Biscuit joinery has been a topic of debate for years. Some craftsmen look down on it as if using them is almost cheating. It doesn’t have the look of a dovetail joint and is very simple compared to them. On the other hand there are individuals who wholeheartedly support using them when the project calls for it. Some joints need to be hidden and others aren’t visible in the first place. However, like all joints it has its shortcomings and strong suits.
Problems with biscuit joinery general derive from misuse or poor application of the technique. Some of these include exposed biscuits, misaligned surfaces, unsquare slots and glue line depressions. In addition to this, other techniques may offer advantages over biscuit joinery such as strength and accuracy.
What is a Biscuit Joint?
Biscuit joinery is a process used to join two pieces of wood together. It was created in 1956 by Hermann Steiner in Liestal, Switzerland. Steiner was working as a carpenter in the 50’s and was looking for a simple way to join particle boards. His solution was the biscuit joint and it has been used ever since.
A biscuit joint is composed of two slots and a biscuit. The biscuit is an oval shaped, compressed, and dried piece of wood. Generally biscuits are made from one of two woods, beechwood or birch. Biscuits come in a multitude of different sizes, but three are more common than the rest. These sizes are No. 0, No. 10, and No. 20 with each size meant for different applications. This biscuit is placed in the slots with glue as they are brought together and this creates a joint. They can be used in a variety of scenarios from simply joining to flat faces to creating corners with faces meeting at different angles.
Before I begin it is worth noting that an entire article could be devoted to the proper use of and different applications of biscuit joints. The small variations and different techniques for each situation are numerous and each craftsmen has his own approach. However, the basic idea will be the same for most projects. To begin you need a joiner. A joiner is the saw that cuts out the circular slots that the biscuit will slide into. In addition to this, you will need glue and an appropriate sized biscuit for the job at hand. Once you have all of this you can start working on the project.
Start by lining up the pieces that you will be joining. Using a pencil make a light line across the two boards at each spot you intend to put a biscuit. This distance varies based on the size of the wood and load requirements. In general, this will hover around twelve inch increments. After you have marked all your biscuit positions you will start cutting slots with the joiner. Set the joiner so that the biscuit can be fully inserted, but not past this point.
After the slots have been cut you will need to start gluing. It is important to use water based glue when working with biscuits. Using glue without water will fail to expand the biscuit and the joint will not be as strong. This will most likely cause the joint fail. Fill each slot about ¼ of the way full with glue and run glue along one face of the joint. Then push the two sides together and line them up. Finally, clamp the pieces of wood together and wait for them to dry. It is important to wait until the glue has fully set before moving forward.
Why Use Biscuit Joinery?
Biscuit joints have an assortment of advantages. Generally the first advantage one notices when using biscuit joints is the ease and speed at which they can be used. As I mentioned above the process is simple and involves little measuring. The ease comes from the inaccuracy in the slots allowed due to the slop and the three step process. The biscuit is smaller than slots which allows the user to adjust the joint after cutting and gluing. This is in contrast to other joints, such as a dowel joint that require precise measuring and cutting. Even if the dowel holes are only misaligned by a 16th of an inch the edge will be out of square.
In addition to this, the joint is relatively strong. The joint can be used for many light to medium duty applications such as drawers, boxes, and small cabinet work. Finally, like other hidden joints the finish is smooth and clean. This is quiet desirable in some styles and looks great.
Problems You Are Likely To Encounter
Biscuit joints, like all other joints, do have some downfalls and aren’t always the best answer for the project at hand. First, the goal of a hidden joint is for it to be, hidden. However, biscuit joints are prone to exposure when misused. Using biscuit joints when working with ¼ in. or thinner wood is generally not advisable. The biscuits can easily become exposed after very little sanding. It is also important to measure the distance from the edge of the biscuit to the edge of the wood if you are planning on routeing the edge or cutting from it. Cutting into and exposing a biscuit in this way can ruin an otherwise perfect project.
Along the same lines are exposed biscuit slots and glue line depressions. When joining wood at angles it is important to measure the slot depth. If the slot depth is set too deep the blade can protrude out the other side of the wood. To prevent this make a test cut on some scrap wood prior to cutting the biscuit slots on your project.
Glue line depressions are small divots in the wood where biscuits have been inserted. This is due to sanding or planing too quickly after gluing biscuit joints. While the glue is moist the surrounding wood and the biscuit expand. If one were to plane the wood while the wood is expanded it would then be a divot when the wood contracts. Preventing this is easier said than done, just wait until the wood and glue is sufficiently set. Although we all want to keep working on our projects its not worth ruining it to get a few hours ahead.
The next set of problems is derived from misalignment issues. Although, the slop in biscuit joints generally prevents misalignment issues they can still come up from time to time and if you are not aware of some of the common causes they can be quiet aggravating.
The first potential cause of misalignment is due to motor lurch. Biscuit joiner cutters are powerful machines with powerful motors and they have some lurching upon start-up due to the motors torque. When a craftsmen starts the joiner with the blade against the wood then the jolt from the motor can cause the slot to be angled. This is not a problem as long as both of the slots are at the exact same angle. However, if they are not the mating surfaces will be uneven. To prevent this simply start the blade prior to making contact with any wood. Misaligned mating surfaces occur when one piece of wood is lower or higher than the other. This is due to inaccuracies when using the joiner. To prevent these inaccuracies make sure to cut all wood from the same point of reference, the top or bottom of the wood.
Limitations of Biscuit Joinery
Biscuit joints, while good, have some limitations. These limitations come in both cost and strength. A nice joiner is an investment that will last for many years. However, it is an investment that exceeds that required of other joint types. For example, to use dowel joints one simply needs a drill, which most of us have long before a joiner, and a dowel jig. This extra cost is just not in the cards for some craftsmen and most will not be limited by their inability to use biscuits. The only real cost is in time spent working on dowel joints.
In addition to this cost limitation, there is also the issue of strength. A biscuit joint is far weaker than many other joints. The biscuit itself does not offer much in rigidity leaving the vast majority of the load bearing responsibilities on the glue. While this would be an issue if you were making a set of chairs, it would not be a problem for picture frames, or cabinet doors.
Strengths of Biscuit Joinery
Biscuit joints excel in a few common situations. First, when using particle board or plywood biscuit joints work very well. The joint is strong enough to handle the loads commonly associated with these woods. These could include, as I have mentioned before drawers or cabinet casings. The next big strength of biscuit joinery is the speed. Each joint requires two cuts and these cuts don’t have to be perfectly lined up. Dovetails require precision and multiple cuts for each joint. Although they are beautiful speed is not there strong suit.
Finally, they are exceedingly simple and easy to use. For the beginning woodworker using biscuit joints can allow them to have the satisfaction of completing projects. Developing the skill required to do other joints and work in different styles is important, but cutting dovetails or practicing lining up dowel joints isn’t going to offer the same satisfaction as finishing a project.
Biscuit joints are one of many different ways to join two pieces of wood together. They are simple, fast, and allow for some degree of inaccuracy. Biscuit joints offer a strong joint that will excel in many scenarios. However, they are not perfect solutions to every situation. Biscuit joints don’t offer the beauty or strength of other joints. If done improperly they can present a variety of problems that are just as difficult to deal with as other joinery methods. The biscuit joint has humble beginnings in Switzerland yet it remains relevant today, over 70 years after their inception. When working with any joint it is important to evaluate your needs and priorities prior to working. In some cases biscuit joints will be the best solution and in others it will not.
Article At a Glance
- Biscuit joints were created in 1956 in Liestal, Switzerland.
- Biscuit joints are used to join two pieces of wood with glue, a joiner, and small wood ovals called biscuits.
- Strength is not a trademark of biscuit joints; however, they are appropriate for many applications.
- Biscuit joints are fast and relatively simple to use.
- Many problems associated with biscuit joints are from user error. These include misaligned joints, exposed biscuits, and glue line depressions.
- Biscuit joints are great for picture frames, drawers, and other light load jobs.