Wood biscuits, also known as Wood plates or Wood wafers, are used for edge or corner joining. Slots are created with a biscuit joiner and the wood biscuits are inserted. Water based glues cause the biscuit to swell, thus creating a ‘locked’ joint.
If you want your joints to be strong, you should use the largest biscuit you can find. If the biscuits are only being used for alignment, then you can choose any biscuit size you like.
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Wood Biscuit Sizes and Common Uses
In woodworking, biscuits are oval-shaped, compressed pieces of wood that are highly dried. Different sizes are available with different uses.
FF, 0, 10, and 20 are the most common ones, from smallest to largest.
The FF size is 1/2 inch by 1 3/8 inches, and they can be used for small projects.
The #0s (which are 5/8 inch by 1 3/4 inch) are typically used for larger workpieces than FFs, but they cannot withstand much tension. Typically, they are used for projects like picture frames, which do not require a great deal of stress, or narrow applications, where larger biscuits can not be easily accommodated.
Generally, the #10 (which measures 3/4 by 2 1/8 inches) is found both in specialty shops and in home centers. They can handle quite a bit of stress and are ideal for most woodworking projects.
The biggest are #20 (which measures 1 inch by 2 3/8 inches). This is the tough stuff: they can stand a lot of weight and stress. These are great for tabletops, drawers, and anything that will be used regularly.
What Size Biscuit to Use?
For stronger joints, use the largest biscuit you can fit where the joint will be placed. Simply press the biscuit joiner against the surface where you plan to make the joint to check whether or not it will fit.
After that, check how much of the blade comes out: if you have enough material (let’s say 1/4 inch) between the blade and the opposite edge of your board, you are good.
Choosing a smaller biscuit size is better if you have less material left. As an alternative to using a larger biscuit, you will use as many biscuits as you can fit along with your wooden board.
In the case of alignment, just about any size will do. Use enough biscuits to accomplish your goal. I would recommend picking a smaller size if you are working with narrow boards.
FF biscuits are a good option in this case.
What are FF biscuits? Should I use them?
Biscuits make excellent joinery products, as I’m sure you agree. However, they are limited in many ways. The biscuit slot must be long enough to accommodate the biscuit.
Even the smallest biscuit, the #0, needs a slot that could be too big for certain spots. The FF biscuit was developed to solve this problem.
FF (which stands for Face Frame) biscuits are smaller, and they have a rounded shape rather than an oval one. Therefore, they are able to handle smaller workpieces since they take up less space. How cool is that? There is one drawback, however.
A smaller slot is needed to accommodate the smaller biscuits: biscuit joiners usually have a blade with a diameter of five inches, so you would have to switch to a smaller blade.
Some machines don’t allow you to change the blade. While other machines they can be easily swapped for a smaller one. Something to be aware of when you purchase a biscuit joiner.
What Biscuit Size for ½” Plywood?
Making furniture from plywood means making joints that are clean and inconspicuous. In that case, you might prefer a biscuit joint.
If you purchase cheap plywood, the biscuit may expand too much, so the surface will be deformed. You should be able to accomplish this by working with quality plywood that has at least seven layers.
For a test, you can make some joints with some scraps of plywood, let them rest for a week, and see if anything stands out.
A second factor is the plywood’s thickness. Our material in this case is 1/2 inches plywood, which is quite thin. The material needs to be good in this case, so follow the process I explained above.
What Biscuit Size for ¾” Plywood?
With 3/4 plywood, either #10 or #20 size biscuits will work. If unsure then, as before, do a test on scrap material and wait a sometime to see what happens and if any problems arise.
What is the recommended number of biscuits to join wood?
Use as many biscuits as you can fit into the joint for a strong connection; however, if you plan to use the joint to align the parts, a good rule of thumb is to use two biscuits per foot of wood.
It is recommended to space them about 6 to 8 inches apart for something like a tabletop, something that needs some stability. Alternatively, you could space them wider, say around 10″ – 12″, if you’re making something that doesn’t need so much strength.
Moreover, it really depends on how thick the material is. For example, a thicker material makes it possible to fit two biscuits together by creating a slot that is twice as wide.