anybody tell me where to get a 21/32" Forstner bit?

    Are y'all installing these in a true 11/16" bore and just not worrying about the extra play around the bushing?

    I think I saw either 16mm or 17mm or both. Would one of those work?

    Thanks for any help!
  8. grisezd


    Oct 14, 2009
    A dowel with a wrap of sandpaper spun in a drill (or Amish, by hand) should get you there.
  9. Musiclogic

    Musiclogic Commercial User

    Aug 6, 2005
    Southwest Michigan
    Owner/Builder: HJC Customs USA, The Cool Lute, C G O
    17mm is the bit you want for the Allparts neck, just checked an Allparts vintage jazz I have in stock. 17mm fits perfectly...Japan...go figure, LOL it's metric. If only they used SAE...LOL. Good luck with it
  10. StuartV

    StuartV Finally figuring out what I really like Supporting Member

    Jul 27, 2006
    Manassas, VA