Is bridgeplate nessecary with a pinless bridge?

[folkepudas]

Im thinking of making a pinless bridge on my next build. Do you still need a bridgeplate or is it unnessecary? Do you alter any other things when using à pinless bridge?

Best regards FolkePudas

[mirwa]

You don't need a bridgeplate

Steve

[folkepudas]

Thanks Steve!
I've seen some experienced builders who uses bridgeplates though, like Greenfield for example. What would the reason be for that? Doesnt it just add extra weight?

[mirwa]

You can add one if you wish, adding a bridgeplate to a pinless bridge adds mass to the area in question, it also adds stiffness to the soundboard.

It's up to you to decide if these are qualities that you are after

Steve

[Frank Ford]

I would not make a steel string guitar with*a pinless bridge and no bridge plate. The plate adds stiffness under the bridge and helps keep the bridge glued on. I would absolutely run the bridge plate grain parallel to top grain for that very reason.

Bridge glue joints need not only tensile and shear strength, but "peel strength," a most important consideration when gluing thin flexible things to heavy things trying to pull themselves off. . .

[Quickstep192]

Originally Posted by Frank Ford

Bridge glue joints need not only tensile and shear strength, but "peel strength," a most important consideration when gluing thin flexible things to heavy things trying to pull themselves off. . .

Pinless bridges look cool, but I wonder how reliably a bridge can really be glued to spruce. I just did some test glueups on a piece of spruce and although the glue held well, when I forced it to separate, strands of spruce peeled up. I know it's done, but I wonder about the long term viability of it. Does string tension act differently on a pinless bridge because of the string angle going back more or less in the same plane as the top rather than angling down through the pin hole?

[charles Tauber]

Originally Posted by Quickstep192

Pinless bridges look cool, but I wonder how reliably a bridge can really be glued to spruce.

Pinless steel string bridges have been around a while now and there are plenty of examples of them. Some are now 30 or 40 years old. Some have had the bridges come off, just a pined bridges have: they are just reglued and the instrument continues on.

Historically, fretted string instruments had pinless bridges, with the strings tied to the bridge. Granted, those were with non-steel, lower tension strings, but there is a long history of pinless bridges.

[troutmiester]

Pretty sure Lowden uses one on his guitars....

[Ned Milburn]

Agreed 100% with Frank. A bridge plate can help distribute and disperse the torquing/twisting pressures of the string tension.

Lowden guitars pinless bridges are well glued and so far I haven't seen one pop off.

I use a pinless bridge on my Evo design guitars with a spruce bridge-plate. The bridge itself has more area in its footprint than a Martin standard bridge style, so I expect there won't be any troubles with the bridge for decades into the future.

[LouieAtienza]

I would for the exact reason Frank mentions. I think Breedlove may use hidden fasteners on some of their pinless bridge designs, if I remember correctly.

One reason to go pinless in that it offers flexibility in bracing, since one does not worry about the pins interfering with bracing placement. I believe it is one reason why Michael Greenfield does it. Another design, while not truly pinless, is from Jeffrey Elliott, where steel pins sit within counterbores that hold the ball end, and go through the bridge and top into a tiny dense hardwood strip inlayed into the bridge plate. Greenfield has a few designs that use lattice bracing (I believe mainly his fanned fret guitars) and Elliott has a hybrid classical/X bracing, where the X brace acts as sort of a buttress over the fan bracing.

[mirwa]

Originally Posted by folkepudas

Do you alter any other things when using à pinless bridge?

I missed this part of your comment earlier, if you decide not to use a bridgeplate, nothing else requires strengthening, you just build it like normal.

Many hundreds of thousands of guitars exist in the market with pinless bridges and no bridgplates.

Again, this is a personal choice, where you way the pros and cons and make your own decision.

Steve

[Alan Carruth]

Qjickstep192 wrote:
"I just did some test glueups on a piece of spruce and although the glue held well, when I forced it to separate, strands of spruce peeled up."

Congratulations; you made a good glue joint. The problem was not there, but in the fact that you put enough stress on it to exceed the peel strength of the spruce along the edge. Once you've done that no glue line will hold.

Theres a book called 'The New Science of Strong Materials' that gets into this. In one section he looked at the stress in a glue line in shear between two pieces of material. The stress varies in different parts of the joint, being highest at the leading and trailing edges, and lower, and practically level, in the middle. The stress in the center is probably a function of the glue line, and the area under the curve has to be enough to take up all the strain on the joint. The longer the joint is along the line of the pull the more of the strain will be taken up by the level area in the middle, and the less there will be at the peaks along the edges. It's the peak levels that determine when the thing pulls up; once it starts the levels in the rest of the joint just get higher, and it wasn't strong enough before so it keeps going.

That's why the 'belly' bridge works. It actually has less glue surface than the 'bar' bridge on a lot of Classical guitars, but if you put steel strings on a Classical the bridge won't last long. One reason it works is that the belly reduces the peak stress along the back edge out of proportion to the additional area, and they stay down pretty well.

I've used something like the Elliot style bridge for several years now on some projects, where the flexibility of brace placement it allows was useful. Since I hadn't seen the original, I made mine a bit differently. On mine the pin in the center is not actually under any great load, it's simply there to keep the ball of the string from flipping sideways. I usually use 1/16" brass rod stock, and it only goes into the bridge itself. The ball is captured by the edge of the hole, which is reinforced with a piece of thin wall brass tubing so it won't wear. This has been quite effective, holding the strings well while making them easy to change if you get all the angles right. The bridges themselves are pretty much the same size as my usual pinned belly bridge, and so far I've had no problems with them coming off. Knock wood....

[redir]

I think I would want to have a bridge plate on a steel string guitar too. On classical guitars I have seen the a tops fan bracing telegraphing to where the top distortion was leading right up to and under the bridge. A bridge plate would prevent that.

If I understand Alan correctly then the dead center of the bridge is where the shear strength is nill. That's basically where the pins are. So in a pinless bridge where the string end is at the very tailing edge of the bridge where the shear strength is greatest (and I assume equal to the leading edge) it would indicate bad design. But suffice to say, the glues used in guitar making are pretty good stuff.

[charles Tauber]

Originally Posted by redir

If I understand Alan correctly then the dead center of the bridge is where the shear strength is nill. That's basically where the pins are. So in a pinless bridge where the string end is at the very tailing edge of the bridge where the shear strength is greatest (and I assume equal to the leading edge) it would indicate bad design.

You've misunderstood.

Shear strength is a property of the material (glue, wood, etc.). The shear strength is not (nil) zero. Shear stress is a measure of the applied loads.

The shear stress in a glued joint is not constant across the entire glued surface. It is highest at the two edges of the joint, leading and trailing. It is less, but not zero, towards the middle of the joint.

Alan points out that the further the trailing edge is from the center of the glue joint, in the direction of the application of force, the more of the deformation of the joint is countered by the center area of the joint, reducing the shear stress at the extremes, the leading and trailing edges of the joint. He gives the "belly" bridge as a practical implementation of that. In other words, making the bridge wider parallel to the strings - the direction of the applied force - reduces the shear stress at the leading and trailing edges of the bridge.

Purely in shear, the applied forces would attempt to drag the bridge across the surface of the top, glue and wood strength preventing it. Assuming rigid materials, it wouldn't matter where on the bridge the strings are attached, the result would be the same.

The bridge and top are not purely in shear, however, bending is also involved, introducing a moment (torque). For that, it does matter where the forces are applied, as you've suggested. The bending moment, however, is much smaller than the applied shear force.

The bottom line is that people have been successfully using pinless bridges for long enough to show that it works sufficiently well, regardless of what theory does or does not predict.

J.E. Gordon's book, The New Science of Strong Materials or Why You Don't Fall Through the Floor, is a fun read aimed at a general audience. So is his book, Structures or Why Things Don't Fall Down.

[charles Tauber]

Originally Posted by redir

On classical guitars I have seen the a tops fan bracing telegraphing to where the top distortion was leading right up to and under the bridge. A bridge plate would prevent that.

It isn't uncommon for classical guitar makers to include a thin spruce pad under the bridge that runs nearly the entire width of the guitar body. Its use does not prevent the fan bracing from telegraphing through the thin top.