How plywood is made

Plywood starts as a log peeled like a roll of paper towels, then stacked with every layer's grain crosswise.

stations: 6
things upstream: 28
raw sources: 8
steps from the ground: 8

The short version

Plywood is made by spinning a log against a long blade, which peels it into thin sheets of wood veneer. The sheets are dried, graded, coated with glue and stacked so the grain of each layer runs at right angles to its neighbors. A hot press bakes the stack into a flat, strong panel that is trimmed and sanded.

Peel the log

A straight, wide log is laid horizontally and spun on its long axis while a blade presses into it. A continuous sheet of wood unrolls, the way paper comes off a roll. A bar presses on the log beside the blade to hold the sheet to an exact thickness.

Goes in
Timber
Clip and dry the sheets

The long ribbon of veneer is cut into sheets slightly bigger than the finished panel, because wood shrinks as it dries. Dryers then take out the water so the glue will bond properly.
Patch and sort the veneer

Workers grade the sheets and patch knot holes and splits. The best sheets are saved for the outer faces, and plainer ones go inside.
Glue and cross-stack

Glue is spread on each sheet and the layers are stacked with the grain turned 90 degrees from layer to layer. That alternation keeps nails from splitting the edges and stops the panel from swelling and shrinking much across its width. The number of layers is always odd. Indoor panels use a cheaper glue with limited water resistance, and outdoor and marine panels use a waterproof one.

Goes in
Adhesive
Bake in a hot press

The stack goes into a heated press that squeezes the layers together while the glue cures. The panel comes out as a single flat board.

at least 140 °C
Trim and sand

The panel is cut to its standard size, small surface flaws are filled, and sanders smooth both faces for the market it is headed to.

End of the linePlywood Next it goes into shipping container, drum kit, wooden door and 3 more.

Worth repeating

The British De Havilland Mosquito aircraft used plywood for its wing surfaces and was nicknamed the Wooden Wonder.
The standard 4 by 8 foot sheet traces to a veneer-core plywood developed for the 1905 Portland World Fair.
Howard Hughes's H-4 Hercules airplane was built of plywood and resin.