In order to improve the nature of natural wood anisotropy, so that the plywood characteristics of uniform, stable shape, the general plywood in the structure must adhere to two basic principles: first, symmetry; the second is that the veneer fibers of the adjacent layer are perpendicular to each other. Symmetry principle is to require plywood symmetrical center plane on both sides of the veneer, regardless of wood properties, veneer thickness, layer number, fiber direction, water content, etc., should be symmetrical. In the same plywood, single tree species and thickness of veneer can be used, and single plates with different tree species and thicknesses may be used, but any two layers of symmetrical single plate trees and thicknesses on either side of the symmetrical center plane are the same. The surface backplane allows not the same tree species.
To make the plywood structure conform to the above two basic principles, it should be an odd number of layers. So the plywood is usually made of three layers, five layers, seven layers and so on odd layers. Plywood the name of each layer is: surface veneer called Table board, the inner veneer is called the core plate; The front table panel is called the plate, the back table plate is called the back plate, in the core board, the fiber direction is parallel with the table plate is called the long core board or the medium plate. When forming the slab, the panel and the back plate must be facing outwards.