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Thread: Questions about bridge design

  1. #1
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    Default Questions about bridge design

    Besides playing the mandolin, I play an arch top guitar, so attention to the bridge is a natural interest for me. There is a lot of discussion here about the mandolin bridge, and certainly the correct installation precedes any judgment of quality. I currently play a “The Loar” LM-700 and it came with a “Cumberland Acoustic” bridge, but I am actually using the original bridge. The instrument required some neck repairs and by eye it looked like the Cumberland was not fitted quite right so I put it aside and refit the original bridge (that had never been shaped to fit the top). The Cumberland is a very nicely made bridge, the wood selection and cutting, the selection and installation of the hardware all are the best I have seen on imported instruments and aftermarket bridges. Based on the bridge’s critical role in the sound and performance of the instrument we seem to accept rather than question many elements of their design.
    For example:
    • Why do the feet taper on the inside rather than have a definite edge?
    • Why is the base symmetrical? The instrument isn’t.
    • Why are there corners, sharp edges and the cove routing?
    • Why are the adjusters so big?
    • How important is the weight of the bridge, or the base?
    • Is the material of the screw important?

  2. #2
    Mandolin user MontanaMatt's Avatar
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    Default Re: Questions about bridge design

    Check out the designs of the Brekkee original and tradional bridge for some elegant bridge designs. http://www.bridgerproducts.com/brekke_bridges
    http://www.bridgerproducts.com/about.../weber_designs
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    I may be old but I'm ugly billhay4's Avatar
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    Default Re: Questions about bridge design

    All good questions, but good luck on getting consistent answers.
    I will say that fitting the feet of a bridge to the top is probably the most important thing to do. This keeps the bridge from tilting and allow the energy of the strings to be imparted to the top in the most efficient manner. An after-market bridge will have to be custom fitted to an instrument as top shapes differ enormously. I believe Rob Meldrum's book (email him at rob.meldrum@gmail.com) addresses how to do this. There are several techniques that work well.
    Bill
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  6. #4
    Moderator MikeEdgerton's Avatar
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    Default Re: Questions about bridge design

    There is some great information on bridge design out there. One of my favorites is on the Murphy Blog:

    http://blog.murphymethod.com/category/mandolin-bridges/

    Frank Ford has some fitting information on his website www.frets.com:

    http://www.frets.com/FretsPages/Luth...t/fitfeet.html
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  7. #5

    Default Re: Questions about bridge design

    This subject has been the focus of my week because the bridge saddle on my mandolin cracked at the bass side. Now I have no experience swapping one bridge for another. What I did prove to myself was the importance of solid contact with the top. I had spent some few hours getting this right and was reluctant to start over. It so happened I have a new CA bridge but was hesitant to put it on my inexpensive import, plus it would have had to be shortened considerably.

    I lucked out and obtained a saddle with the correct hole spacing. This new part alone improved both tone and loudness of the mandolin. The wood is darker and looks denser than the cracked saddle, and it does not drop down from where the wheel rests, so it is thinner top to bottom. That was the only difference. Quite dramatic really for such a similar part.

    So I have become a true believer from first hand experience that a bridge has a very significant effect on tone.

    This kind of correlates to the bridge saddles on a Telecaster guitar. Believe it that brass has a different effect on tone than steel, and you can tailor tone accordingly, and this on an electric guitar. Tone transmission is a very interesting subject for sure.
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  8. #6
    Registered User fscotte's Avatar
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    Default Re: Questions about bridge design

    Because Loar did it that way.

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    Default Re: Questions about bridge design

    Quote Originally Posted by fscotte View Post
    Because Loar did it that way.
    Yes, that is exactly what the Cumberland guys did. but it certainly shouldn't stop there.

  10. #8

    Default Re: Questions about bridge design

    • Why do the feet taper on the inside rather than have a definite edge? It looks nice and is traditional
    • Why is the base symmetrical? The instrument isn’t. There's no need. Plenty of people have made asymmetrical bridges, it works fine but offers no distinct advantage.
    • Why are there corners, sharp edges and the cove routing? For ease of manufacture using the original methods (shaper, etc.)
    • Why are the adjusters so big? Usually they're not. Cheaper instruments usually have larger adjusters.
    • How important is the weight of the bridge, or the base? It makes a difference, not a big one. Structure (stiffness, grain direction) is more important.
    • Is the material of the screw important? It can be made out of steel, brass, or aluminum, which is a lot less massive and still works fine. Nylon is probably a little too floppy to work, but would be fine if you have something keeping the bridge from rocking like the interlocking bit in the bridges I make.

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    Adrian Minarovic
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    Default Re: Questions about bridge design

    Quote Originally Posted by Br1ck View Post
    This kind of correlates to the bridge saddles on a Telecaster guitar. Believe it that brass has a different effect on tone than steel, and you can tailor tone accordingly, and this on an electric guitar. Tone transmission is a very interesting subject for sure.
    That's very different thing from effect of mandolin bridges. On electric guitars the steel vs brass tone has to do with magnetic properties of the metal and mostly affect bridge pickup which is close.
    I swapped bridges quite a few times just to see how the sound changes and unless you do something dramatic (ultralight bridge or extra heavy) the change in tone is negligible Even using bone or antler cap didn't change tone at all. IMO, the cheap bridges if setup properly will sound good (unless they break). They got the bad reputation mostly because they are commonly poorly fitted and setup from the factories. And more often than not they break because the person doing the setup removed wood from saddle to lower the bridge (at the wheels) and made it too weak to hold the load. I've seen few that had quite a bit runout in wood but cracked most likely because someone cut them too thin.
    Adrian

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    Default Re: Questions about bridge design

    I have never played or worked on a The Loar 700 but I understand that they don`t have any tone bars and when fitting a bridge to the top there might be some very slight sagging in the top when strung up under string pressure so using the "sand paper" method of fitting a bridge might not be a perfect fit even though it may look correct when not under string pressure...I have found this to be true on a few less expensive mandolins...I'm sure a lot of folks have their own way of correctly fitting a bridge but some others will say a perfect fit isn`t necessary...Some times fitting a bridge perfectly will take quite a long time...

    Willie

  15. #11

    Default Re: Questions about bridge design

    I'm sure fitting a bridge once you've done a hundred goes much faster that fitting your first, which took quite a while. I had a go at leveling the frets too. It took three or four tries because I was being conservative. Now I have a feel for the process, it goes much quicker.

    I agree that fitting the feet to the top is the most important aspect, as it made a huge tonal difference, but the density of my new saddle had a very audible effect too. The more I fiddle with mandolins, the more I realize every aspect is more critical than it would be on a guitar.
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    Default Re: Questions about bridge design

    I tried many years (too many) fitting them by hand, and while I thought I was getting better, I never fit one as well as with a jig like the SM or the CA designs. Considering the investment is less than the price of a nice bridge, I was either embarrassingly stupid, cheap or both.

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    Default Re: Questions about bridge design

    Quote Originally Posted by Willie Poole View Post
    I have never played or worked on a The Loar 700 but I understand that they don`t have any tone bars and when fitting a bridge to the top there might be some very slight sagging in the top when strung up under string pressure so using the "sand paper" method of fitting a bridge might not be a perfect fit even though it may look correct when not under string pressure...I have found this to be true on a few less expensive mandolins...I'm sure a lot of folks have their own way of correctly fitting a bridge but some others will say a perfect fit isn`t necessary...Some times fitting a bridge perfectly will take quite a long time...

    Willie
    I have lot of these middle level mandolins, an Eastman 504, a couple of M Kellys that are over 10 years old, a Loar 400, and a 700 (both without tone bars.) I could tell you about the defects of these Loar mandolins, but weakness of top is not one of them. Some will say that the bars in the top are "tone bars" and offer no strength, but to be honest they must offer some. I assume the luthier that designed this instrument compensated for the lack of tone bars, and I was attracted to them looking for something with an f hole sound that leaned toward the oval hole instruments.

  18. #14
    Registered User 108 Mile's Avatar
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    Default Re: Questions about bridge design

    I think you never get a perfect fit if the top has been marred or damaged. Click image for larger version. 

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  19. #15
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    Default Re: Questions about bridge design

    Why larger thumbwheels? They are a heck of a lot easier to adjust. Do larger thumbwheels have an effect on the tone? Sounds like another subject for endless debate.

    I've made bone caps for bridge saddles and found they did influence both the tone and the sustain of the instrument.
    Aluminum bridge saddles in the style of the briefly used Gibson 1921 design produce an interesting result.

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    Default Re: Questions about bridge design

    Quote Originally Posted by Doug Goodhill View Post
    I tried many years (too many) fitting them by hand, and while I thought I was getting better, I never fit one as well as with a jig like the SM or the CA designs. Considering the investment is less than the price of a nice bridge, I was either embarrassingly stupid, cheap or both.
    I started with the SM jig, I prefer to do it by hand and have not used it in years. Everyone is different and that's why this site is so great.
    THE WORLD IS A BETTER PLACE JUST FOR YOUR SMILE!

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  22. #17

    Default Re: Questions about bridge design

    Quote Originally Posted by squamish5 View Post
    I think you never get a perfect fit
    Fixed that for you...

  23. #18
    Registered User 108 Mile's Avatar
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    Default Re: Questions about bridge design

    FIFY...... how did you do that Marty?

  24. #19
    Adrian Minarovic
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    Default Re: Questions about bridge design

    Quote Originally Posted by squamish5 View Post
    I think you never get a perfect fit if the top has been marred or damaged. Click image for larger version. 

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    Repair by steaming or patching/filling the surface is one posibility.
    Otherwise chalk fitting is your friend...
    Adrian

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    Default Re: Questions about bridge design

    Adrian, When I explained fitting a bridge using the chalk (powder) method they just laughed at me and thought I was crazy...I have also used a contact gauge to get a good fit but that is another story....

    Willie

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  27. #21
    Adrian Minarovic
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    Default Re: Questions about bridge design

    Quote Originally Posted by Willie Poole View Post
    Adrian, When I explained fitting a bridge using the chalk (powder) method they just laughed at me and thought I was crazy...I have also used a contact gauge to get a good fit but that is another story....

    Willie
    Let them laugh...

    BTW there is one even easier method for really scarred tops (I don't do it this way but few folks have done it)... using thin coat of epoxy (mixed with fine ebony dust) on bottom of the base in place of the gaps and press it (string pressure works best) against the top (use thin foil to protect the top) and the result is just perfect fitting surface (after cleaning the messy squeeze out).
    Downside to this is that if the bridge needs to be moved the precise fitting won't allow it but if you always use the same strings and the position is precise for good intonation this is no problem.
    Adrian

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    Default Re: Questions about bridge design

    I attempted that epoxy method one time and messed everything up, I think using masking tape on the top to keep the epoxy from sticking was the culprit...I didn`t do this on any of my "go to" mandolins, I just did as a trial....

    Thanks for the advice though, I try to remember all of the little suggestions that I read here on the Café, for me some work some don`t...

    Willie

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    Default Re: Questions about bridge design

    You could use waxed paper for the epoxy method also. It doesn't tear as easy as foil, is fairly thin, and doesn't stick to things nor will let the epoxy thru.
    THE WORLD IS A BETTER PLACE JUST FOR YOUR SMILE!

  30. #24
    formerly Philphool Phil Goodson's Avatar
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    Default Re: Questions about bridge design

    I used the epoxy method with a Michael K. mando several years ago. Used Aluminum foil to protect top. Worked very well!
    Phil

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    Default Re: Questions about bridge design

    Epoxy! Brilliant new piece of info for me to file away.
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