Gluing warped back plates together

[MaineGeezer]

I've got some incredible yellow birch for the back and sides of the guitar I'm currently building. Probably because of the wild grain, the back plates have quite a curve to them. I've had them pressed flat for a couple of months, but there has been little or no improvement. Because of the way bookmatching works, when they are aligned for gluing one curves up and the other curves down, making things even more difficult.

Is there any trick to gluing plates like that, or do I just line them up as best I can, pile on the weights, and hope for the best?

[tippie53]

Usually the braces will fix that. I thickness the backs to about ..095 then brace in the proper disk
jh

[JLT]

You might want to make the back reinforcing strip (the piece with the grain that's 90 degrees to the back plates) a little taller than usual. That will help the stiffness there, and I doubt that it will affect the sound very much.

And like John says, the braces will help.

[Bob Gleason]

Because I sell sets, I have lots of experience with warped wood. In order to show the color in wood for web photos, I have to wet the wood. Alcohol or naphtha flashes off too fast for doing lots of photos, so I have to use good old water. Every single set warps when Ido that. When I'm done with the photos, I spray both sides of the wood with water and then dead stack it, weighted, on concrete overnight. The next day the sets will be straight again. When I get sets that won't stay straight, I simply don't use or sell them. You need to start your projects with good, stable wood. Too much work goes into an instrument to gamble on warped wood.

[MaineGeezer]

Bob:
So I might try wetting them, pressing them flat, letting them dry, and see what the result is?

I would feel a lot more confident about gluing them together if the edges started off more or less aligned, instead of ( and ).

[Bob Gleason]

That's right. If they don't stay reasonable flat on their own after wetting, weighting, and drying, then they will always be fighting the bracing and the center joint. Not a good thing! Especially in view of seasonal weather changes. That's my experience. Good luck with your project.--Bob

[MaineGeezer]

Wetting, flattening, and drying seems to have worked. Thanks Bob.