Sanding Down the Bridge

Discussion in 'Setup & Repair [DB]' started by Tchar, Sep 27, 2016.


  1. Tchar

    Tchar

    May 8, 2016
    Québec
    Hi,

    I've been thinking of sanding down the bridge on my bass. The action is quite high, and the adjustment wheels (I don't know if they have a name) are all the way in. The only option I see to lower the action would be to sand it down and remove a bit of wood.

    Does anyone have any experience with this kind of thing? I've never tried something like it, would I be better off just bringing it to a luthier's?

    Thanks a lot!
     
    Don Kasper likes this.
  2. Are you a gambling man? Where I live a new bridge is $300 US. What are the string heights now?

    Many times I've successfully lowered string height by filing down the string slots and shaping the crown with a belt sander, but you have to be on your toes and know what you're doing.
     
  3. Don Kasper

    Don Kasper Supporting Member

    I've done this before - clamp your belt sander (see below) on it's side on a flat surface so that it can't move, but can operate. Then, while the bridge is still ON the bass, calculate and mark the bridge (in pencil) for:
    1. string spacing along the curvature - center-to-center.
    2. if maintaining the same "relative" curvature of the bridge, calculate how much you're going to remove. You need to do the math if you're going to change the "relative" height of the strings. Capish?
    Draw a line in an arc, for the desired final height.
    Now remove the bridge (remove the adjusters and feet - mark them G/E!), and lay the bridge flat so that you can gently press it into the belt sander, removing just a little bit of the arc with each pass, until you reach the pencil line. Slow and steady wins the race. (Note: I like using a small piece of painter's blue tape to mark the exact location of one of the bridge feet on the top of the bass - You want to be able to replace the bridge to the Exact spot where it was prior to its removal. It's a game of mm.
    Now, you'll need the exact file sizes to cut the grooves for the strings - NOT TOO DEEP! (I believe no more than "1/3 of the diameter of the string" is acceptable.) I also have used old Roundwound BG strings of the appropriate diameter to gently cut the groove to the desired width, after making a thin groove for the desired depth.
    You should also clean up the completed arc using a file or sandpaper to break any sharp edges and make it look Professional-like.
    Not EZ, but not Impozzible.
    IMO.
    Good Luck.
    (Did I mention I'm not a Luthier?)
    Makita-9924DB-3-X-24-Belt-Sander.jpg
     
    Last edited: Sep 28, 2016
    dderatz likes this.
  4. I did this with two of my bridges.

    I changed the curvature a bit too much to get the largest bowing angle for my five string instrument. No problem with adjusters to correct that, but less nice with the solid bridge. Anyway they are playable, just could have been a bit better.
    So be careful if you want to change the curvature of the bridge.

    For the string slots: mark the position with a pencil by a line going down in parallel to the ribs (NOT perpendicular to the tangent of the bridge slot!).

    It would be less dangerous if you lower the bridge height for all strings the same amount, so the bowing angles are the same (even for the outer strings). If you lower them fractionally (i.e. 100% for G, 67% for D, 33% for A and 0% for E), you get a smaller bowing angle for the G. Might be no problem on a 4-string.

    Don't go too low in the first place. Go down by 1 mm increments and try the new action height before you go lower. If you get buzzing at some positions, you need the fingerboard to be planed. OK, you have adjusters, so you might compensate with them, but even in this case I wouldn't go down more that two millimeters first.

    Don't forget to round the bridge slots towards tailpiece and fingerboard so that there are no edges that can cut into the string.

    On the E string you might need to make the slot a bit deeper than 1/3, at least on the inside. The force goes parallel to the ribs, so needs the slot itself. 1/3 string diameter is fine for the outside edge of the E slot.

    Personally I would't go lower than 6 mm on the G without adjusters and no lower than 5 mm on the G with adjusters.

    Good luck!
     
  5. Ortsom

    Ortsom Inactive

    Mar 23, 2016
    Ample advice to cover most issues, only thing I might add is: when you measure the string heights, make sure not only the bridge feet are positioned correctly (between the nicks, as well as laterally centred; masking tape?), but also that the bridge is oriented correctly (so TP-side of the bridge is perpendicular to the top: mid-line bridge bisects string break angle). Use a plastic square for that (or maybe a book or a DVD cover). Know the proper scale, in this position & orientation. Measure string heights tuned & verify consistent bowing clearance.

    Consider first filing grooves to get the strings to the desired place, and when that's done finish the crest as desired. The grooves should have a slightly wider diameter than the strings, and be well rounded to fit the string break angle. To reduce friction, apply pencil lead to finish them off (also in the nut, while you're at it).

    Bonne chance!
     
    DoubleMIDI likes this.
  6. jmpiwonka

    jmpiwonka

    Jun 11, 2002
    i had to do this on a beat up old bass i got a while back. strings were way high, but it was fine because i could fine tune to my preference. I went the slow way!! i used some larger nicholson files i have to thin it all out, i don't own a belt sander.
    for the string slots i have some nut files so i just used those...

    just remember, it's easier to remove material than it is to add it...
     
    Povl Carstensen likes this.
  7. RSBBass

    RSBBass

    Jun 11, 2011
    NYC
    Has it always been this way? If not I would be inclined to have a pro look at it to see that you don't have a more serious problem.
     
    Steven Ayres and DoubleMIDI like this.
  8. powerbass

    powerbass

    Nov 2, 2006
    western MA
    Belt sanders are the quickest way to ruin wood! Seriously, step away from the belt sander. I'm no luthier so.... you can remove wood from the post that attaches to the feet or you can remove wood from the top part. If you remove too much wood from the top you get too close to the little heart shaped hole. A competent luthier will look at the whole bass and just what is the best way to address your bridge.
     
  9. 1st Bass

    1st Bass

    May 26, 2005
    Forest Grove, OR
    Something I do on all instruments, not just basses:

    When lowering string clearance, I loosen one string at a time, enough to slide it off the bridge and out of the way. Then I use a round file to deepen the string-groove until that string is at the right height. I can get an estimate with the string in place, by pushing the string down with my finger just above the bridge, until it is at the right height above the fingerboard, but I check often, to make sure I don't go too deep on any string groove.

    Then, when all four strings are at appropriate heights above the fingerboard, I remove the bridge entirely and use a small, very sharp plane (or, in some cases, a knife) to reduce the top of the bridge to the appropriate curve, then use flies to adjust the thickness and to make it glassy smooth, before re-installing the bridge on the instrument.

    No belt-sander, there...sorry. It is so easy to do it with hand-tools, at near-zero risk, that I can't see playing with such an aggressive tool. I have noticed, that nowadays they sell chainsaw-sharpening files in a very wide range of diameters. The ones I have tried (at appropriate diameters) work very well as bridge and nut files, for very reasonable cost.

    Do remember to round the sharp edges of the string grooves, and to lubricate with graphite (pencil-lead) before re-installation.
     
    Povl Carstensen likes this.
  10. I may be missing something, but... If the bridge is equipped with height adjusters, why not just take a few mm off of the bridge legs instead of messing with the topside arc?
     
    Matthew Tucker, Ortsom and robobass like this.
  11. Greg Clinkingbeard

    Greg Clinkingbeard Commercial User

    Apr 4, 2005
    Kansas City area
    Black Dog Bass Works
    I've been waiting for someone to say this. If the arch and string spacing is right, I'll do this.
    It's important to maintain the proportions.
     
    Last edited: Sep 30, 2016
  12. robobass

    robobass

    Aug 1, 2005
    Cologne, Germany
    Private Inventor - Bass Capos
    Yes. If you have access to a good table saw, Mount the bridge to a board with screws or double sided tape, and you can remove a small slice from the legs very cleanly. If the holes are deep enough, then you can put the adjusters right back in and set up the bass in about 2% of the time and trouble of cutting the top of the bridge.
     
    Last edited: Oct 2, 2016
  13. neilG

    neilG

    Jun 15, 2003
    Ventura, CA
    A disc sander works really well for shortening the bridge. Takes a minute. Getting a good square marking across both feet is the trick.
     
  14. Primary

    Primary TB Assistant

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