Bridge shapes

[christoph.penny]

Before I fitted my eagle shaped bridge, I wasn't sure why most bridges were the standard shape, now after having a hard time fitting it, I realise that there a standard shape because of fitting them, is my theory correct please

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[Silly Moustache]

I'm guessing but I think that most bridges were bar or pyramid, until guitars became rhythm boxes and needed heavier guage strings -late '20s, early thirties?

[murrmac123]

There is no standard shape ... unless you are maybe thinking of a Martin-style belly bridge as a "standard shape". The reason you had difficulty fitting your bridge was because of your inexperience in doing this kind of work.

The size, ie the width of the gluing area of the bridge is, or should be, determined by how much glued area is necessary to withstand the tension of the strings. The individual shape is determined by the aesthetic preference of the luthier.

No matter how individualistic the shape of the bridge might be, I cannot imagine that "ease of fitting" would even remotely be a consideration in determining the desired shape.

[Ned Milburn]

Originally Posted by christoph.penny

Before I fitted my eagle shaped bridge, I wasn't sure why most bridges were the standard shape, now after having a hard time fitting it, I realise that there a standard shape because of fitting them, is my theory correct please

Sent from my XT1021 using Tapatalk

To a degree, you are correct.

A bridge must STRUCTURALLY be strong enough to hold and disperse the great amount of pressure exerted on it. In an x-braced guitar, the bridge wings should overlap the underlying x-braces. And front to back, the bridge must be wide enough to effectively avoid undue torquing of the soundboard which leads to a depression in front of the bridge and a strong convex doming behind the bridge.

And since so many of existing guitars are build in factories, it is quicker & simpler (ie: cheaper) to make a simple shape, rather than a complex shape.

For hand made guitars, an interesting bridge shape can help create interest in the guitar itself, and the extra time necessary is not as detrimental as in a large volume production setting.

[CaffeinatedOne]

The primary consideration when designing or installing an acoustic guitar bridge will be how well or efficiently it will facilitate the vibrations from the strings to travel into the soundboard, causing it to vibrate as well. That's it.

Sounds simple but it is not simple. It involves a fair amount of physics, both to arrive at an affordable, efficient means of energy transfer and to withstand the forces on the bridge over time.

The "standard" acoustic guitar bridge (such as the Martin bridge style) became standard only because it works, it is simple and affordable to make, and when properly installed it withstands the forces caused by string tension, humidity changes and so forth for a reasonably long period of time. There is nothing sacrosanct about the Martin bridge style - but it is pleasing to the eye and lends itself well to mass production.

Your eagle design is more or less an equivalent, having a fair amount of gluing surface, a mass about the same as a Martin bridge, and enough extra meat about it to allow installation of a saddle without being likely to create weak areas that will invariable crack over time. Is it "good" or "better" than other designs? Beats me, but if it has the basics and is properly installed, it's likely to work fine.

Proper installation may take a bit of fine work, as you presently have a rough gluing surface. If there are chips and an irregular top wood surface, it may be a good idea to use a router to create a uniformly flat surface and, if the wood has been thinned significantly, you may want to install a patch to restore the gluing surface to the proper height. So you can see that a simple job can get more complicated pretty quickly.

Click on this link: Examples of Guitar Bridges on Pinterest to see some pictures I found by doing a pinterest search of acoustic guitar bridges. You can see that the designs are all over the place. For an extreme example, look at floating bridges such as on a gypsy jazz guitar like a Gitane. There are many ways to do this, but any successful design should have the basics - affordability, efficiency, durability.

[redir]

Just don't do the Gibson reverse belly bridge thing, dumbest design ever.

[Rodger Knox]

Originally Posted by redir

Just don't do the Gibson reverse belly bridge thing, dumbest design ever.

It's a good design, they just put it on backwards!

[Alan Carruth]

The 'footprint' area of the bridge is less important in some ways than how it's shaped. In particular, making the bridge wide, that is, deeper along the line of the string pull, goes a long way to reducing the maximum stress along the back edge. Since this is where they start to peel up when they go adding the 'belly' to the old 'bar' bridge made the whole thing much more reliable: it probably would not have been as effective if they'd just made the whole thing bigger in every dimension to get the equivalent glue area. Classical guitar bridges actually have more footprint, but will peel up quickly if you put on steel strings. The footprint isn't the only thing at work here, of course; top thickness and bracing come in too, for example.

[Bruce Sexauer]

I continue to be surprised when I see bridges with points on their trailing edges. This concentrates the stress at the tip of the point and should contribute to both glue failure and top distortion leading to cracking. And yet that doesn't often seem to be a problem. Perhaps that is because many such guitars also have a thicker top that I would expect. There is a lot to be said for bridge templates in the rectilinear to elliptical range as far as handling stress efficiently is concerned.

[dekutree64]

Originally Posted by Bruce Sexauer

I continue to be surprised when I see bridges with points on their trailing edges. This concentrates the stress at the tip of the point and should contribute to both glue failure and top distortion leading to cracking. And yet that doesn't often seem to be a problem. Perhaps that is because many such guitars also have a thicker top that I would expect. There is a lot to be said for bridge templates in the rectilinear to elliptical range as far as handling stress efficiently is concerned.

Actually you can do this with a thin top as well, as long as the bridge plate extends some distance behind the bridge. Then if the soundboard is going to bend sharply under tension, it will be at the edge of the bridge plate rather than the bridge, so the bridge joint is protected from the peeling stress.

I use artsy bridge shapes with points on them, and the trick to fitting them is to either glue before finishing (which makes it difficult or impossible to do gloss depending on the bridge shape), or treat them like an inlay.

Position the bridge exactly where it should be, and score around it with a sharp pointed scribe (a knife isn't accurate enough because the blade width offsets the score mark a small distance). Use a router to clear away the finish inside the score line. Then give it a light scraping to smooth out any roughness left by the router, using a razor blade and chisels as miniature scrapers to get into the corners as best you can. Then glue the bridge by whatever method you like.

[Bruce Sexauer]

I have been a fanatic re getting my bridge plate and my bridge into size harmony, so it didn't occur to me that he bridge plate could be used to mitigate the problem I see. Of course you are completely right . . . but the cost is expending both mass and stiffness; not actually the end of the world, but something I work to avoid.

Lately I have been questioning my priorities a bit. I have treated "the work" as though getting the maximum performance possible from a guitar was a worthy life goal, but increasing I see that most people are very happy with a guitar that works 80 or 90 percent as well as it might. I struggle with this realization.

[Ned Milburn]

Originally Posted by Bruce Sexauer

I have been a fanatic re getting my bridge plate and my bridge into size harmony, so it didn't occur to me that he bridge plate could be used to mitigate the problem I see. Of course you are completely right . . . but the cost is expending both mass and stiffness; not actually the end of the world, but something I work to avoid.

Lately I have been questioning my priorities a bit. I have treated "the work" as though getting the maximum performance possible from a guitar was a worthy life goal, but increasing I see that most people are very happy with a guitar that works 80 or 90 percent as well as it might. I struggle with this realization.

Ha!! Good point!! Not everyone has the driving skills to be able to use the extreme capacity of a Porche. Most people's driving skills are limited to the capacity of a Dodge Calibre... ;-)

[dekutree64]

Originally Posted by Bruce Sexauer

I have been a fanatic re getting my bridge plate and my bridge into size harmony, so it didn't occur to me that he bridge plate could be used to mitigate the problem I see. Of course you are completely right . . . but the cost is expending both mass and stiffness; not actually the end of the world, but something I work to avoid.

There are plenty of ways to reduce mass in the bridge area to counteract the larger bridge plate, but the larger area of stiffness in the center should indeed affect the tone in a way that can't be counteracted. But is it good or bad? Probably depends on everything else, just like every other variable I'd love to hear your thoughts on it, if you feel like writing.

Lately I have been questioning my priorities a bit. I have treated "the work" as though getting the maximum performance possible from a guitar was a worthy life goal, but increasing I see that most people are very happy with a guitar that works 80 or 90 percent as well as it might. I struggle with this realization.

That's the advantage of living in this era of high global population Even if only one in a million people can appreciate taking something to the highest possible level of performance, that's still 7000 potential customers out there. And even if there were none at all, it's still a worthy personal goal... just not financially sustainable to make a large number.

My own approach is a "whole package" balancing act... perfect playability should be a given. Tone is what makes it worthwhile to craft these things one by one in the first place. But the feel of the instrument is also really important to me. The overall weight, the texture of the surfaces, the softness of the edges where it contacts your arm and body. I won't add extra side and neck mass even if it would improve the tone a bit, because the tradeoff in feel is not worth it. And beauty is not a totally superfluous thing to me either, so even if my bridge shapes aren't the pinnacle of functional design, the difference is small enough that I do consider it a worthy tradeoff.

[rogthefrog]

Originally Posted by christoph.penny

Before I fitted my eagle shaped bridge, I wasn't sure why most bridges were the standard shape, now after having a hard time fitting it, I realise that there a standard shape because of fitting them, is my theory correct please

Sent from my XT1021 using Tapatalk

Shape being three-dimensional, one thing to check is whether the radius of your top matches the radius of your bridge. If your top has a 15-foot radius and the bottom of your bridge has a 25-foot radius (flatter), then you won't be able to glue both ends of the bridge onto the top at the same time--the bridge will be rocking in place.

[Bruce Sexauer]

Also, the top surface of the bridge must be shaped to interface with the clamping system in such a way that the whole footprint is closed under pressure. And they look so simple!

I use a relatively flat top, around 45' radius, but I make no allowance for the curvature in my bridge; it is flat. As is my bridge plate, and there is nothing there to resist the top flattening against the bridge. Nor would there be if it were 25".

My usual take on bridge weight is that lighter is better. Thus there is no way to mitigate a heavier bridge plate. The only reason I see to make a heavier bridge is to promote balance through "compression", which is similar (if not the same) to limiting response. I consider that a band aid, and prefer to build even response into the basic structure. Since you asked.