One of the commonest techniques for a woodworker to learn is what we call “joinery.” It is nothing but the art of joining together two sections of wood. There are several types of woodworking joints and the biscuit joint is one of them.
Any guide to biscuit joints in woodworking will make them seem easy to mark out, cut, and execute. Biscuit joints are not as strong as many other types of joints. They may not withstand heavy loads or high impact. But many woodworkers, cabinet makers in particular use biscuit joints to assemble and align sections of wood together.
What is a Biscuit in Woodworking?
A biscuit is an oval or football-shaped thin wooden disc made from compressed wood, typically beech. The biscuit then is placed in the common slot of two corresponding sections of wood.
You fill the common slot with glue and then insert the biscuit. As it dries, the biscuit swells inside the slot due to moisture from the glue and secures the two sections of wood. We make biscuits with a biscuit cutter and they come in the following sizes:
- #0: 5/8 inch by 1 3/4 inches
- #10: 3/4 inch by 2 1/8 inches
- #20: 1 inch by 2 3/8 inches
Therefore, if you buy a biscuit cutter, ensure that it cuts these three sizes of biscuits.
We use a power tool called a biscuit jointer or plate cutter to cut the slots for biscuits. A biscuit jointer is a power tool that uses a small circular blade to create a semi-circular slot into which the biscuit fits. If done correctly, the joint created by a biscuit joiner creates a seamless joint.
What is a Biscuit Used For?
We use biscuit joints as an alternative to mortise and tenon joints. These joints are easier to make, are faster, and create an invisible joint in wood. Biscuits are an effective solution to join planks of wood that are placed end-to-end to each other.
We use biscuist to join sections of boxes, cabinets, drawers, face frames, miters, and edge banding. Various sizes of biscuits serve the purpose of joining wood of different thicknesses.
For example, we use a size 20 biscuit to join wood of 3/4” thickness and a 0-size biscuit for joining drawer and face frames and other thinner and narrower wooden sections.
Common Types of Biscuit Joints
It may come as a surprise to many that there is more than one type of biscuit joint. There are several types of biscuit joints depending on the orientation and thickness of the wooden sections being joined. Here are some of the commonest types:
Edge Grain to Edge Grain
This is the commonest type of biscuit joint. It makes the edge grain of two different planks of wood. A good example is joining flat sections of wood for a tabletop. We use a biscuit jointer to cut the slots of equal dimensions.
Then, the biscuits are inserted with glue and the sections are pressed together, end-to-end. The advantage of this type of joint over a tenon or dowel joint is that you get some allowance to adjust the joint laterally.
You can make excellent miter joints with a biscuit jointer as you can get excellent slots between two mitered pieces. The advantage is that this joint offers enhanced surface area for holding the glue as compared to a standard mitered joint.
You can create such joints for door and window casings and picture frames. These joints also play a prominent role in various cabinetry operations.
Joining wood end grain sections can be extremely challenging with solid wood. This part of the wood soaks up the glue into the end grain section. But if you use a biscuit joint, you get added surface area.
The added advantage is that the slot is cut along the grain. It provides better contact between the two sections. You will find this type of joint useful with particular types of furniture and while installing wainscoting.
Butt joints are among the weakest of all joints. But if you add a biscuit to an end-to-end butt joint, it provides added strength to the joint. This is because of the additional surface area that the biscuit and slot offer.
Sometimes the very nature of a project may call for deliberately creating an offset joint to create what we call a “reveal.” It is created when we purposely create an offset between two sections of wood. A prime example is an apron on a table, where the table is inset a bit from its legs.
A biscuit joint is the most appropriate joint to use in this scenario. We use the biscuit jointer to cut the slots in the aprons. Then, we adjust the fence to accommodate the slots. You will not even have to use measurement to create reveals on all four corners of the table.
Sometimes you may need to add a bit more strength to a joint. For such purposes, you can use a double biscuit joint. Here, you cut the slot two times. You need to adjust the biscuit jointer after each cut, to accommodate two biscuits in the same slot.
What are the Disadvantages of a Biscuit Joint?
There is no perfect joint in woodworking and biscuit joints are no exception. Some shortcomings come from both the misuse of the technique and the inherent flaws like the joint. Here are a few drawbacks of biscuit joints:
Low Precision and Accuracy
There can be considerable misalignment with biscuit joints. A common reason for the misalignment of the two sections being joined is unsquare slots. Also, sometimes the slots may not be deep enough and it could result in exposed biscuits and depressions along the glue line.
Not Easily Covered
A good joint is invisible. But it is common for biscuit joints to become visible, especially while sanding down the area. You may have to make perfect joints, but if they start showing up when you do the final sanding it could spoil the look of your project.
Not as Robust as Other Joinery Techniques
If you compare biscuit joints to other joinery techniques biscuit joints emerge somewhat inferior. The mortise and tenon joint for instance is infinitely stronger than a biscuit joint.
A dowel joint, for example, is easily produced and it helps to not only align the wood but also add strength to the two sections of wood. This is as opposed to a biscuit joint which many argue is only good for aligning two pieces of wood and joining them.
When subjected to wood joint tests, you should not expect spectacular results from biscuit joints. For example, if you want to add strength to a dowel joint, you simply have to drill a bit deeper into the wood and use a longer dowel. There isn’t much you can do with a biscuit joint to add strength.
Uneven Biscuit Swelling
One of the unique characteristics of a biscuit joint is that the biscuit swells inside the slot due to the moisture in the glue that binds it. This binds the slot and biscuit together creating a firm joint.
Sometimes, the biscuit swells unevenly. It can result in a skewed or warped joint which can spoil the appearance of your project.
Are Biscuit Joints Stronger than Screws?
Two common types of joints in woodworking are biscuit joints and pocket screw joints. Both types of joints if executed well can produce flawless results.
With biscuit joints, you use a biscuit joiner to create slots and insert biscuits into those slots. The result is a secure joint between two sections of wood.
With the pocket screw technique, you drill holes into the wood at an angle. After dabbing on a bit of glue you drive self-tapping wood screws into the holes. Both techniques produce clean results and enjoy equal popularity.
Which technique is better? Is a biscuit joint stronger than a pocket screw joint? Historically, choosing between either two of these joints is a grey area. While the choice has a lot to do with money, the specific need of the job will determine which type of joint to use.
But the final verdict here is that neither biscuit joint nor pocket screw joints possess extreme strength.
Do Wood Biscuits Add Strength?
As we mentioned above, we cannot rely on a biscuit joint for strength. The best approach is to consider these joints useful for alignment purposes and not for adding strength.
However, certain types of biscuit joints can add some strength, especially on account of the glue used in the joint. So, we can conclude that although a biscuit joint is not as strong as many other types of joints, it can still add strength.
It is simple to make biscuit joints. But many things can go wrong like misaligned surfaces, uneven biscuit swelling, and defective slots.
The main thing to consider about biscuit joints is that they aren’t the strongest joints around. You always need to keep in mind that they are made from compressed wood. Also, there is a limit to the depth you can achieve with these joints compared with other joints like a mortise and tenon joint, or a dowel joint.
Due to the above reasons, you will find biscuit joints used on non-load bearing parts of wooden furniture like tabletops, cabinets doors, and in trim rather than for chair and table legs.
But if you are looking for flawless joints that will hold wood together indefinitely, you need to use biscuit joints. We hope you have gained enough information here to confidently use biscuit joints in your woodworking projects.