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shaping a new bridge

Discussion in 'Setup & Repair [DB]' started by swamprocker, Dec 21, 2011.


  1. question i didn't find and answer to under search...

    if I am shaping a new bridge, and if it is adjustable, can i use the feet off the old bridge? then only have to size the top?
     
  2. 360guy

    360guy Supporting Member

    Apr 28, 2006
    Lansing, MI USA
    Is there a reason you're not using the upper part of the existing bridge?
     
  3. the upper part is warping.
     
  4. Hi.

    Yes, theoretically, but unless both the new and the old bridge are exactly the same, You still have to shape the feet as well.
    It's not likely that the feet will flex the same either.

    The spreader is easy enough to make if that's what worries You.

    I have only experience about a few bridge shapings, but the feet were the best part IMHO. Perhaps the sense of accomplishment or something like that ;).

    Regards
    Sam
     
  5. great point. thanks.
     
  6. 360guy

    360guy Supporting Member

    Apr 28, 2006
    Lansing, MI USA
    Try this: put the warped, old bridge upper part into some boiling water for about 15-20 minutes. It will straighten back. Let it dry 24 hrs. It should be good to go. At the very least you' ll have a back up bridge.
     
  7. Thanks!! i will give that a try. the bridge i tried to order is out of stock and i need to have a fix by new years. \m/

    after i boil it, should i clamp it between some straight wood??
     
  8. bssist

    bssist

    Jun 23, 2007
    St. Louis, MO USA
    What is the "secret" to shaping bridge feet? I tried a few years back by placing sand paper on the top and rubbing the bridge against it (before installing adjusters) but the result was less than optimum. I ended up letting a pro properly shape it for me.
     
  9. i'm guessing LOTS of patience and lots of sandpaper of different grit
     
  10. I put mine between two cinderblocks, put 100 pounds on top of it, and left it alone for a week.
     
  11. Cody Sisk

    Cody Sisk

    Jan 26, 2009
    Lilburn, GA
    Ronald Sachs Violins
    While this is a good temporary fix, it will soften the maple and the warping will come back quicker the second time around. You still need to be ready to replace it.
     
  12. Eric Hochberg

    Eric Hochberg Supporting Member

    Jul 7, 2004
    Chicago
    My student's straightened out warped bridge warped again after 3 months.
     
  13. thanks...this is only going to be a temp fix...i have a new bridge ordered. however, i will not get it in time to shape before New Years Gig.
    and i have too many gigs already set in 2012, NOT to put on a correct fix asap

    i appreciate everyone's input.
     
  14. JoeyNaeger

    JoeyNaeger Guest Commercial User

    Jun 24, 2005
    Houston, TX
    Bass Specialist, Lisle Violin Shop
    Sandpaper fitting is generally considered a poor method. Pros use some kind of crayon or something to mark the top. Then you carefully shave the feet where the crayon transfers. Start with a knife or a chisel and move to a scraper as the fit gets closer.
     
  15. Hi.

    There's really no secret, just a tool.

    Called a leg spreader :D. ( aren't all DB's just that)

    Since I'm not a luthier, mine is just a long M6 (1/4) nut with carriage bolts on both ends. One nut and 2 sets of bolts are enough to cover the entire range from 1/8 to 5/4 bass bridges.

    A rigging screw type would be much better, obviously, just haven't gotten around to make one. Yet ;).

    The method I use, is that I rough shape the feet without the spreader, string the bass up to tune, install the spreader so it is snug, and shape the feet to match the contours of the top.

    If the feet flex a lot, or if the top is very soft, it's a good precaution to place thin, flat strips of wood between the top and the pre-shaped legs when stringing up to tune. Otherwise the inside edges of the feet may dig into the top. NOT RECOMMENDED.

    BUT, I feel the need to stress this once again: I AM NOT a luthier, just a DIYholic with very inexpensive basses, so do take my advice keeping that in mind.

    Regards
    Sam
     
  16. iiipopes

    iiipopes Supporting Member

    May 4, 2009
    Shaping the feet to the top: doesn't anybody lightly tape sandpaper, grit up, to the top with something like painter's low-tack masking tape (so it won't do anything to the finish), and then rub the bridge feet fore and aft (fingerboard to bridge, about an inch each way from the f-hole notches - NOT across soundhole to soundhole) to conform the feet to the top?
     
  17. JoeyNaeger

    JoeyNaeger Guest Commercial User

    Jun 24, 2005
    Houston, TX
    Bass Specialist, Lisle Violin Shop
    Some shops do, but this results in the feet becoming slightly rounded. It will look like a perfect fit, but you will be able to rock the bridge back and forth slightly with the strings off. A sign of a really well fitted bridge is one that does not rock at all.
     
  18. bssist

    bssist

    Jun 23, 2007
    St. Louis, MO USA
    Thanks for all the information. I understand the carving info but I think I've missed something on the leg spreader (do you feel a draft, who left the door open?:D).
     
  19. 1st Bass

    1st Bass

    May 26, 2005
    Forest Grove, OR
    The compression stress on the top of the bridge results in the feet spreading apart a little bit (~ 3mm?). If you fit the feet without taking that into consideration, the feet will not feet once the strings are under tension. So we use a tool called a bridge leg spreader that pre-stresses the bridge to approximate the position they will take under load. Then we fit the feet.

    You can either buy them or make them. I made mine out of a small turnbuckle, so that I could simply twist the middle, and both ends would move in or out.

    Does that help?
     
  20. Hi.

    Yep, as the "rough" mating, before and after using the spreader.

    But, after that it's very easy and quick job to carve the feet to match the top exactly. That takes only a few minutes IMLE, so why on earth would anybody skip that important part of the mating?

    Regards
    Sam
     

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