Laminated bridge plate trouble

[KingCavalier]

I'm trying to make a bridge plate for my current build and thought I might a laminated one. I glued a piece of hard Maple to a piece of Andaman Padauk using fish glue. Both pieces are rift sawn and I ran the grain in the same direction. I sanded the Padauk to around 3/32 and the Maple to around 1/32. I glued one in my go-bar desk with a radius dish and the other was clamped flat between two boards.

Both pieces cupped badly after I removed the clamps and I'm not sure why.

As always any help would be greatly appreciated.

SA

[clinchriver]

Probably moisture from the fish glue. Very thin bridge also.

[charles Tauber]

You may have noticed that commercial plywood is always made with an odd numer of plies. You've discovered why: differential wood movement.

[Tom West]

I think you would have more luck using epoxy. Hard to glue different woods of this thickness using water based glues due to movement from water absorption.
Tom

[jeff crisp]

If you have a thickness sander you could try sanding the bridgeplate to thickness after you have glued. Also if running the grain in the same direction try skewing the grain a little.

Jeff.

[John Arnold]

I have to ask why two different thicknesses were used. I believe that is at least part of the problem. Glue swells the wood on the side it is applied, and clamping for an extended period (several days) should eliminate that as a factor.

[KingCavalier]

Thanks for the help everyone

Originally Posted by John Arnold

I have to ask why two different thicknesses were used. I believe that is at least part of the problem. Glue swells the wood on the side it is applied, and clamping for an extended period (several days) should eliminate that as a factor.

John, I guess the reason for the different thickness is mainly because I have no idea what I'm doing

I like the idea of the Padauk but I was worried about it splitting. I thought if I used a thin layer of Maple on top that would help. I might try one more time at full thickness and thin it after as suggested.

Thanks again to all.

SA

[LouieAtienza]

Different woods will absorb moisture at different rates. IIRC there's actually is a woodworker's "hygromter" made with two thin pieces of dissimilar woods (I can't remember which) glued together, and this piece will bend a certain direction based on the relative humidity...

As Charles mentioned, having an odd number of layers helps, especially if the outer layers are the same material. The outer layeres don't necessarily need to be same thickness. In fine casework where veneers are used over a core material, both sides are always veneered, even if the hidden side uses a lesser grade veneer, to "balance" the piece.