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Thread: Custom compensated bridge?

  1. #1

    Default Custom compensated bridge?

    So one of my mandolins is tuned to a non-standard tuning (GCEA, like a low-G ukelele).

    But the compensated bridge doesn't have the right compensation pattern. The E string in particular goes unpleasantly sharp when I play high on the neck.

    I'm a crafty sorta fellow and not scared of doing some woodwork. What would be the best way to go about constructing/modifying a custom-compensated bridge? Is that a reasonable thing to do or is it gonna be super hard? Maybe just take an existing bridge and sand it down?

    Or is there a bridge out there with some sort of adjustable compensation?

  2. #2
    Confused... or?
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    Default Re: Custom compensated bridge?

    Just for clarification, most of us would assume that the G & C are wound, while E & A are plain. And steel rather than ukulele nylon. And that "low-G" ukulele implies not re-entrant tuning, so that the A is the highest string, a 4th higher than the E. Correct?
    - Ed

    "What our group lacks in musicianship is offset by our willingness to humiliate ourselves." - David Hochman

  3. #3
    Teacher, luthier
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    Default Re: Custom compensated bridge?

    If you are using a very light string for your 2nd string, it's tendency to go sharp will be greater. You might try the next gauge up before you start cutting. I would suggest starting with an .017" plain. You might even try to go to a wound 2nd string, .022" or .020", and see what happens.

    Intonation problems are common if strings are not gauged right for a special tuning. For yours, I would start with 40, 26 or 28, 17p, and 13 or 14. This is assuming a carved top mandolin. For a flat top, I might go a shade lighter.

    Sometimes just turning the saddle or bridge around and regrooving it will get you to the right place.

    I use needle files and a miniature scraper to re-compensate a bridge. Some times a small tri-corner file comes in useful.

    If there is not enough wood left under the 2nd string to get the compensation you want, you might have to make a new saddle or bridge.

    If it's an adjustable bridge and you make a new saddle, start with a thick blank and drill your holes for the adjusting posts before you thin the blank, or it might split when you drill it.

    The hard part is figuring out the layout for the compensation. I start with the bridge 90 degrees to the strings, get the first string in tune, figure out which string needs to go back the most, then locate the others one at a time.

    You can make a trial run on a piece of maple or other hard wood before you go to work on a piece of ebony.
    Last edited by rcc56; Jan-21-2020 at 11:20am.

  4. #4
    Registered User amowry's Avatar
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    Default Re: Custom compensated bridge?

    Here's Frank Ford's description of how you calculate how far off your current compensation is. I use this method all the time, and it works great for small adjustments. You can use this to determine if your current saddle has enough "meat" to be compensated correctly or if you need to make a new saddle:

    http://www.frets.com/FretsPages/Luth.../compcalc.html

  5. #5

    Default Re: Custom compensated bridge?

    Correct about the tuning. It goes low to high, G being the lowest, then up to A at the highest.

    Also correct about the strings. I combined two sets of strings. the GCA strings are the GDA strings from a lightweight set, and the Es are the A strings taken from a heavyweight string set. I used to use wound strings for the E, but I think like the feel better this way.

    I've got some nice scrap hardwood lying around. Maybe I'll do some experimentation. Don't have any ebony but I have some bits of maple, hickory, and zebrawood which are pretty dense.

    I'll check out the frank ford link and do some reading...

  6. #6
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    Default Re: Custom compensated bridge?

    I've just looked up some string tensions. You can safely try plain strings as heavy as a 20, which will be about 19.5 lbs at E 330 Hz.

    Hard maple is reasonably suitable for a bridge.

    If you've got a local Woodcraft store, they often have chunks of ebony large enough for 2 or 3 bridges for just a few bucks.
    If they don't have any right now and you have a friendly local repair luthier who makes replacement guitar bridges from scratch, he might contribute a piece.

    If all else fails, pm me and I'll check my ebony scrap bucket.
    Last edited by rcc56; Jan-27-2020 at 11:10pm.

  7. #7
    Registered User sunburst's Avatar
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    Default Re: Custom compensated bridge?

    If you are starting with a blank, wide bridge top, you can go here to post #421 to see a very quick explanation of one method of determining 'compensation'.

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