How to Use a Biscuit Joiner for Strong Joints

A plate joiner, commonly called biscuit joiner, biscuit cutter, or biscuit jointer is a power tool used to make very strong joints in woodworking projects. Using a small football-shaped wafer of compressed wood called, not surprisingly, a "biscuit" to bridge the joint between two pieces of wood, these tools are fairly inexpensive and extremely easy to use. The wood joints produced with a biscuit joiner are very strong without the use of nails, screws or other mechanical means of attachment.

Primarily used to join the edges of boards together, as in a table top, they can also be used for joining the corners of drawers, picture frames, or many other types of joints commonly used in woodworking.

The biscuit joiner consists of an adjustable fence for proper placement and a small motorized "saw blade" that cuts a rounded hole into the pieces of wood being joined together. Glue is placed in the hole, the biscuit is inserted, and the joint then clamped until the glue sets. The moisture in the glue expands the compressed wood of the biscuit, making a very strong joint. One of the best things about using a biscuit cutter instead of dowels is that the biscuit joint has a small amount of adjustment possible; the holes need not exactly line up as they do when using dowels.

The most common use of a biscuit joiner is to join two boards together edge to edge, making a wider surface, and it is here that the biscuit joiner really shines. To accomplish this joint, lay the boards on a smooth surface in the orientation and position desired for the final assembly. Boards should be smooth, requiring only a light sanding before finishing, with the edges to be joined together as straight as possible.

Mark the locations of the biscuits on both boards. If many boards are to be joined, it is easiest to use a straight edge and mark them all at the same time with a light pencil line running across the entire surface. For ¾" lumber, a biscuit every 12" or so is adequate, while with 2X lumber a biscuit every 18" or so will do fine.

There are three sizes of biscuits to choose from; #0, #10 and #20. You should probably have a small supply of each size available, as most jobs will contain many different types of joints to be made. Choose a size of biscuit; a #20 is normally used for edge gluing. This is the largest of the biscuits available and will extend further into each board. Other types of joints may require smaller biscuits so that they don't protrude beyond the back surface of the board.

Set the fence so that the blade will project into the center of the board. It is not necessary to have the exact center, but get it as close as possible. With the side of the board with the line drawn on it facing up, position the biscuit joiner at the edge of the board, turn the tool on, and firmly push the blade into the wood. This will cut the slot that the biscuit will fit into.

Repeat for each line drawn on each board. Add glue to the slots cut for the biscuits, making sure that each slot is filled to about 1/4 of its depth with glue. The edge of one board of each joint should also have glue along its entire length. Insert the biscuits into all the slots cut into one board, centering them in the slots. Again, it is not necessary to get them into the exact center; just center them by eye and it will be good enough. Press the other board onto the biscuits and clamp the assembly until dry. If too many boards are to be joined together, it may be necessary to only glue a few at a time in order that the glue not set up too much while getting all of the boards together before clamping.

After the glue has dried, some sanding will likely be necessary to make the surfaces of the boards line up completely smooth, but it should be very minimal. The biscuit cutter, if used correctly, will cut the slots for the biscuits at precisely the right depth in each board. A few thousandths of an inch should be all that needs sanding off.

Joining the edge of one board to the face of another is another common joint in woodworking. Such joints might include joining the sides of a drawer to each other or joining a small shelf to the surface of the shelving side piece.

In the first photo below, two boards are to be joined at right angles. Position the boards as they will be in the finished product and again mark the locations of the biscuits. The slots in the edge of the board are cut the same as for edge gluing, while the slots in the vertical piece are cut while holding the board vertical. A 2X4 has been clamped to the workbench surface as a guide to hold the vertical board while using the biscuit joiner. Although not shown, a good idea is to place a piece of sandpaper under the biscuit joiner to very slightly raise the joiner; this is done so the the vertical piece will very slightly project past the horizontal piece. It is much easier to sand down the projection after gluing rather than sand the entire horizontal piece. This is also shown in the video above.

To cut the biscuit slots in the center of a larger board, as in the side of a shelving unit, position the two pieces where they are to go and mark both pieces. An additional mark needs to be made along the entire face of the shelving side board where the shelf will be placed, and a 2X4 or other thicker piece of lumber clamped there to provide a fence for the biscuit joiner to ride on. Use the joiner in the vertical position as shown to cut the slots, with the base of the joiner against the temporary fence - this will produce slots in the same relative position as the shelf itself. Alternatively, the board could be clamped into the workmate (if such a workbench is available) so that the line representing the bottom of the shelf lines up with the surface of the workbench. Either way the objective is to give something for the biscuit joiner to rest on.

Safety is always a concern - eye protection should always be used. The loss of an eye isn't worth a strong joint or quicker work - protect your eyes. Although a biscuit joiner is one of the safer power tools it is still dangerous. Never push the blade out unless you are actually cutting a slot. Never turn the tool on until ready to cut. A little common sense and safety consideration will go a long ways here.

A good, flat workbench is necessary when using a biscuit cutter; a wavy surface supporting either the cutter or the wood will result in slots that won't line up properly. The photos show the work being done on a Black and Decker Workmate bench, which can also be used for clamping during the gluing process, and is recommended for nearly any home workshop.

Sawn edges to be joined together must be straight and smooth. Make sure that any circular saw used is of decent quality and that the blade is sharp. Your home tool set will surely include some sandpaper by now for sanding edges, but clamps and other items may need to be chosen.

A biscuit joiner can be one of the handier tools for the woodworker; if you don't have one yet, look into buying one along with a few biscuits for your next home improvement project.