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[BKARTS] Gluing (Layering) boards to prevent warpage



Hi Betty... You will be better off to align the grain in all layers of board in the same direction. The theory of opposing grains works on the plywood example but even 1/8 inch plywood is made of at least five layers and still is prone to a saddle curve.
As to number of layers there is nothing magical about three. You should consider that the moisture introduced by the glue must wick out of the sandwich before the board is truly stable. More layers means more moisture means longer time to cure.
If you want the finished board, before covering, to be flat then with three layers of two thicknesses the important point is that the two outside boards be the same, like so: A B A.
It does not matter if A or B is the thicker and it is always a good idea to glue all facing board sides: Ax xBx xA where x is applied glue.
If you glue them up A A B then the dried board will pull towards side A or B, whichever is the thinest of the two. This tendency of the laminate to pull towards the thinner board can be useful in balancing the forces on the boards after covering and paste downs. Say with a vellum binding.
With two boards of the same thickness, A A, then you should be careful to glue both (Ax xA) otherwise one will stretch a bit more and then pull towards that side on drying; the thinner the boards the greater this stretch.
An A B laminate will pull towards the thinner board as will an A B A B and so on, whatever the number of layers.
I don't know how thick your finished boards will be but for real stability you can made an A B A laminate where B is 1/16 inch aluminum. I either shear the aluminum 1/4 inch smaller on each side and inlay it (my preference) or, if the same size as the boards (usually small books) edge the laminate with heavy bristol.
Best, James


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