Is bridgeplate nessecary with a pinless bridge?

[redir]

Originally Posted by charles Tauber

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.

What I mean is I have seen that extend to the bridge itself. The telegraphing is basically deformation between each fan and when that extends to the bridge I have seen it start to delaminate such that for example you can fit a piece of paper under the bridge between the fans but not right over the fans. I imagine a patch would stiffen up the foot print so that would not happen, especially on a steel string.

[Alan Carruth]

Yes; one of the functions of the bridge plate is to reduce the stress riser at the back and front edges of the bridge, IF it extends beyond the bridge footprint. Usually Classical bridge patches end at the bridge edge, which makes the stress riser worse.

Thanks to Charles Tauber for the information on Gordon's book, and explaining it better than I did.

[dekutree64]

No, you don't have to use a bridge plate. But that doesn't mean you for sure shouldn't. Depends on the soundboard thickness around the bridge, bracing pattern, and wood used (peeling is much more a problem on cedar/redwood than spruce).

Originally Posted by Alan Carruth

Yes; one of the functions of the bridge plate is to reduce the stress riser at the back and front edges of the bridge, IF it extends beyond the bridge footprint. Usually Classical bridge patches end at the bridge edge, which makes the stress riser worse.

Thanks to Charles Tauber for the information on Gordon's book, and explaining it better than I did.

The perfectly matched plate might still help prevent peeling, though. Think of the soundboard as a piece of double stick tape... if you stick the bridge to one side of it, it can be peeled off easily. But if you sandwich it between two pieces of wood, then it becomes much more difficult to get either of them off, because the tape can't bend as it peels, so the joint has to fail all at once.

Of course it's more complicated in the real world since the soundboard is a lot stiffer than a piece of tape, and the bridge plate is not infinitely stiff so it will still allow some peeling to happen. But I think the analogy is still valid.

[printer2]

Because of the bending moment with the front of the bridge in compression I would think the rear would be under more stress than the front. A useful diagram on the stress.

[charles Tauber]

Originally Posted by printer2

Because of the bending moment with the front of the bridge in compression I would think the rear would be under more stress than the front. A useful diagram on the stress.

Compression at the leading edge and tension at the trailing edge. And that's why bridges always lift/"peel" from the trailing edge.

[Alan Carruth]

Right. Think of it as a combination of two, as shown by printer, but different. There's a shearing force, which is what you'd get if the strings were right on the face of the top, and that's as shown. The torque load acts around a 'centroid' between the saddle and tieblock, and is more or less a diagonal that is pulling up behind the centroid and pushing down in front. Down force doesn't bother the glue line unless it's sufficient to crush the wood. The actual force on the glue line is the sum of those. It's much higher along the back edge than along the front, so that's what sets the limit of the load the bridge will take before it comes up.

[printer2]

Oh, I never noticed the arrows when I posted the picture.