Trade education and workforce development are two initiatives we value highly here at Dunn Lumber, so it should come as no surprise that we have close ties with Seattle Central College's Wood Technology Center (WTC). With roots dating back to the early 1900s, WTC's history intersects with ours at Dunn Lumber at various points (our very own Ed Dunn Jr. took some classes at Edison), and we're proud to be connected with such an exemplary educational institution.

Throughout the episodes in this series, we'll be speaking with Dave Borgatti, a long-time faculty member at the WTC, about the center's history, program offering, and various topics in woodworking education. Dave got his start in woodworking as a boat builder in Portland, Oregon, for Schooner Creek Boat Works, and ended up at WTC as an instructor in 1992. Since then, Dave has helped countless students—from boat builders to carpenters and cabinetmakers—learn the woodworking craft.

In today’s video, which is part one of two, Dave and I begin discussing how biscuit joiners work and how they are used. Watch the video above or keep reading for a detailed recap.

What is a biscuit joiner?

A biscuit joiner (sometimes called a plate joiner) is used to join various materials by making a spline joint. Most biscuits are small football shaped pieces of wood which correspond to the width and depth of the blade used to cut the kerf with a tool that resembles an angle grinder. Builders use these machines to create flush, even joints rapidly and reliably.

The tool and method of joining was created in the mid-1950s in Switzerland and originally called the Lamello Joining System (the word “lamel” stems from a Latin word meaning “a thin plate”). Today, the company Lamello is still well-known for making biscuit joiners and biscuits, as well as other systems, but other brands also offer biscuit joiners. 

Biscuit joiners have a small circular saw blade that cuts crescent-shaped notches in the opposite edges of two pieces of wood or wood composite panels. You can adjust the depth that the blade cuts into the wood to fit different biscuit sizes. 

How to use a biscuit joiner

Once the machine cuts a 5/32” kerf into both sides of a wood joint, glue is brushed into the slot and oval shaped pieces of compressed beechwood (the splines) are inserted into one side of the joint. Clamps are used to keep the pieces from shifting, and when the glue cures the joint will not move again. Note that beechwood tends to swell with moisture, so store your biscuits in a dry place, otherwise they won't fit.

Most builders use waterborne adhesives, so you need to work quickly before the glue expands the biscuits or they may not fit into the slot. If you need more working time when assembling materials, use epoxy or polyurethane adhesives as they won’t cause the wooden biscuit to swell. Whether waterborne or not, be sure and let the glue cure completely before finishing the wood, or there will be slight dimples on the face of the joint as the glue continues to cure. 

Different types of biscuits

There are three common biscuit sizes:

  • #0: ⅝” x 1 ¾”
  • #10: ¾” x 2 ⅛”
  • #20: 1” x 2 ⅜”

You can find biscuits in other sizes such as a S6, which is almost 3½” long, to a tiny “sub-zero biscuit” and even a biscuit for face frames. Biscuits made from plastic are used for temporary clamping or joining other materials such as solid surface (Corian) materials. Plus, there are a host of metal and Ready-to-Assemble (RTA) biscuits that fit into the same slot as a #20 wooden biscuit. 

Common uses of biscuit joiners

There are many ways to join two pieces of wood, but certain joints work better with certain materials or projects. Biscuit joiners are used when surfaces need to be absolutely flush. Installing cabinets or putting the edge on a countertop is simple when there are biscuits installed side by side.  

Biscuit joints can serve as a handy way to simply keep your project in alignment as you’re working on it or to join together large pieces of wood. For example, if you’re working on trim for a 16-foot room, you can use 10-foot pieces of trim, cut a scarph (angled cut), and use biscuits to bridge the long joint. After the glue has cured you now have a much longer piece of moulding with an inconspicuous joint. 

What shouldn’t you use a biscuit joiner for?

When it comes to strength, there’s not really any type of joint you should avoid with these machines. From synthetic resin glues to epoxies to polyurethanes there are many options for a builder. Dave recommends using a waterborne, synthetic resin glue like Titebond 3 for most wood joints. The wet glue expands the biscuit in the joint making it incredibly strong.

Ready to learn more? Check back here for part two of our discussion when Dave walks us through a step-by-step demonstration of how to use a biscuit joiner. Our Wood Technology Series covers everything from breaking down the pros, cons, and different uses of different types of wood, like ApplePly® to how to use various tools, like track saws, to get high-quality results. Here's a link to where you can find other episodes from our Wood Technology Series.