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Methods to increase tuner bore holes in headstock

Discussion in 'Hardware, Setup & Repair [BG]' started by Tom0Blam0, Aug 31, 2017.

  1. Tom0Blam0

    Tom0Blam0 Supporting Member

    Mar 16, 2014
    I have a bass with irregularly sized bore holes. I also have some tuning machines that fit 11/16" bore holes. So my plan is to enlarge the existing holes, but I want to make sure it goes as smoothly as possible. I have a drill press, but I want to make sure I use an effective process. I was thinking of using a step bit to increase the size to 11/16" from the back of the headstock and then increase the entire size of the hole to 11/16" with an 11/16" spade bit.

    My question is, will this strategy work? Is this the most effective method of going about increasing the size? Alternative strategies that would work better/be safer. I want to avoid damaging the neck as much as possible.

    Any advice is much appreciated.
  2. Turnaround

    Turnaround Commercial User

    May 6, 2004
    Toronto Canada
    Independent Instrument Technician, and Contractor to Club Bass and Guitar - Toronto
    Other than the spade bit it sounds like a good approach. I would use the step bit to enlarge the hole from both sides of the headstock, then finish it with a spur bit. Regular twist drill would also work rather than the spur bit. I generally avoid spade bits wherever possible - they are a pretty crude device.
    Spidey2112, RSBBass and Picton like this.
  3. Bruce Johnson

    Bruce Johnson Commercial User

    Feb 4, 2011
    Fillmore, CA
    Professional Luthier
    The neatest and safest way to enlarge tuner holes like that is with a router and a small (like 3/8" dia) top-bearing bit. Take a piece of MDF or hardwood, and make a neat 11/16" hole in it with your spade bit or whatever you have. Tape and/or clamp that onto your headstock, lining it up over the old hole just as you want it. Use the router, gently, to enlarge the hole, working the depth down in 1/8" steps.

    The faster alternative is a special counterbore bit. I have ones that I've machined up myself, and supplied to other Luthiers. But you probably don't need to go there for a one-off repair like this.
  4. geddeeee


    Jun 30, 2006
    Or.. Just use a tapered reamer.

    Used it on my Rickenbacker bass to fit some Grover Titans. I'm no expert by any means, but it worked perfectly!!!
    RSBBass, mongo2 and Picton like this.
  5. Tom0Blam0

    Tom0Blam0 Supporting Member

    Mar 16, 2014
    Thanks all. I will probably go with Bruce's suggestion as I want to avoid damaging the headstock as much as I can.
  6. Arie X

    Arie X

    Oct 19, 2015
    well, whatever you do clamp it down and take your time. you certainly don't want to hand hold this.
  7. Picton


    Aug 16, 2017
    Reading, MA

    And yes, a spade bit is not going to yield the best results IMO.
  8. saltydude


    Aug 15, 2011
    boston CANADA
    Being a machinist I'd use my trades approach. Definitely secure the headstock as best as possible, angularity and all. Indicate each hole individually with a dial indicator and REAM or possibly endmill each one. Might be time consuming but I'd be confident it was done properly.
    rllefebv likes this.
  9. Arie X

    Arie X

    Oct 19, 2015
    certainly my preferred choice (i own a mill) but not everybody has access to one. :) tool and die work ruined my life -now i can't even whittle a stick without some level of precision over-kill involved. i have a severe quality problem.
    rllefebv likes this.
  10. tlc1976


    Aug 2, 2016
    If you decide to drill thru, I would clamp a scrap piece of wood over the exit side of the hole, and let the drill go into the scrap wood. Otherwise the headstock wood can tear out. Even better, predrill the new hole thru another piece of scrap and clamp that on the entry side as well, using it as a guide.

    What I know as a spade bit won't work unless the hole hasn't been drilled already, but a small pilot hole might be ok.
  11. mongo2


    Feb 17, 2008
    Da Shaw
    Yep, tapered reamer.
  12. Bruce Johnson

    Bruce Johnson Commercial User

    Feb 4, 2011
    Fillmore, CA
    Professional Luthier
    The problem with a tapered reamer is that it makes a tapered hole. The bushing is designed to go into a straight hole. In a tapered hole, the bushing will be too loose at the top and too tight at the bottom.

    You can use a tapered reamer to bring the top edge of the hole to 11/16", then use that to guide-start a straight 11/16" drill bit, turning it gently by hand. Riskier than the other methods we've talked about, but it will work.
    Last edited: Sep 3, 2017
  13. Jeff Scott

    Jeff Scott Rickenbacker guru.......... Supporting Member

    Apr 11, 2006
    How about a Forstner bit? I've used them for similar projects with excellent results.
  14. Bruce Johnson

    Bruce Johnson Commercial User

    Feb 4, 2011
    Fillmore, CA
    Professional Luthier
    If you try to use a Forstner bit to enlarge an existing hole, it will jump and kick and chatter as it tries to get started. Just like a brad point, it needs to locate its point in something solid.

    But there are two ways that you can use a Forstner bit to enlarge a tuner hole:

    One way is to plug the hole first. Make up a wood plug from a piece of dowel or scrap wood and lightly glue it in place. Locate the center carefully and drill a little hole, like 3/32" down through it. Now you can drill the hole out with the Forstner bit (or a brad point bit). The point of the Forstner bit will follow the little hole.

    The other way is to pilot on the OD of the Forstner bit. If you have an 11/16" Forstner bit, use it to drill a hole in a piece of 3/4" MDF. Then clamp that piece of MDF tightly down onto the headstock, lining it up over the existing hole. With the drill press shut off, lower the Forstner bit down partway into the hole in the MDF. Holding it in there, start the drill press and start drilling.
    Coolhandjjl likes this.
  15. I've never done this on a bass but to enlarge 1/4" guitar tuner holes to 10mm I have a 1/2" reamer that I ground off at approximately the 10mm point so I run that through the existing hole then clean up (carefully) with a 10mm drill bit. You might have to look a little to find a reamer big enough for bass tuners. A machine shop could do the grinding. Don't know if the cost is worth it for a one time job, however.
  16. Bruce Johnson

    Bruce Johnson Commercial User

    Feb 4, 2011
    Fillmore, CA
    Professional Luthier
    Well yeah, the neatest, fastest way to enlarge a tuner hole from one size to another is with a custom pilot reamer. Like this:

    IMG_1826B.jpg IMG_1827B.jpg

    That's exactly what this is: A custom made reamer which fits in one size hole and enlarges it to another size. A couple of seconds in a drill press. I make them up from tool steel or stainless steel. With a lathe, a mill and a spin index fixture, they are really quite simple to make. I have maybe 30 of them I've made up in various sizes for different jobs. This one is actually for tuner post bushings. I've made custom reamers like this for many pro Luthiers.
  17. Turock


    Apr 30, 2000
    Wrap some sandpaper around an object like a pencil.
  18. Coolhandjjl


    Oct 13, 2010
    Do the tuners use a ferrule? If so, you could have those turned to the size you need and won't have to touch your bass.
  19. Jeff Scott

    Jeff Scott Rickenbacker guru.......... Supporting Member

    Apr 11, 2006
    I did so with excellent results by using a drill press and clamping the bass solidly to the table.

  20. Yes sir. And if I was in "official" business I'd be asking how big of a check you want for a couple.:thumbsup:

    For now, I'm muddling through with what I have.

    Always a joy to see your work though.

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