A New Manual for Biscuit Joiners

Use a biscuit to help set the depth of cut. Insert it in a slot and mark a pencil line at the intersection of the plate and the edge of the material.

Use a biscuit to help set the depth of cut. Insert it in a slot and mark a pencil line at the intersection of the plate and the edge of the material.

The biscuit joiner is one of those tools that promises to make life so much easier. The ability to make relatively strong joints quickly and easily makes this a tool you really must have. Yet many woodworkers find it frustrating; for some reason the joints never quite line up and in the end it doesn’t seem to save that much time.

It isn’t the fault of the tool. The truth is that most woodworkers don’t know the right techniques to make the most of their biscuit joiners, and there are some common attitudes and assumptions that hurt more than help, and don’t speed things up.

Some joints in woodworking are for show and some are for utility. Biscuit joints won’t make your friends and family ooh and aah over your skills, but they will help you locate and connect parts without much fuss so you can get on to more important things.

Adjust the depth setting on the tool so the gap between the two lines is about  1/8". This will allow some room for glue within the joint and some lateral movement for fitting.

Adjust the depth setting on the tool so the gap between the two lines is about 1/8″. This will allow some room for glue within the joint and some lateral movement for fitting.

Fifty years ago, Swiss woodworker Hermann Steiner had a great idea and formed a company called Lamello to market the oval-shaped joining plates and the tools to cut the slots. I first saw one in 1981 when the German-born foreman of the cabinetshop I was working in brought out a new toy he called a cookie cutter.

We were all impressed with what it could do, and every one of us wanted one of our own. What stopped us in our tracks was the $600 price of the machine. The Lamello model is undoubtedly the best in the field. It’s made like, well, a Swiss watch.

The Lamello is still the highest-priced machine in the category, selling for four to five times the price of other machines. In a production environment the investment is worthwhile, but if you’re not using it on a daily basis, the lower-priced models will likely meet your needs. But if you drive to the tool store in a Mercedes or BMW, you won’t regret buying the Lamello.

Make the Machine Perform

The most common mistake is allowing the machine to tilt as you cut the slot, preventing the parts from lining up properly.

The most common mistake is allowing the machine to tilt as you cut the slot, preventing the parts from lining up properly.To make the average biscuit joiner perform at its peak, there are a few things to check and possibly adjust.

First you want to minimize any sloppiness in the tool’s plunge mechanism.Every model is a little different, but generally you want to check that all the screws are tight and the motor slides freely on the base. Spraying a dry lubricant on the tool’s ways will help. Check the fence. It too should move freely; the stop may need to be adjusted to 90°.The last adjustment to make is to set the depth stop. This is done by making a test cut for a #20 biscuit, with the tool on the correct setting. You want the resulting cut to be a bit beyond half the width of the wooden plate. This allows the two parts to join snugly while giving you a bit of room for lateral adjustment during assembly. Make a cut in some scrap, put a plate in the slot, then draw a pencil line where the plate meets the edge of the slot, as seen in the photos at right. Then turn the plate around, reinsert it, and draw a second pencil line. When the gap between the two lines is between 3?32″ and 1/8″, you have the depth setting adjusted correctly.

The Nut Behind the Wheel
Don’t worry about centering the slot on the thickness of the material. Set the fence so that the slots will register from the base of the tool.With the machine ready to go, it’s time to make sure you understand how the tool works and what it’s good for. In some applications it’s ideal, but it’s not a panacea. If you’re joining two pieces of solid wood edge to edge to make a panel, the main benefit of the biscuit is to align the parts. The joint is strong enough as it is, and adding biscuits may introduce additional problems as well as make extra work.

Turning a corner is a different story; with biscuits, you can make a simple butt joint in a case or box into a much stronger joint. You also get the benefit of having the parts line up at assembly – if your technique is sound.Using biscuits in miter joints can be an iffy proposition. Biscuits work well if you have the machine perfectly aligned when you make the slots. If you’re off by even a tiny amount however, the error will be doubled, and you’ll likely do more harm than good.Problems arise if you don’t hold the work steady and you don’t keep the tool flat. This simple jig will let you keep both hands on the tool and the workpiece from moving.

In any type of joint, small errors in aligning the tool to the work as you set it in place, and as you make the cut, account for nearly all the problems you may encounter (as seen in the photos below). It’s common to think that the machine is so easy to use that you can’t go wrong, but like any other joint, the care you take setting it up and cutting it make all the difference.

Two Total Time Wasters
People tend to concentrate on two things that don’t matter and then ignore the most important part of the process. Centering the tool’s cutter in the thickness of the material isn’t necessary. You’re far better off to set the fence by placing the tool on a flat surface, putting a piece of the material you plan to use next to it, and lowering the fence until it touches the top face of the material, as shown in the photo below.

A guide block will locate the position of a shelf, and provide layout marks.

A guide block will locate the position of a shelf, and provide layout marks.

Now you have the tool set so that the cut is indexed both from the fence and from the base of the machine. That is far more important than having the slot centered. There is in fact a big advantage to having the slot offset; it ensures that the face you want to show won’t be hidden by accident.

It is also much easier to keep the machine flat by working from the base for as many cuts as you can. I only use the fence as a last resort. The jig  shown above right will hold the work flat for you and provide a flat surface for the base of the machine.

To make this jig, all you need is a flat piece of Medium-density Fiberboard (MDF) or plywood, a smaller piece screwed down to one corner, and a third piece below the front edge to act as a hook to your bench. Attach the jig firmly to your bench with a clamp or a few screws, and mount a hold-down toggle clamp as shown above.  This will hold your work safely, letting you keep both hands on the machine and it gives you a flat reference surface for the base of the tool.

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