How to finish and assemble CNC plywood furniture

The short answer: do a dry fit first, sand the parts, glue and clamp them square, and finish the piece last. Birch and similar plywood take a stain unevenly, so test the finish on an offcut, and ease every edge that people will touch.

Measure both diagonals: if they are equal, the piece is square.

Before you glue: the dry fit

Lay out all the parts and match them against the parts list in the assembly guide.
Remove tabs and sand the stubs flat. Break the sharp corners of the edges lightly.
Assemble the piece without glue. Joints should go together with hand pressure or a light tap with a mallet and a wood block. If you have to force them, stop and read the guide on plywood thickness.

Sanding

Sand the faces and edges with 120 to 180 grit paper, then 220 if you plan to stain or oil.
Sand before you assemble: inside corners are hard to reach afterwards.
Do not sand the faces of joints that have to fit. A small amount of sanding changes the thickness and the clearance.
Go gently on thin veneers, they sand through quickly.

Gluing and clamping

Use a wood glue, spread a thin film on each joint and avoid adding too much, because the squeeze-out stains bare wood.
Assemble, then check that the piece is square by measuring both diagonals. If they are equal, it is square.
Clamp with a few scrap blocks to protect the faces, and wipe the squeeze-out with a damp cloth before it dries.
Let the glue cure for the time on the label before you load the piece.

Finishing the edges and faces

Edges: the layers of plywood are part of the look. Sand them smooth and seal them with the same finish, or cover them with edge banding for a clean surface.
Birch and maple: a pre-stain conditioner reduces blotching if you stain.
Clear finishes: water-based polyurethane stays clear. Oil or hardwax oil gives a warmer, softer look and is easy to repair.
Painted pieces: prime, sand lightly and paint in thin coats.

Children's furniture and tall pieces

For pieces used by children, round the edges well, use a finish that is rated safe for toys and surfaces children touch, and fix tall pieces to the wall with the brackets in the guide. Find ideas in the children's furniture plans.

Frequently asked questions

Do I sand before or after assembly?

Before. Inside corners are hard to reach after gluing. Do a final light sanding after the glue has cured.

How do I check that the piece is square?

Measure both diagonals. If they are equal, the piece is square. Adjust the clamps before the glue sets.

How do I finish plywood edges?

Sand them smooth and seal them with the same finish as the faces, or cover them with edge banding if you want a clean surface.