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So as not to continue the hijack of the other bridge plate query.

I am a traditionalist and make my bridge plates just like most of you, Maple or Locust, slightly wider than my 1" bridge, beveled on the north & south, butted to the X-legs. I like the sound of my guitars and am not unsatisfied with any structural issue. I do not want to recommend any changes to tradition, only to think out loud what I have been thinking in my head.

I wonder if the reasons for the plate's traditional form can be attributed to factory practice and a small builder could find a bit of improvement by some changes.

As for the structural reasons of the plate, anti-rotation, cross-top stiffness, etc. I would like to substitute resonant Spruce for all those functions and relegate a tiny bit of hard wood for string-ball seating wear.

No, I have not tried any of this in practice, I barely have enough time to build traditional guitars between my repairs.

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I think you're right about original practice, which likely came from the 'how fast can I', rather than 'how good is it' mentality. Factory practice, as you said.

I've seen other people use spruce with a ball cap plate, but I've never played/heard one, so I don't have much to say. It seems reasonable to me that you could get a bridge plate both stiffer and lighter this way. But I've never tried, so I could just as easily be, ya know, wrong. I would imagine adding carbon fibre ala Gore would help too.

For my own, I've gone to the curved back ones as Gore suggests, and noticed an immediate improvement in the appearance of bridge rotation. At the cost of a few grams only. I'll stick with that probably until I go Full Gore...

Also, just read your comment in the other thread. I think the plate does a lot more than hold the ball ends. Even if it were only made of spruce the same thickness of the top, it would make the top 8x as stiff in the area, using the cube stiffness rule, notwithstanding material properties and the help of the braces. But I think it adds considerable strength.

Thanks for starting me off Ed.
Of course the plate adds stiffness, strength, but rotation can be controlled by placement of the X legs at the bridge wings, and at bridge center by means of tone bars and top thickness.
What got me thinking about this is the Torres guitar that RE Brune' restored that had no bracing in the lower bout, and one of the all-pine guitars that I built with a thicker than normal top and smaller than normal bracing.

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David, I lol'd because I thought you were trying to be funny as it seems like there has been a LOT of those discussions lol

Seems to me that butting them up would greatly increase stiffness.

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Pat

Of course the plate adds stiffness, strength, but rotation can be controlled by placement of the X legs at the bridge wings, and at bridge center by means of tone bars and top thickness.

Certainly true, however all those things will likely effect timbre more than small adjustments to the bridge plate IMO. But dactyl how would require some controlled experimentation I think.

I'm glad to see this come up. This is coming from the steel string persuasion, with pinned bridges, with hopes that it isn't too far off the topic, as it deals with the bridge and bridge plate.

For a couple of years I've been thinking about how we do bridge plates, and, from a structural standpoint, doing it wrong, I think. Looking at the "sandwich" of, from the top, the bridge, top, and bridgeplate, the stiffest component is the bridge, the BP is next, then the top. What we do have right is that the top is in the middle, with stiffer/tougher/stronger bits on either side of it. What I think we do wrong is putting the stiffest part on top. If for the moment we look at just the upward force of the ball end of the string, it's no wonder so many bridges peel up (not mine, not yet, knock on wood), though one could argue that it's the top and bridge plate peeling down. I drew out a crude sketch to illustrate. The curve of the top and other details are not entirely accurate, but it's the best I could do with the software.



The upper part of the sketch shows what we usually have on a steel string with a pinned bridge. The lower one shows an exaggeration of some of what happens when the bridge peels up (or the top peels down). The ball ends are pushing up on a small area that's not as stiff as the bridge on top. I'd wager that if the bridge plate were the stiffest of the three—bridge, top, and bridge plate—there would be less of a tendency for the bridge to separate.

Alvarez Yairi guitars address this problem with a two-piece bridge, one part for the saddle and the other for the bridge pins. The part for the pins has a flange under the top to keep it from pulling through, but it requires a considerable chunk of the top to be cut out for the top of the pin part to poke through.



Looking at the Alvarez Yairi design, it seems we could come up with something similar, where the major structure in the pin part would be entirely or mostly under the top. Of course we can assume that Yairi has put considerable effort into his design and in his eyes, it could well be THE solution.

What say ye?

Pat

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As I recall Haans used spruce as a brace plate with a strip of hardwood for the BP area.

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The name catgut is confusing. There are two explanations for the mix up.

Catgut is an abbreviation of the word cattle gut. Gut strings are made from sheep or goat intestines, in the past even from horse, mule or donkey intestines.

Otherwise it could be from the word kitgut or kitstring. Kit meant fiddle, not kitten.

Yep, everything changes when you push the extremes. With a really thick soundboard, a small pin plate is all you need. A larger one can still be used to equalize humidity expansion with the bridge and keep the soundboard flat in any condition, and in that case it can be very thin. AFAIK, this is the main purpose of the classical guitar bridge patch.

But also, you can think of the bridge-soundboard-bridge plate sandwich as a composite cross grain brace, where the cube rule of stiffness applies, so even the thin classical guitar bridge patch does make a significant difference. Honduran rosewood is a good bridge plate material, because it's plenty hard, and has extremely high Young's modulus. Even a thin piece, due to the spacing away from the bridge by the soundboard, will greatly increase the stiffness.

When going to the extreme of thin soundboard style, the bridge plate's stiffness role becomes much more important. In this case, it's probably better to have more than the stiffness of a cross grain hardwood plate to prevent bellying/bridge peeling. Including a layer of carbon fiber is good because it's stiff in both directions. Or two layers of softwood, criss crossed at 45 degrees to the soundboard grain.

Or just a softwood plate aligned the same as the soundboard grain, with a small, thin cross-grain pin plate, which also provides a bit of cross grain stiffness (limited by how much of it is continuous grain versus cut through by the pin holes). Having braces run underneath the bridge is another way to prevent excessive bellying when the soundboard is super thin. That's what I did here.


For medium soundboard thickness, it's still good to extend the bridge plate behind the bridge some, basically offsetting the belly back a bit from the bridge, where it won't peel at the joint. Though another thing I like is to taper the thickness of the bridge itself, so it's thin at the back edge, and can flex a little to dissipate the peeling force. Also keeps the bridge weight down, if you consider that to be a good thing.

I think Bruce and Matt Petros have been doing what you're suggesting for quite some time. Spruce plate with a small piece of ebony that resists wear from the ball ends.
They might be able to shed some light on your wonderings.

Thank you everyone for contributing! I am surprised a bit that my thoughts have not been attacked, but there is time for that yet.

I have made several guitars in the distant past with spruce plates. Certain Spruce can be quite tough and resistant to wear at the string balls if you use un-slotted pins that fit tight in the tapered holes, and string slots that minimize the tendency of the ball to try to wear at the edge of the hole.

My current interest on experimental guitars, as compared to traditional guitars, is to make the soundboard thicker and to minimize the bracing somewhat. These guitars tend to piano-like tone, which I like, but can lack robust volume. I have yet to experiment with the bridge plate, but may try something on a later one. On guitars with a thicker top, bridge rotation and bellying is not as much of an issue. I always lay out with pencil the placement of all the elements of the top to a fairly high accuracy, thus I can locate the exact position of the pin holes, and can make a minimal Rosewood plate. An alternate plan can have the small plate glued in after the bridge is glued on and the holes drilled.

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Man I sure hope that we don't give the impression that we are actually attacking anything.... That's never, well seldom.... my goal. Besides David I've always liked you and appreciated your contributions a great deal too so you are just going to have to put up with that.

Regarding being a naysayer of course my interest is serviceability. But you guys are bright guys, most of you..... (kidding of course you are all Einsteins.... and I'm Sarah Palin..... ) so you know when something that you are doing is going to result in some colorful language someday when another Luthier has his/her hand in your sound hole...... Man I had better go stifle myself....

Oh yeah regarding the Yari implementation of a bridge I've long thought that they knew what they were doing. Look at what happens to the break angle when the part with the pins is significantly lower than conventional bridges - pretty cool!

Regarding the Yari design: makes me wonder how much gluing surface we really need for a steel string bridge?

Somewhere (Trevor books?) I read about 45 cm2.

Hey Edzard - should have some pics for you that I will send to you next week when we get the parts back from annodization.

Don't know what Trevor came up with doing the math and applying the physics but let's talk about real life too regarding gluing surface.

Ultimately the amount of gluing surface that any bridge may need is also going to be a function of the care, envirnment, amount of use, and strings used. Guitars that are not permitted to dry out tend to keep their bridges much longer. Guitars with 12's also tend to keep bridges longer than guitars with 13's.

I know that we like to consider the perfect world but that's not what I see daily nor what your creations will likely see daily either if you sell or gift them. Folks neglect stuff.... an understatement.

Also very much related is how the bridge is glued on and with what too. It's not uncommon to see with f*ctory instruments up to 40% of available gluing surface not used because they don't clear the finish away any where close to the bridge foot print.... espically at that critical back edge....

Also regarding how much gluing surface a bridge will require even things such as using slotted pins and what your bridge plate is made out of have an impact here. A worn plate and slotted pins lead to brdge cracks between the pins and this can contribute as well to the birdge wanting to take a hike.

Regarding glues cold creep, glues that don't handle humidity well all can also contribute to the bridge wanting to come loose.

Here's another one - cedar tops. Sure we like em, I've built with cedar lots of times but when the bridge patch on a cedar top begins to fail cedar is well known for having lots of top wood ripped off when a bridge lifts. So as you can see material selection also plays into how well a bridge will stay put.

I'll even add how the top is braced, how stable the bridge area is and how much rotation is permitted - all real life factors that may skew the math but nonetheless reality for us.

In the Yairi design, the part of the bridge with the pins is installed from beneath the top and pokes up through the top, so stresses on that parts are mostly compressive. I'd guess that glue area here wouldn't be much of an issue. I think that's the beauty of his bridge design: glue surfaces that are in tension in a conventional design are now in compression.

Pat

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As for how much area is necessary, I'll relate my experience with a tipple. That's basically a ten-string uke with steel strings, triplets on the top and bottom with doubles in the middle. Anyway, it's a pinless bridge, about 7/8" x 4", with about 200 lbs of string tension (that's 57psi). I have to admit my first two trys didn't hold for very long(first failed bringing it up to pitch, second stayed on a couple of weeks), but when I finally got it right, it's stayed on for 5+ years.

That leads me to believe that a 1"x6" footprint(about 25psi) is about twice as big as it has to be.

While we're talking bridgeplate design, what is the current thinking on the PMTE? Does anyone else use them?

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Yeah, the Yari bridge has no bridge parts in tension, that's cool. Traditional it is not, that limits the design for sure.

I've never lost one of my 1x6 bridges glued with hhg, to my knowledge, so pulling up is hardly an issue for a well glued bridge of traditional design.
At issue is the heat of the car in which the guitar is stored.

Hesh, I do a lot of repairs too, all factory guitars use white glue, and they must be on a glue rationing program.

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Some pulled up bridges on newish Martins look to have about half as much glue as they should. Anything to reduce time to clean up squeeze out, I suppose.

Pat

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Yeah and not specifically Martin but many manufacturers leave up to 40% of the gluing area with the finish not cleared away.... It's often on the back edge area too which is where the real heavy lifting is done for a well attached bridge.

Then we have the imports that often use AMG (Asian mystery glue) that will not release with heat and moisture. Well it probably would release with enough heat but Lutherie shop tactical nukes are not yet available at Stew-mac or LMI...

I don't care what guitar factories do, the worse they are, the better it is for quality makers.
I quit looking at factory guitars a long time ago (repairs that force their way into the shop being the exception) and try to think through my own work independent of factory standards. I am above all that stuff now. (where is that "snigger-snigger" smiley?)

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I've got a 24.9" 13 fret 000 with a PMTE in finishing right now. Just wanted to see what would happen if I tied everything up real tight around the bridge and that seemed like a good way to do it.

As far as pulling up with HHG - I've had one come up and it was because I was too slow getting the vacuum clamp on and it partially gelled. Didn't completely fail but I could see the gap so I pulled it and re-glued it.

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