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Thread: Bridge setup feasibility

  1. #1
    Mindin' my own bizness BJ O'Day's Avatar
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    Default Bridge setup feasibility

    Hi,

    I'm following Robert Meldrum's guide to set up a cheap mandolin I use when traveling. It is an arch top made from formed plywood. I removed the bridge to get a better fit against the sound board. The top is indented from the old position. The old position is wrong. The correct position will have the bridge resting halfway on the normal section and half resting on the indented section.
    Outside of sculpting this to fit is there a way to make this work?
    I'm not trying to make a masterpiece. I'm just trying to make some improvements.
    Any ideas or comments are appreciated.

    Thanks
    BJ

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    I may be old but I'm ugly billhay4's Avatar
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    Default Re: Bridge setup feasibility

    This is a tricky problem, hard to fix without damaging the finish. You've got two places to work --- the bridge bottom and the top top (if that makes sense). The bridge bottom will present fewer refinishing issues, but will be hard to make right.
    I think I might glue a small shim on the bottom of the bridge where it will have to sit on the indent and shape the shim, not the bridge itself. Won't be easy, though, but at least it's reversible if the shaping goes wrong.
    To do this shaping, coat the bottom of the bridge with chalk and press onto the top and wiggle a bit. Where the chalk has work off is where the bridge is touching and needs material removed. Do a bit and rechalk and do it again. When all the chalk wears off, you have a perfect fit. For removing material, a very sharp knife, a small file, and perhaps even a small piece of sandpaper will do.
    That's the best I can come up with.
    Bill
    IM(NS)HO

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    Default Re: Bridge setup feasibility

    I have never heard of a problem like this, but if the indent isn't too awfully deep you could try filling it with something to level it off. Maybe clear nail polish for instance, or shellac that has been set out and allowed to thicken a bit, or even high viscosity superglue. In other words, the same techniques that would be used to fill a dent on an instrument if the dent were anywhere else. There are several good articles on dent filling in the Stew Mac Trade Secrets archive. But think about this. If the old bridge made an indent in its old position, don't you think it's fairly likely that it will create an indent in its new position. If it does, then what?
    Don

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    Registered User DavidKOS's Avatar
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    Default Re: Bridge setup feasibility

    It's time- consuming, but you could fit the bridge like a violin bridge is fitted, using sheets of sandpaper:

    http://www.violinresearch.com/violin_032.htm

    http://www.maestronet.com/forum/inde...ing+%2Bcarving



    http://fiddlerman.com/2011/11/instal...kevin-m-healy/

    It depends on how deep the indents are on the laminated mandolin.

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    Default Re: Bridge setup feasibility

    Conservative thinking: assess how stable the top is if you move the bridge and use light gauge strings (or even just 4 strings), will it increase the crater, and can you get a bridge with bigger feet?

    Radical: a violin soundpost.
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    Default Re: Bridge setup feasibility

    Quote Originally Posted by DavidKOS View Post
    It's time- consuming, but you could fit the bridge like a violin bridge is fitted, using sheets of sandpaper
    I haven't checked your links, but I would have to disagree that that is how a violin bridge "IS " fitted ... it can be fitted like that, after a fashion, but in the world of top-grade luthiers, violin bridge feet are only ever fitted using a sharp knife and a marking medium ... like chalk or carbon paper.
    Last edited by murrmac; Jan-07-2016 at 5:52pm.

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    I may be old but I'm ugly billhay4's Avatar
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    Default Re: Bridge setup feasibility

    I, too, thought of filling the indentation but couldn't think of a way to do it without it showing badly. As for David's suggestion, this is done with bridges, but in this case, because the mating surface on the top is irregular, would not work very well. This is why I suggested the more traditional chalk and knife technique where you can get a pretty exact fit.
    Bill
    IM(NS)HO

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    Default Re: Bridge setup feasibility

    How deep is the indentation? If it is mostly in the finish I would remove the finish so the bridge could be fit properly. A lot of mandolins have marks from where the bridge sat in the wrong place. This is not a collector instrument so I would worry more about sound than looks. Something I usually do anyway. It's all about the sound.
    THE WORLD IS A BETTER PLACE JUST FOR YOUR SMILE!

  11. #9
    Certified! Bernie Daniel's Avatar
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    Default Re: Bridge setup feasibility

    Quote Originally Posted by multidon View Post
    I have never heard of a problem like this, but if the indent isn't too awfully deep you could try filling it with something to level it off. Maybe clear nail polish for instance, or shellac that has been set out and allowed to thicken a bit, or even high viscosity superglue. In other words, the same techniques that would be used to fill a dent on an instrument if the dent were anywhere else. There are several good articles on dent filling in the Stew Mac Trade Secrets archive. But think about this. If the old bridge made an indent in its old position, don't you think it's fairly likely that it will create an indent in its new position. If it does, then what?
    Never encountered this kind of thing either but I like the idea of filling the depression with shellac or lacquer.

    The idea of letting it sit on the bench to thicken (evaporate the solvent) to honey viscosity is great. I've done this trick before to fill in on some inlay and it works just great. You'll need to give it plenty of time to fully harden.

    If you want to get fancy you could add some dye to the shellac that would match the top board wood so the fill would be much less obvious.

    If you go with fitting a small appendage on the base of the bridge you will have essentially anchored bridge in place and you could not slide it back and forth (intonation), or side to side (string centering) on the fret board some time down the road?
    Bernie
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    Mindin' my own bizness BJ O'Day's Avatar
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    Default Re: Bridge setup feasibility

    Thanks for the replies and suggestions. I placed paper on the arch and was sanding to match. I was adjusting the intonation when I found the old position was wrong. The indent is deeper than the finish, (>1mm).

    I have also sanded as far as I can go on the bridge. The screws are starting to appear on the bottom. So I'll either spring for a new bridge and start again, or maybe glue a thin strip of walnut to the bottom of the bridge and try the chalk method.

    It's all a learning process. There is no pressure when starting with cheap mando that I can only make better.

    BJ

  13. #11

    Default Re: Bridge setup feasibility

    Wax paper on the top of the mandolin. Epoxy on the bottom of the bridge. String it up (at least the g and e strings). Let it cure in place. Trim up the epoxy where it oozed out.
    Not a fix on a "good" instrument but it should do on a plywood beater.
    Bill Snyder

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    Registered User bernabe's Avatar
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    Default Re: Bridge setup feasibility

    A picture would be helpful, but if the indentation doesn't span the entire length of the bridge footprint [i.e indents only from the inner or outer edge of the bridge feet from improper fitting], move it to the correct position and fit as best you can and pressure may settle things in or force the top back to its proper profile by applying even pressure from the proper fit. Without seeing it is hard to picture what this indentation is or how big it is.

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    Registered User DavidKOS's Avatar
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    Default Re: Bridge setup feasibility

    Quote Originally Posted by murrmac View Post
    I haven't checked your links, but I would have to disagree that that is how a violin bridge "IS " fitted ... it can be fitted like that, after a fashion, but in the world of top-grade luthiers, violin bridge feet are only ever fitted using a sharp knife and a marking medium ... like chalk or carbon paper.
    I know, but the sanding method could work in this case. Plus, I'm not a top-grade luthier! I'm just an instrument tech.

    Quote Originally Posted by billhay4 View Post
    I, too, thought of filling the indentation but couldn't think of a way to do it without it showing badly. As for David's suggestion, this is done with bridges, but in this case, because the mating surface on the top is irregular, would not work very well. This is why I suggested the more traditional chalk and knife technique where you can get a pretty exact fit.
    Bill
    It was worth suggesting, sorry it can't help.

  17. #14

    Default Re: Bridge setup feasibility

    Wax paper on the top of the mandolin. Epoxy on the bottom of the bridge. String it up (at least the g and e strings). Let it cure in place. Trim up the epoxy where it oozed out.
    Not a fix on a "good" instrument but it should do on a plywood beater.
    THIS is the solution. And it's totally reversible later by changing the bridge or re-fitting the bottom of this bridge. The only other method is to "chalk fit" the bridge to the top (as has been described), but that's a lot of work and takes some real skill to get a good fit. Anything you do to fill the dent in the top is going to look bad.

    Steve

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    I may be old but I'm ugly billhay4's Avatar
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    Default Re: Bridge setup feasibility

    I believe this is a better solution than those I suggested.
    Bill
    IM(NS)HO

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    Mindin' my own bizness BJ O'Day's Avatar
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    Default Re: Bridge setup feasibility

    Thanks,
    I think I'll give the epoxy a try.
    BJ

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    Registered User DavidKOS's Avatar
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    Default Re: Bridge setup feasibility

    Quote Originally Posted by Bill Snyder View Post
    Wax paper on the top of the mandolin. Epoxy on the bottom of the bridge. String it up (at least the g and e strings). Let it cure in place. Trim up the epoxy where it oozed out.
    Not a fix on a "good" instrument but it should do on a plywood beater.
    This may work.

  22. #18
    I may be old but I'm ugly billhay4's Avatar
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    Default Re: Bridge setup feasibility

    I do believe you'll need a very viscous epoxy mix for this. And clean off the bottom of the bridge with acetone before expxying. This will help it stick better. Roughing it up won't hurt either.
    Good luck.
    Bill
    IM(NS)HO

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    Default Re: Bridge setup feasibility

    The one downside I can see to the epoxy on the bridge itself is that, once the bridge foot has been molded to match the indentation, it will have to stay there and you won't be able to re adjust the intonation in the future.

    It is possible to fill a dent on an instrument and not have it look bad. Tinting whatever you use to match, scraping down with a scotch taped razor blade, sanding with narrow strips of sandpaper and very light finger pressure, and hand buffing to blend in. That way you could adjust intonation in the future.

    That being said, I agree that the epoxy on bridge foot technique is quicker, easier, and probably good enough. As long as nothing else changes with the wood.
    Don

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    Default Re: Bridge setup feasibility

    If there is a future change you can:
    a. get a new bridge
    b. sand the epoxy
    Bill Snyder

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    Default Re: Bridge setup feasibility

    c. get new beater

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