When it comes to assembling sheet goods, nothing is quite as fast and efficient as a biscuit joiner.
The biscuit joiner was initially developed in the late 1950s by Herman Steiner. The Swiss cabinetmaker was looking for a better method to assemble the cabinets he was making from the newly introduced particle board. Because of the way particleboard was manufactured, the joinery techniques in use at the time with solid wood panels were not suitable for this new material. Steiner introduced the first portable plate joiner, under the name Lamello, in 1968. The patent protection for the Lamello has long since expired and now many different manufacturers offer biscuit joiners as part of their woodworking tool line.
A biscuit joiner (or plate joiner) is designed to aid in the assembly of man-made panels in cabinet carcass construction. The body of the tool is essentially the same as that of a portable angle grinder. Instead of spinning a grinding wheel it spins a small 4” saw blade with carbide tipped teeth. Using a fence on the front of the tool, the tool is registered against the work piece and the blade is plunged into the material to make a crescent shaped groove. A matching groove is then also cut in the opposing piece. Glue is applied to the grooves, an oval shaped ‘biscuit’ (plate) is inserted into the groove, and the two pieces are clamped together. As the biscuit absorbs moisture it expands slightly to fill the grove. This method of joinery has simplified countless tasks, from cabinetry and window casings to rail and stile doors, face frames and furniture.
The wooden biscuits that serve to connect two pieces of sheet goods together are all 4mm (5⁄32”) thick, and come in three standard sizes: #0, #10 and #20. These are made from a hardwood, often beech, which has been dried and then compressed in a press. When in contact with glue the biscuits absorbs the water to expand slightly and fill the space in the biscuit groove. Since all manufacturers use the same size blade to cut the biscuit grooves, biscuits are interchangeable from model to model; what will differentiate one biscuit joiner from another is the fence. However, not all biscuits are alike. Some brands seem to have a lot of variation in biscuit thickness; sometimes the biscuits are difficult to insert in the grooves, and at other times they are too loose. Ideally you want a biscuit that fits inside the groove snugly. It’s a good idea to keep your biscuits sealed in a plastic bag or container when not in use.
The Porter Cable 557 joiner includes a 2” blade (in addition to the standard 4” blade) to cut grooves for a ‘mini’ biscuit (#FF), which measures 13mm x 30mm (½” x 1 13⁄64”). These are particularly useful for assembling very small boxes, face frames and moulding.
When joining two panels it is critical that the biscuit grooves be cut perfectly parallel to the fence for the panels to line up with each other. To cut these slots accurately a biscuit joiner must have a solid main fence that moves smoothly through its plunge cycle without any resistance or hindrance. When the plunge mechanisms are built to lower tolerances, any slop in the travel will lead to the fence racking as it is plunged, resulting in erratic travel. When looking at the fence, pay particular attention to the adjustment knobs. The main fence should be easy to adjust through its various settings and when positioned, the settings should be firm enough to remain in place, without drifting, through a day’s work. They should be easy to access and be simple to manipulate, with sufficient heft to allow them to be tightened without breaking off or stripping out.
The biscuit joiner must be able to cut a slot parallel to a board’s edge at varying thicknesses, and to do this it uses a height adjustment fence that drops down from above and is locked in at a chosen angle or by registering both the biscuit joiner and the pieces to be joined off the same flat work surface. Any play in the fence mechanism that allows the blade to wobble on its axis will result in a slot that is too wide for the biscuit. This could also be caused by excessive run-out on the saw’s arbour as well. If the slot is slanted from one side to another then, when the two sides are brought together, the two halves will slope in the opposite direction with the end result that the biscuit may not fit. Some models, like the Triton TC9BJM (tritonwoodworking.com) have a main fence with a removable, height adjustment fence; on the Triton this fence is adjustable in height from 0” to 1 ⅜”. On other routers the adjustment fence is integrated into the main fence.
The three different size biscuits (#0, 10 and 20) require different depths of cut, which is set by the depth adjustment knob. The letter ‘M’ stands for maximum depth capacity of the tool. The adjustable fence can be easily angled to cut slots on a bevelled edge. On the front of the main fence is a cutting guide line that is lined up against the cutting line on the work piece. A set of anti-slip grips on the front of the main fence help to keep the biscuit joiner steady on the work piece. On some biscuit joiners the handle is attached to the main body of the unit; on other joiners the handle is attached to the main fence.
When it comes to dust extraction for biscuit joiners there are three options. You can let the debris be ejected from the machine onto the floor, you can capture it in a bag, or you can connect it to a powered dust extractor. When working on a few joints, or if you happen to be in tight quarters, then it is not too much of an issue to simply let the debris fly. Cutting the small slot doesn’t produce a lot of waste. If you are working at a bench and will be cutting a lot of slots, connecting a dust collection bag to the dust port is a good idea. It will keep your work area clean and the air clear. If you will be using your machine a great deal, connect it to a dust extractor that switches on automatically when you use the biscuit joiner.
The carbide tipped blades that come with these tools should remain sharp for a very long time. When it comes time to change the blade, some of these tools provide easy access for this; others make it somewhat more of a chore. You can likely get a couple of sharpenings out of the blade before you have to purchase a new one.
Contrary to popular belief, biscuits are not meant to keep bowed panels aligned when gluing up panels. Using biscuits to compensate for poorly prepared stock is a poor construction practice, as the panel will continue to have internal stresses because the stock was not prepared properly before the glue was applied. Seasonal movement of the wood will compound these stresses. Ensure your boards are straight and true before gluing them up.
Biscuit joiners were developed to provide a simple, cost effective method for cabinet shops to join particleboard panels. If that was all they were used for, they would be of little interest to the average woodworker. Fortunately these tools are much more versatile. They are commonly used when assembling kitchen cabinets and other case goods, window casings and other architectural trim. Biscuits are also used in the construction of rail and stile doors, bookshelves, drawers and when making and installing face frames on cabinets.
If you only work with solid wood, a biscuit joiner might still be of interest. When assembling a large panel from narrower boards it can be a benefit to use some biscuits to help align the boards and keep them from sliding relative to each other as you tighten the clamps. For simple projects, biscuit joinery will suffice in all but the most demanding applications.
If you don’t find yourself building a lot of kitchens and your biscuit joiner is gathering dust, you may prefer to look to one of its alternate uses. I use my biscuit joiner to reinforce the mitre corners on small boxes and picture frames (see Biscuit Mitre Jig). The biscuit joiner is a fantastic tool to add splines to any glued mitre joint. Splines strengthen this notoriously weak end grain glue joint by providing additional face grain glue surface. When contrasting woods are used it provides a decorative corner element. Spacing them up the side of a box gives a decorative joint that looks similar to a finger joint.
A biscuit may not be a suitable substitute for more traditional joinery in some situations as it is typically the weakest joint when compared to mortise and tenon or dovetail, but it certainly has a home in any well equipped workshop.