12 ways to get the best from your biscuit joiner

For quick, reliable alignment and joining of project parts, nothing beats a biscuit joiner. At its most basic, you simply cut slots in mating pieces, add glue, insert a biscuit, and clamp. These 12 tips help your machine work harder.

Wondering which size biscuit best suits your project parts? Make this simple gauge to show the width of #0, #10, or #20 biscuits and the slots that hold them. Simply mill a slot for each size, glue in a biscuit—making sure you push it in only halfway—and mark a centerline for each. Then line up the centerline on your gauge with the layout line on your workpiece for a quick reference on which to use. (Use the largest biscuit possible for maximum strength.)

A few biscuit-joiner fences tilt to 135° to capture the end of a mitered workpiece. That keeps the tool stable when cutting the slot. If your joiner's fence maxes out at 90°, you can get the same stability with this trick. Simply clamp your mating mitered workpieces back-to-back so the bevels form a 90° angle, as shown, and cut slots on each miter.

The slot for a #0 biscuit measures about 2¹⁄₈ " wide, so you can't hide a biscuit joint in stock narrower than this. If you're making face frames—which are typically narrower than that—you won't be able to join them with any of the three standard biscuits. Here's a way to reinforce a joint with full-size biscuits on the back side—provided they won't be seen. Glue and clamp the mating boards together. When dry, cut slots across the joint line no deeper than ²⁄₃ the boards' thickness, and then glue in biscuits (top photo). After the glue dries, cut the biscuits off and sand them flush.

If you make a lot of narrow face frames, consider purchasing Porter-Cable's biscuit joiner, which includes an extra blade to cut smaller face-frame slots for special 1 ¹⁄₄ "-long biscuits.

Even a well-tuned biscuit joiner can sometimes cut slots that result in a non-flush-fitting joint. To avoid this, elevate the biscuit joiner with a sheet of sandpaper before cutting the face-grain slot. Then, after assembly, use your router to flush-trim the end grain of that piece for a perfect flush fit.

As with any cutting tool, a poor blade results in subpar cut quality. If you're seeing tear-out or hanging strands at the right-hand (exit) side of the slot, consider replacing the factory-supplied blade with a quality aftermarket one. We recommend Freud's six-tooth biscuit-joiner blade because its carbide teeth cut cleanly and last longer than the teeth on most stock blades.

If you live in a humid climate, you know how biscuits can swell—sometimes even despite storing them in sealed containers—resulting in biscuits that won't fit in the slots. That's a problem when your glue begins to set up and you've got a lot of biscuits to install. Sure, you can shrink biscuits in a microwave oven, but they'll likely come out different thicknesses. So run your biscuits through the Biscuit Press, an aluminum hand-cranked tool that compresses them to uniform thickness.

Referencing biscuit slots using the machine's base rather than the fence usually works great, provided your workpieces sit perfectly flat against the benchtop. Because it takes both hands to operate the joiner, you need a helping hand to secure the workpiece. Kreg's Bench Klamp System provides quick clamping, particularly with slightly bowed stock. To install this clamp, rout a recess into your benchtop and mount the flush-fitting plate with screws. When not in use, remove the clamp via the keyhole slot in the plate.

Sometimes, cutting slots into workpiece edges can be tricky because the short fence fails to provide enough reference surface to prevent tipping. That's when you need this base extension. Build it from plywood or any scrap stock that's flat.

If you're cutting multiple biscuit slots in wide side panels, such as for shelves in a bookcase or cabinet, make a T-square for repeatable accuracy. Glue and screw the parts together at exactly 90°. After the glue dries, mark biscuit centerlines on the arm. Now use the T-square to line up your biscuit joiner for cutting slots in the case sides and mating shelves, referencing the T-square from the same edges.

If you do a lot of biscuit joinery, you'll appreciate this versatile jig, with fences and guides that make cutting slots easy and accurate, including on beveled and mitered workpieces. Build it according to the plan in issue 161 (February/March 2005) or download it for free at woodmagazine.com/biscuitjig. Mount your biscuit joiner in the jig, clamp the jig to your workbench, and you have a rock-solid workstation.

Splines add both strength and visual appeal to normally weak miter joints, especially when you make the spline from a contrasting wood species. Cutting the spline slots on your tablesaw requires a tall jig, but you can cut them easily and quickly with your biscuit joiner and the attached fence jig, see drawing below.

Here's how to do it. First, assemble your mitered project and allow the glue to dry. Cut two mirror-image triangles, as shown, mounting them to your joiner's fence with machine screws and nuts. Set your joiner's cutting depth as deep as you can. Trap the mitered corner in the fence jig and plunge a cut centered on the workpiece's thickness. Then glue in the spline of your choice. When dry, trim it and sand flush.

To use "Z-clip" fasteners to secure tops to tables, desks, and dressers, you typically saw a blade kerf along the rails or aprons. To avoid any potential weakening that might result from the full-length kerf, use your biscuit joiner to cut slots where the fasteners will mount. Set the joiner for the No. 10 depth slot, adjust the fence to cut the proper distance from the top of the rail (usually ¹⁄₂ "), and plunge the blade. You can do this before or after assembly.