Biscuits Beyond the Basics

Biscuit joinery was invented in 1955, and it still offers one of the best compromises between classic workmanship and strong, speedy results. Biscuits are used by some of the world’s most discerning craftsmen for another reason, too. They’re exceptionally versatile. You can accomplish much more with biscuits than first meets the eye. In fact, there are some jobs that only biscuits can do well.

Few people realize that biscuits are strong enough to join the stiles and rails of raised panel doors. It’s a challenging application, but #20 biscuits are up to the job as long as you install them differently than usual.

The stiles and rails on typical cabinet doors are best made with two biscuits per joint, each biscuit separated by about 1/8” of wood. Doors less than 12” high work fine with just one biscuit in each corner, though once you begin work you’ll run into something that’s puzzling.

The length of slots required for #20 biscuits is too long for all but the widest stile and rail joints. The solution is to cut biscuit slots off centre, so the extra biscuit length extends beyond the outside edges of the door. Saw the excess biscuits off, then sand them flush when the glue has dried.

It’s hard to believe, but biscuits are also strong enough to replace dados for joining the sides and shelves of even the largest wardrobes and entertainment centres. Install as many biscuits as you can safely fit in a single line across the width of your largest case goods. Swab glue into the slots and on the biscuits, assemble with clamps, then let dry.

Biscuits also offer a superb way to speed up door and window trim installation while also guaranteeing drum-tight corner joints forever. Instead of fastening the side, bottom and top trim pieces to the wall one at a time, pre-join them into a frame first using a single #20 biscuit in each corner. This is easiest to do when your molding design begins with flat sections of solid wood or veneered ply. Build the trim frame, finish it, then fasten it to the wall before adding additional pieces of mitred trim on the inside and outside edges.

Are you pre-joining door trim? Temporarily tack a piece of scrap wood as a brace across the back face of the open, bottom side of the trim frame during assembly and finishing. Remove the brace just before fastening the frame to the wall.

Have you ever tried to use biscuits to connect the corners of a mitred frame? The process isn’t likely to work well if your wood has an intricate profile. Any front-to-back mismatch of mating biscuit slots throws the parts out of alignment as they come together. And since the surface of the wood has a milled profile, you can’t sand the joint flush.

Instead, bring the mitre joint together with glue and clamps, wait for it to dry, then flip the joint over. Plunge biscuit slots across the hidden, back face of the joint, glue the biscuits in place, then saw and sand them flush afterwards. You’ll end up with a strong, perfectly aligned joint that’s just one of the many innovative ways your can use a biscuit joiner. No wonder they’ve become such a popular workshop joinery tool.