Plywood: Different Techniques for Different Jobs

Plywood can be mortised, dovetailed, mitred and worked similarly to solid wood in many ways. Provided it is thick enough. Avoid using plywood for drawer sides — the edge of ply is made up of edge grain, glue and end grain, which vary in hardness and wear unevenly, thus tending to cut the runners rather than slide.

Sawing

Cut 0.8-2 mm with a knife; for other thicknesses, use a fine-toothed saw — from 2-6 mm a dovetail or small tenon saw, from 6-12 mm a tenon saw; above that a panel saw. Always mark a cut line with a knife when cutting across the grain, and cut on both sides of the sheet to prevent any breakaway.

Pinning and screwing

Always drill pilot holes before screwing. Pins and screws do not hold as well in the edge of ply as they do in the face. When soft ply is being fixed with screws, there is a danger that the screw heads may sink too far into the veneer. Use screw cups to reduce this risk. The hold in birch ply is better than in Gaboon and Douglas fir.

Gluing

Always rough-up the surfaces of ply so that the glue will have something to grip. Use coarse glass-paper or a toothing plane.

Apply as much even pressure as possible while the glue is setting. For marine or outside work, use a waterproof adhesive. If you join sheets of ply, they will remain more stable if the joining faces have the same grain direction.

Jointing

Plywood over 9 mm thick can be jointed as ordinary timber. Joint edge-to-edge by the loose-tongue method, but do not bend the sheets after joining.

Leave gaps between tongue and groove bottoms.

Repairing

If small pieces of laminated veneer lift during work, glue and cramp them in place again, using softening and paper.

Protection

Wherever possible, fix ply so that its edges are supported. Sharp blows to the edge often cause delamination and tearing. Protect the edges with lipping where there is a danger that they may be knocked.

Alternatively, remove the sharp edge with a small chamfer.

Bending

The thinner the sheet, the more it will bend.

Birch is one of the best plys for bending.

 

Fairly simple, even curves will hold their shape if you bend two or more sheets of ply and glue them together, using temporary formers. Slight damping of what will be the outer curve of each sheet will help it to bend, but on no account glue the sheets together while they are still wet: let them dry out overnight in the new shape.

Ply will bend to a tighter curve when the grain is running across the curve than when it is running with it.

27. June 2011 by admin
Categories: Woodworking | Tags: , , , , , , | Comments Off on Plywood: Different Techniques for Different Jobs

Follow

Get every new post delivered to your Inbox

Join other followers: