High speed automatic plywood calibrating sander line

this process is used to promise the board surface smoothly and the thickness in high precision. most of factory also
adopt automatic working line, but there are some different model. the sanding machine also have different model,
single face sanding and double face sanding. double face sanding have an high efficiency, the board go through one
time and both of the two side will be sanded, but this model price is much higher than single face. so factory prefer to use an automatic line with single face sanding machine.