Boring out holes for larger tuning heads

Discussion in 'Luthier's Corner' started by D.A.R.K., Jul 19, 2018.

  1. Nohrellas


    May 11, 2016
    I've done it successfully with a standard drill bit of the correct size. I didn't use a wood bit, as weird as that sounds, but rather a metal bit since those center properly in the large hole and just drill out the remaining material on the side. Not a perfectly clean job but it works without any special tools.
  2. Bruce Johnson

    Bruce Johnson Commercial User

    Feb 4, 2011
    Fillmore, CA
    Professional Luthier
    So you understand, I have a machine shop and I specialize in making custom tools for Luthiers. I make up all kinds of custom reamers, counterbores and specialty cutters, including the special taper reamers for violin/cello pegs.

    What Stew-Mac (who are friends of mine, BTW) is showing in that video is how to use a fairly expensive tapered peg reamer to enlarge the size of a straight hole. Okay. Not very efficient, but it will work if you already have one of those tapered reamers. I certainly wouldn't buy a tapered peg reamer just to do straight holes in an electric bass.

    Why not just use a straight unpiloted 9/16" Chucking Reamer? You can get one on Amazon for about $15. It will make a nice smooth precise 9/16" hole every time. You can use it in a drill press or turn it in gently by hand, if you like.

    A reamer with a pilot on the front, like the one I showed above, is better because it guarantees that the enlarged hole stays centered on the original hole. That style of reamer, even made to custom dimensions, isn't very expensive; like $25-$40. It can be used in a drill press or turned in by hand.

    A key thing about a straight reamer, like the one I showed above, is that it primarily cuts on the front edge of the teeth, so there's hardly any force pushing outward that could potentially split the headstock. Forstner bits and brad-point bits also do not push outward. That's why you want to use them for drilling headstocks.

    Taper reamers and standard point twist drill bits do push outward with quite a bit of force. That's why you want to be careful with them on fragile wood parts. Particularly those commercial tapered T-handle reamers. Because of the shallow angle, they can exert a lot of force trying to split the wood apart. If you use one of those, go slowly and gently.

    To repeat what I said in my first post above, the best way to do this job is with a piloted straight reamer. It's the right tool for the job. But, I can assume that most of you who just want to fit a set of tuners on your own bass, don't want to spend the money on a special tool for one use. That's why I recommended enlarging the holes by hand with a round file, or plugging the holes and redrilling them with a Forstner bit. From my experience, those are the two best low-risk techniques. Pretty hard to screw up. There's other techniques, which you guys have used successfully. But each has their own extra risks.
  3. FenderB


    Mar 28, 2016
    Findlay, Ohio
    Agree with navijaz, buy a reamer. It will give you the best results and the peace of mind that you did it the right way.
  4. cavemanbass


    Nov 5, 2010
    I used my handy Dremel tool for this. On that particular headstock I did not want the new holes centered so as to keep the spacing between tuners right. I drew the outline of the enlarged hole on both sides of the headstock and very carefully sanded with a tiny drum sanding bit. Worked out well. However if I wanted to keep the holes centered I think @Bruce Johnson has described a great way to go. I didn't know that type of bit even existed so thanks for the info!
  5. BobKos

    BobKos Supporting Member

    Apr 13, 2007
    If you're careful & patient, use a 1/2" sanding drum on a dremel (included with most dremel kits). As suggested above, draw guide circles on both sides so you cut enough without over-doing. Work slowly. It will turn out fine.
  6. fhm555

    fhm555 So FOS my eyes are brown Supporting Member

    Feb 16, 2011
    Reamers are cool and if you have some experience with them they will get the job done, but if you don’t own one and don’t have any experience using one, the plug and redrill method Bruce described would be the way i’d go. To avoid chipping get a new, quality fostner bit and as instructed, drill from both sides and meet in the middle.
    That said, if you can get a tech to do it for half the cost of a reamer, that would be the way to go.
    I replaced some machine heads on my brothers old Silvertone guitar with a set from a strat and i just took a hand drill and worked slowly to enlarge the holes and it went fine, but it was a particle board headstock so it was much easier to drill.
    D.A.R.K. likes this.
  7. D.A.R.K.


    Aug 20, 2003
    This is great, it's awesome to get so much info from people who are pro's as well as those who have experienced DIY. I really appreciate everyone's input very much!!
  8. ficelles


    Feb 28, 2010
    Devon, England
    Yes that type, nothing wrong with the reamer itself though, I think the problem was with the user (i.e. me!)... the advice others have given of going slowly and a little bit from each side of the hole is the way to do it, I think I went too hard at it and the very sharp reamer blades cut into the wood too deep, resulting in holes much less than perfectly round.
    D.A.R.K. likes this.
  9. I use countersink bits to widen tuner holes.
    Just to demonstrate I used a 16mm bit on a 12mm hole (had these sizes just laying around)


    Halfway through

    Finished from the other side

    It is pretty much centered and perfectly round
    D.A.R.K. likes this.
  10. Paulabass


    Sep 18, 2017
    There's more than one way to skin a cat. One thing is for certain. DO NOT just try to ram a twist drill thru. If you don't split the headstock, your hole will be way off center.
    bolophonic and Gilmourisgod like this.
  11. Bruce Johnson

    Bruce Johnson Commercial User

    Feb 4, 2011
    Fillmore, CA
    Professional Luthier
    Yes, there are many ways to do this hole enlargement thing, with varying amounts of risk involved. Using a countersink or a step drill to establish the new hole size on both sides is okay. Just be careful, because either one will try to peel up a spiral from the surface. Once you have the circles described on both sides, the safest thing is to then use a round file to bring the inside of the hole out to the diameter of the circles.

    Jamming a big drill bit down in there has a big risk of splitting. It can be done, but you have to be very careful not to let the bit dig in. The safest big drill bits are Forstner bits or Brad Point bits. But if you have one of those, I still recommend the plug and tiny pilot hole method. That's the safest all around.
    JIO and D.A.R.K. like this.
  12. Camaro


    Sep 25, 2013
    Germany, NRW
    Don't fear the reamer ...
  13. While on the subject of Dremel Tools, they are GREAT if one has very steady hands...
    but those who do not have steady hands have made me a small fortune over the years doing repairs ;)

    The little Dremel Drill about as wobbly as you can imagine. It helps a LITTLE,
    but it really just doesn't have the mass to be truly steady for perfect holes...
    it is, on the other hand, the perfect thing to use as a Desktop Sander Mount for when you need
    to have a third hand...slap the Dremel in the Press, and use both hands to work the wood/etc
    as you need to.
  14. Primary

    Primary TB Assistant

    Here are some related products that TB members are talking about. Clicking on a product will take you to TB’s partner, Primary, where you can find links to TB discussions about these products.

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