Plate Joiners for a Perfect Fit

Once found almost exclusively in cabinet shops, plate joiners (sometimes called biscuit joiners) have become increasingly common in home workshops and on construction sites, and for good reason: they make the process of joining two boards together fast, simple, and safe.

Useful for making butt joints, miter joints, and edge-to-edge joints, plate joinery can be used with just about any type of wood, as well as with materials ranging from particle board to solid-surface countertops. With a plate joiner, you can quickly make bookshelves and cabinets, reinforce many of the joints made by trim carpenters, or invent entirely new applications.

How Does It Work?
Plate joiners are relatively small, barrel-shaped tools that take up less room in the toolbox than a circular saw. They are designed to do only one thing: cut crescent-shaped slots of various sizes. But plate joinery is actually a two-part process. Once you've made slots in the two pieces to be joined, the second step is to put glue in the slots and insert biscuits into the mated pieces.

Biscuits are wafers made of compressed beech chips stamped into a football shape, sized slightly smaller than the slots that the joiner cuts. This leaves a little bit of play so that joints can be more easily aligned (try that with a doweled or mortise-and-tenon joint!) and provides room for the glue. Once the glue comes in contact with the biscuits, they absorb moisture and begin to swell. This is what makes biscuit joints so tight and strong.

The Mechanics
Plate joiners use a 4-inch-diameter carbide-tipped circular saw blade that usually has six teeth (though some blades have 10 or more). The blade is mounted so that most of the time it's safely out of harm's way behind the joiner's spring-loaded faceplate. When you press the faceplate against a workpiece, the blade extends through a slot in the faceplate, cutting a kerf (notch) of predetermined depth into the wood. The fence helps guide the position of the kerf, while the depth of the cut is controlled by a quick-set stop mechanism.

Biscuit Fits
All plate joiners have at least three preset cutting depths that correspond with the three basic biscuit sizes. In addition, some joiners have presets for various specialty biscuits, knockdown fittings, and hinges. And some plate joiners come with (or can be fitted with) a small, 2-inch-diameter blade for cutting the small slots needed by the new breeds of smaller biscuits.

The three basic biscuit sizes are:

• #0: About 5/8 of an inch wide by 1 3/4 inches long (47 x 15 mm)
• #10: About 3/4 of an inch wide by 2 1/8 inches long (53 x 19 mm)
• #20: 1 inch wide by 2 1/2 inches long (56 x 23 mm)

There are also smaller face frame or mini biscuits that are designed for use with materials as narrow as 1 1/2 inches, such as cabinet face frames.

Questions Before You Buy
How well your plate joiner will work for you depends on a few factors:

How much power does the motor pack? Plate joiners typically range in power from about 4.5 amps to 8 amps. Higher amperage is particularly important if you do a lot of cutting in hard woods.

Bushings or bearings? Both durability and accuracy are affected by whether the joiner uses bushings (which can result in more end-play in the spindle) or bearings (which are preferable).

What kind of fence system does it use? Probably more important than sheer power is a joiner's fence system. The best fences are accurate and easily adjustable, allowing the user to make different kinds of cuts without going through a long setup procedure. Fences that have fixed stops at 45 and 90 degrees are less versatile than those that can be adjusted to any angle within that range. On some joiners, the fence has to be removed to make a flush cut. Some require a special tool to change the fence's position on the faceplate; other joiners are equipped with a knob for easy fence adjustments.

Are the handles adjustable? Ergonomics counts with plate joiners, too. Look for adjustable handles, which make it easier to change gripping positions.

What about sawdust? Plate joiners generate a considerable amount of sawdust. To avoid this health hazard, you'll want some sort of dust collection capability. Many joiners come equipped with a dust collection bag or have a port that can be connected to a vacuum system.

Any storage advice? If possible, choose a joiner that comes with a case so that you can keep the tool, its accessories, and the different biscuits you'll need all in one place.

The Cost of Joining
Plate joiners range in price from less than $150 to almost $1,000 for a top-of-the-line "showpiece" tool. A cabinet shop that uses the tool day in and day out might require the precision and durability of a premium-priced machine. The good news is that most carpenters and do-it-yourselfers will be happy with the wide selection of lower-cost plate joiners that have plenty of features and are a good value.

Andrew Wormer is a contributing editor to Fine Homebuilding magazine and the author of The Builder's Book of Bathrooms and The Bathroom Idea Book.