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| Why bridges are shaped as they are http://w-ww.luthiersforum.com/forum/viewtopic.php?f=10102&t=4735 |
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| Author: | Michael Dale Payne [ Thu Jan 26, 2006 1:52 am ] |
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I own a Alverez Yairi WY1K It has a bridge that is a reverse "C" shape that only holds the saddle and the saddle is centered in its mass the pin holes are in a plate that is part of the bridge patch plate that protrudes through the top in the area that the pins are located Here is a real bad pic I pulled of their site, but I think you can see. 
I would think that a bridge that had a large area in front and rear would dampen the saddles energy. |
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| Author: | Laurent Brondel [ Thu Jan 26, 2006 2:07 am ] |
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This is how I understand it. The bridge is kind of an additional brace, reinforcing the X-braces, and also serves as anchor to the strings. Too big a bridge will suck energy out of the top, so less volume and "sound" but perhaps more sustain. There is pull in front of the bridge, but I do not think the bulk of the energy is there. If you add too much mass in front of the bridge I'm almost sure you'll loose a lot of sound. There should be enough wood in front of the saddle to prevent splitting, and this is very little since the saddle is angled and shouldn't follow the direction of the grain. One critical aspect of having a solid glue joint between the bridge and the top is to shape the bottom of the bridge to follow exactly the radius of the top, and not force the top to flatten at the bridge footprint, or force the bridge to adapt to the top's curve. One thing I learned also is that ebony or rosewood tend to oxidize rapidly, which is not good for a good glue joint, so I always lightly scrape (not scar) the bottom of my bridges before gluing. |
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| Author: | Michael Dale Payne [ Thu Jan 26, 2006 2:25 am ] |
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I agree with Laurent here. I believe that Yairi design was to address the bridge pull up issue the pin support is not an additional plate but actually part of the Bridge plate protruding through the top thus eliminating the some of the bridge mass and the pull of the stings in the back of a conventional bridge. Here are a couple of better pics of the Yairi direct coupled bridge.   |
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| Author: | Pwoolson [ Thu Jan 26, 2006 2:34 am ] |
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To me it makes logical sense that the mass of the bridge falls behing it, into the large open area of the lower bout. That's where you want most of the movement to occur. If you put much in front of the bridge, you be in the area of the cross of the X which would be unnecessarily doubling the bracing in that area as well as trying to move a very heavily braced area. Sort of why 12 fret guitars often sound bigger than 14 fret guitars. Because the bridge falls more in the open area of the lower bout. |
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| Author: | bbeardb [ Thu Jan 26, 2006 2:38 am ] |
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Here is a non traditional bridge. 
My unschooled thinking would be, if you want a bigger bridge, leave less bracing underneath so it's not over braced. I see no reason why bracing can't be on the top of a guitar... website here |
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| Author: | Mattia Valente [ Thu Jan 26, 2006 2:59 am ] |
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There's also this to consider: the front of the bridge is being pushed down, so the glue line's under compression there (and shear. always shear), but the rear of the bridge is being pulled up. The 'feet' analogy doesn't work because we're not designed to be glued to the ground! If we had similar forces on us, we'd want our heels firmly anchored, since the toes, well, they'd stay put anyway. The strain is on the glue joint at the back edge of the bridge. The reason bridges are 'bellied', as I understand it, is to increase the length of the glue line while minimizing the increase in mass, giving the bridge more to hold on to the top with. The Yairi design's smart, since the bit where the string tension is bearing on most (pins) is 'wedged in' physcially, and would stay put even without glue. The saddle holding bit still wants fairly maximal glue line length along the back edge, ergo the shaping like this. |
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| Author: | SonicAgamemnon [ Thu Jan 26, 2006 3:04 am ] |
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Instead of changing the bridge plate shape/size, perhaps a different type of glue (epoxy?) or glue mixture is needed, or a different surface prep. and/or clamping technique? I have been told that great sounding guitars are built on the edge of disaster-- very low tolerence levels, etc. In fact, I would be tempted to make the bridge *smaller* and resolve this stability issue some other way, using a stronger adhesive, etc. |
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| Author: | Michael Dale Payne [ Thu Jan 26, 2006 3:13 am ] |
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Epoxy would be a nightmare repair. |
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| Author: | Mario [ Thu Jan 26, 2006 3:15 am ] |
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I have a 98% success rate with my bridges. In other words, I've had 2 lift in 100. Both were on cedar tops... One of them only required some fresh hot hide glue snuck under and a light clamping to set it back, as far as I know. And go look at my bridge. Small, straight. Less than an inch wide. What most would consider a disaster waiting to happen. Good glue and good glue practices(go read the thread on cross-hatching to see my point of view) will take you far. |
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| Author: | SStallings [ Thu Jan 26, 2006 4:13 am ] |
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Mario: Is your bridge longer than a standard Martin bridge? Hard to tell from your website. I guess a related question is whether, assuming good glue practices, is there a minimum area that a bridge must have to withstand the forces from the strings? |
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| Author: | Paul Schulte [ Thu Jan 26, 2006 4:14 am ] |
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Mario, just took a look at your bridges, are theY a bit longer than 6"? They look about 6 1/4", or it my be that the width makes them look longer. |
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| Author: | Mario [ Thu Jan 26, 2006 4:28 am ] |
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The rectangular one are between 6- 6-1/8". The ones with the angled ends are 6" at the front and around 6-1/4" at the rear. About the minimum; there comes a point where you can't fit pins -and- a saddle on them <g> The old Gibsons were 15/16" wide, and that is pretty much it for a minimum. |
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| Author: | JJ Donohue [ Thu Jan 26, 2006 4:39 am ] |
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I've used Pyramid Bridges (6"x1") on 4 so far with no problems. My first had a failure 2 days after gluing but it was technique related. While I don't have the numbers nor the time in service that Mario has, there are no signs of failure so far. Now that I said that, the gods are sure to confound me! I use HHG exclusively and follow a rigid protocol in the gluing operation...good surface prep, fresh glue, work fast and clamp with moderate force. I seem to remember reading that Martin used Pyramid Bridges exclusively in the early days until they had separation problems. They "solved" it by going to the current belly bridge. I'll bet there's a lot more to the story. It's my belief that the 6x1 bridge area is sufficient if one's technique is sound and consistent. |
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| Author: | Michael Dale Payne [ Thu Jan 26, 2006 4:42 am ] |
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Wow  I just had an idea for a prototype that I think I will work on this year. A configeration somewhat like the Yairi direct coupling system except pinless.
In the past I have had several clients say they would prefer a pinless bridge except for the reputation that pinless bridges have for pulling up (warranted or not) This type of configuration with a "T" shaped plate for the sting balls that is inserted and glued through a mortised slot in the the patch plate and top eliminates that issue. I also see how this could help make locating the bridge and saddle location very easy. I think I could do this with out crossing any patend problems 
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| Author: | Pwoolson [ Thu Jan 26, 2006 4:58 am ] |
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Michael, epoxy releases with heat. It's an easier release than tightbond in my experience. |
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| Author: | Michael Dale Payne [ Thu Jan 26, 2006 5:13 am ] |
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I know it releases with heat. My experance it took more heat is my issue. I may have been rushing a bit but I had a repair on a dovetail neck reset and miss placed bridge that had been epoxied down. The bridge was tough but do-able, the neck was a reall nightmare It to had been epoxied in. |
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| Author: | Pwoolson [ Thu Jan 26, 2006 5:28 am ] |
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I can see where a neck would be hard as it's difficult to get heat into the joint. But my experience with bridges is that if I set an iron on them, they nearly fall off by themselves. |
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| Author: | Michael Dale Payne [ Thu Jan 26, 2006 6:40 am ] |
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About 220deg ro what? |
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| Author: | Alan Carruth [ Thu Jan 26, 2006 8:00 am ] |
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To expand a little on what Mattia said: If the strings came right off at the level of the top surface, the only stress on the glue line would be in shear. In 'The New Science of Strong Materials; or why you don't fall through the floor', the author shows how this sort of stress is distributed in a glue line. If you glue two sticks together and pull on them (which is the same thing) the stress is highest at the front and back edges of the glue line, as seen along the direction of pull, and low in the middle. The low level is set by the strength and elasticity of the glue. The area under the curve equals the total force. The joint fails if the stress at the leading or trailing edges exceeds the strength of the glue line. Making the joint longer along the line of pull puts more of the total stress into the low level part of the curve, and thus cuts down on the stress at the edges. That's why the 'belly' bridge holds the extra tension of steel strings where a classical-type bridge usually won't, even though the 'belly' has a smaller total gluing area. Of course, the strings _can't_ come off the bridge right on the surface of the top: you couldn't play the guitar! The fact that the strings are above the top puts a torque on the bridge: it's as if it's trying to rotate around the line where the saddle would hit the top, roughly. As Mattia pointed out, the glue line in front of the saddle is being compressed, and that would stay put even if there was no glue, if torque were the only issue. The back of the bridge is being lifted off the top, so the glue line there is taking a peeling stress. Very few glues are much very good at resisting peeling: once you get that edge loose the rest is a piece of cake generally. So, when you add up the shear stress and the peeling stress, you can see that the back edge of the bridge is the critical point. The front-to-back width of the bridge establishes the level of the shear stress, and the little bellcrank lever of the saddle top to bottom fulcrum, and the distance from there to the back of the bridge, sets the peeling stress. Length behind the saddle does you more good for peeling than length in front. Other than that, there's no particular reason not to put the saddle further back that I can think of. It's not going to 'damp' the sound for that reason, although, of course, you will need to use a bigger bridge. IMO, mass is more important then footprint area in terms of tone. Mass cuts down treble by limiting acelleration. It's easy enough to make a big, light bridge by using a less dense wood, such as walnut, and this can give you great treble response. For one thing, in it's fuunction as a top brace, it's reasonably stiff and light. |
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| Author: | CarltonM [ Thu Jan 26, 2006 8:01 am ] |
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It seems like a downside to the Yairi system would be that they're cutting a big ol' hole into a major sound-producing area of the top, and then plugging it with hardwood. It might be more structurally stable, but... |
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| Author: | Mattia Valente [ Thu Jan 26, 2006 9:20 am ] |
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[QUOTE=CarltonM] It seems like a downside to the Yairi system would be that they're cutting a big ol' hole into a major sound-producing area of the top, and then plugging it with hardwood. It might be more structurally stable, but...[/QUOTE] To be fair, that area in a 'traditional' guitar is wedged between 2 pieces of hardwood (Bridge plate and bridge itself), so in terms of mass, I don't think there's a huge difference, and if the fit is good, I don't see why it should be a problem... |
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| Author: | Michael Dale Payne [ Thu Jan 26, 2006 9:49 am ] |
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No material is lost in this area as the fit is press fit tight. so all material taken out by the slot is replaced with the t-plate that makes up the pin plate |
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| Author: | crazymanmichael [ Thu Jan 26, 2006 10:43 am ] |
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gibson uses/used a reversed belly bridge which put more mass in front of the saddle. the result seem to be that lifting bridges/splits along the pin line are more common than with the martin approach. the question could be asked whether it is a design or a quality control issue, and my guess is that it is a bit of both. |
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