Two methods to ensure square clamp-ups
To demonstrate the techniques involved in carcase clamping, we assembled a typical base cabinet. (This cabinet will later get a face frame, but our demonstration will not include that step.) You can adapt many of the techniques you see here for clamping boxes of all sizes: jewelry boxes, wall cabinets, and drawers, for example.
When you build a plywood cabinet, be certain to gauge the width of the rabbets and dadoes from the actual thickness of the stock, not its "nominal" or advertised size. Strive for dadoes that let you assemble the cabinet without hammering on the plywood.
Dry-clamp the assembly to check the fit of all the pieces, and to prepare your clamps. Make a pair of clamping cauls as shown in the drawing for each fixed shelf in the cabinet. These cauls will help distribute clamping pressure evenly over the length of the dadoes holding these shelves.
Apply glue to mating surfaces and clamp up the assembly as shown in middle photo. Check for square with a framing square, and double-check by measuring diagonally in both directions across the front of the carcase. If the diagonals aren't equal, place a clamp on the corners of the longer diagonal and apply pressure to equalize the diagonals. Leave all clamps in place for at least one hour, then unclamp. Install the back immediately to avoid straining the joints.
You can reinforce the joints with glue blocks positioned inconspicuously as shown in bottom photo. These blocks are easy to make, install quickly, and add strength to the cabinet's joints.
For more in-depth information on gluing and clamping, visit our Gluing and Clamping section in the WOOD Store.