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A biscuit joiner is a tool used to cut shallow half moons into materials that are going to be attached together in a joint, usually at a 90 degree angle.
You need to know how to use a biscuit joiner to cut these slots correctly in order to firmly construct the joint, where pressed wood biscuits will expand with the addition of glue. This fills the slot that lays between the two pieces of wood you are putting together.
- How to Use a Biscuit Joiner
- Considerations for Using a Biscuit Joiner
How to Use a Biscuit Joiner
You will need to start out by setting up your work area correctly with clamps and a stopper, which we will explain a little further down the page. Eye protection is recommended due to the sawdust and other debris that a biscuit joiner can expel, but many of them do come with an attached dust bag that will help contain it.
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Biscuit Joining Edge to Edge
When you want to joint multiple boards or planks together to create a wide, flat surface, biscuits can help increase the strength between the boards. This is the easiest situation in which to use a biscuit joiner, as all of the boards should line up flat on the same surface. In addition, the biscuits will help tremendously with aligning the boards.
- Place the different boards together how you want them to mate in the final joint position.
- Mark a line between the two boards with a pencil where the center of the biscuit grooves will be cut. Keep about 4” to 6” between the center marks depending on the size biscuits being used.
- Separate the boards.
- Place the first board against the stopper that is clamped to the table, with the edge that is being cut facing away from the stopper.
- Set the plunge depth on the biscuit joiner to the correct biscuit size.
- Check that the adjustable fence is set to the correct stock thickness. Most default settings are for 3/4″ boards.
- Line up the center mark on the joiner with the pencil line you have marked.
- With the biscuit joiner at its starting position with the blade apart from the board, start the motor and let it get up to speed.
- Press the blade firmly and smoothly into the board, then back out.
- Stop the motor, move on to the next slot and repeat.
- Repeat for each board.
90 Degree Biscuit Joints
You will often use a biscuit joiner when building furniture such as a bookshelf or desk, where you need to create a ninety-degree joint (also known as a T joint or L joint) between an end cut of wood and an edge or flat face. Because of the porous nature of end cuts of wood, the glue needs additional help to bind, which is where the biscuits come in.
- Lay down the piece of wood where the biscuit will be cut into the flat face, with the face that will be cut pointing up.
- Measure from the end of the board to where the edge of the end piece will be attached, and mark with a pencil on the side of the board.
- Lay the piece that will have the end cut on top of the flat cut piece, parallel, with the end that will be cut lined up with the mark you just made. The boards should have their flat faces against each other.
- Clamp the pieces to each other and the workbench. The ends should be offset.
- Mark where you want the biscuit slots cut into the top board.
- Set the biscuit joiner to the correct biscuit size and stock thickness.
- Cut the top board: Using the bottom board as your base instead of the workbench, line up the center marks on the top board, and cut into the end with the biscuit joiner.
- Cut the bottom board: Pick up the biscuit joiner and turn it so the bottom is pressed up against the end you just cut. That will be your base. Line up the center line on the bottom of the joiner with your marks and cut slots into the bottom board.
The fence of some biscuit joiners can be switched between flat and 90 degrees, and specialized models can even be rotated to angles between the two. This will allow you to cut both pieces of wood that will be on the joint with the tool in the same position and using the same stopper. That may come in handy when making an L-joint – the adjustable fence will provide additional guidance and support.
Mitered Biscuit Joints
A miter joint has two ends cut at a complementary angle to each other, usually at 45 degrees. Corners of a picture frame are one example, and you can also see mitered joints in action in baseboards and molding. A biscuit joiner can help align these corners so the edges meet at a perfect angle.
- Line up the mitered corner in its final position.
- Mark a line between the two pieces of wood stock an equal distance from the outer and inner corners. There should be a matching line on each end piece.
- If you are joining more than two pieces, it is a good idea to number every piece so they can go back together in the correct order.
- Separate the wood pieces.
- Because the edge you will be cutting into is at an angle, it is important to clamp these pieces down to the work bench. An angled stop would not be very stable, and holding the piece with your hand at that angle is not recommended.
- After one piece is clamped, cut into the end with the biscuit joiner, then unclamp it.
- Repeat the clamping and cutting process with the other wood piece or pieces.
Putting Together Biscuit Joints
Oblong pieces of pressed particle wood called “biscuits” are glued into slots between pieces of harder wood to provide extra stability instead of just using glue by itself to keep them together. After cutting the slots for them with the biscuit joiner, you will need to bind your cut pieces of wood together with biscuits and glue.
- Place the boards in the approximate final layout to make sure they are lined up correctly.
- Add glue in the slots of one board, and insert biscuits into the slots. Consider spreading the glue around the slot with a glue brush.
- Add glue to the slots of the board that the first one will mate with, then join the boards together with the biscuits between the two.
- Clamp the boards tightly and allow them to dry completely.
As the glue soaks into the biscuits, they will begin to swell, filling in extra space and adding additional binding pressure between the pieces of wood. Try not to use too much glue since it can get pressed outside of the bonding area. If extra glue squeezes out of the slots when clamping, wipe it off immediately.
Follow the glue manufacturer’s instructions on how long to leave the wood pieces clamped together. They will often give you two different lengths of time – one number that will allow you to remove the clamps, and another that will tell you when the glue is completely cured. Allow for the full cure time if you are going to be performing any more woodwork to the piece and before adding pressure.
Considerations for Using a Biscuit Joiner
The decision on whether to use a biscuit joiner, one of the many other types of joints, or simply gluing your stock together is very important. Some joints may need extra support from something like a biscuit, where others may be fine with just glue. In most cases where an end cut is being jointed, a biscuit joiner will probably be the correct tool to use.
With natural wood and on the edge or flat of the stock, you may be able to create a joint without a biscuit or other support while only using glue. Wood pieces that need to connect to the end, with its open porous grain, will still need joint support. Other materials, however, will usually need help from a biscuit on its edges as well as sides.
Here are some manufactured wood products that can also benefit from using a biscuit joiner:
- Plywood: On any surface other than the flat face, an additional support bit like a biscuit is necessary when bridging or jointing pieces of plywood. Every edge of plywood acts like an end cut of hardwood, where the porous layers that are pressed together absorb too much glue to make an effective bond work without the additional support of a biscuit.
- Particle board: Similar to plywood, the ends, and edges of particleboard are very porous. We want to make sure that the glue binds solid material instead of soaking it into wood stock away from where we want the bond to occur.
- Medium-density fibreboard (MDF) – Even though it is denser than plywood and particleboard, the ends and edges of MDF boards are still more porous than edge cuts of natural wood. We recommend using some sort of joint connector with MDF, and a biscuit joiner will help you with that.
History of the Biscuit Joiner
The concept of adding a piece of wood as a support between other pieces of wood is not a new one, but the biscuit joint method is fairly recent. Because the cuts do not go all the way through the wood, they do not weaken the overall integrity of the wood like some other jointing cuts may.
Originally called the Lamello joining system, as he was working for Lamello at the time, Hermann Steiner invented the method to create a strong, easy-to-replicate joint between two pieces of wood in his carpentry shop in 1956.
The biscuit joiner that we use now is portable and has a circular saw. The first versions were stationary, and the cutting edge was very different from what we are used to today. Biscuit joiners as we know them now were not truly available to the public until 1968.
Biscuit Joints vs. Mortise and Tenon Joints
In just about every scenario that you can imagine, mortise and tenon joints will provide a more stable joint than a biscuit will. That is not to say that a biscuit joiner is not useful, because the ease of use and application is much easier with a biscuit joiner than putting together a successful mortise and tenon joint.
When using a biscuit joiner, all you need to do is cut a small, pre-defined slice out of the wood that you are going to insert the standard sized biscuit into. With a mortise and tenon joint, you will need to cut the end of one of the stock pieces to insert into the other. This can be much more difficult than adding a binding piece of wood and glue between two pieces of stock.
If we compare a biscuit joint to a mortise and tenon joint, the mortise and tenon will come out ahead in terms of strength and longevity. However, we feel that in many situations, the ease of using a biscuit joiner to create a solid joint outweighs the overall strength of the mortise and tenon.
Taking Care of Your Biscuits
After you use your biscuit joiner to cut slots in the pieces you are putting together, you will need to glue pieces of pressed wood into the grooves. These oblong, football shaped chunks are called biscuits. Even though they look like a nice cookie or biscuit to enjoy with tea, we really do not recommend eating them.
Woodworking biscuits are usually made of pressed beech wood, gathered from lumber shops after milling beech planks. Biscuits are available to purchase in a few different standard sizes that match up with the settings on a biscuit joiner. #20 is normally the largest size at 2 ¼” long, while size FF is only 1 ¼”.
These biscuits are made not only to create strength between joints but also to fill areas that they are inserted into. Because of the pressed nature of the wood used in their construction, biscuits will swell when moisture, like glue, is added to them. While this is on purpose, if you leave biscuits out in the open, they may absorb considerable moisture and end up swelling.
How to Deal With Biscuit Swelling
- The best way to prevent biscuits from swelling is to store them in an airtight container. Mason jars work very well for this purpose, while plastic kitchen containers can be functional as well.
- Add a packet of silica gel to your biscuit storage container. You may find these packets in shoeboxes, or you can order them online. Do not tear them open! They are designed to work by just adding the packet to the container you want to help keep moisture-free.
- If you find your stored biscuits become swollen no matter how you store them, you may consider purchasing a biscuit press. This is a tool that you insert woodworking biscuits into, then crank by hand to flatten the biscuits out to a consistent thickness.
Setting Up a Biscuit Joiner
Setting up your work area to get ready for projects with a biscuit joiner will normally consist of cleaning off your workbench and getting a few clamps ready. For your work surface, a work bench will be your best bet, but any wide, flat surface that you can use clamps with should work as well.
Look through your scrap or extra wood to try to find a straight board or plank that you can clamp directly to the table. Use this as a sort of a backstop that you can mount the wood stock you will be cutting up against. In this way, you can avoid clamping down every single piece of wood that you will use the biscuit joiner on.
For smaller wood stock where you can good grip, or if you have confidence in being able to hold larger pieces by hand, you may be able to get away with not clamping or setting up a stop. This does not mean that it is the recommended method, and never place your hand flat on the opposite side of the biscuit slots you will be cutting.
Using a Biscuit Joiner With Narrow Wood Stock
When dealing with narrow stock, you can use a biscuit joiner even if the biscuits you have may extend past the edge of the wood. Definitely clamp or use a backstop when dealing with smaller pieces where the blade may become exposed.
Place the narrow wood pieces together in their final position, and place a biscuit where you would like it to go to provide the most strength. If the end of the biscuit is going to be exposed, try to make it on an outside edge that will be easy to get to. Mark the boards from the middle of the biscuit.
After cutting the boards with the biscuit joiner, glue the biscuit as normal but with the extra end sticking out of the wood stock. After the glue is completely dried, simply cut off the end of the biscuit and sand it down to make all the edges flush.
Marking Wood Stock for Biscuit Joining
On the work bench, lay out the stock pieces that you will want to join together, and line them up with their grains going in the same direction, and the tree rings pointing down in the same direction. Have a plan in place for which side will be facing out, and which side will be behind.
Make a mark on the sides of the stock that will be displayed so you are sure to keep them matched. This will also ensure that you do not cut into the the side with the front-facing markings.
When jointing planks edge to edge, one of the tricks to planning to place specific boards in a certain order is to mark them using long diagonal lines or triangles across the planks. Since the lines will only match up in one specific formation, you should be able to easily keep track of the order they will be placed in.
Tips for Using a Biscuit Joiner
- Use the largest biscuits that fit your joint. Fewer large biscuits will have more holding strength than more small biscuits. You can use biscuits that extend past the edges of your project as long as you are willing to cut and sand them after the glue has dried.
- For stronger biscuit joints, cut out slots for double biscuits. If you have enough vertical space in the joint you are connecting, consider cutting two slots on top of each other into the joint. These can be separate or combined into one large slot.
- When using double biscuits, alternate the grain direction. Instead of pointing the grain of the biscuits the same way, having the grain of each facing a different direction will increase the strength of the joint.
- Emphasize the biscuit joiner center line. Sometimes the center line on a joiner is difficult to see. Use a permanent marker to make the line easier to see. Do not forget to mark the center line on the bottom as well.
- Keep cuts straight by using two hands. It can be easy to cut a biscuit off center or at an angle when only using one hand, and especially when placing the weight of the biscuit joiner on the fence against your stock. Keep one hand on the handle, but the other on the fence, helping to hold the tool in place.
Out of the many ways that you can create a strong and effective joint, using a biscuit joiner is one of the easiest methods there are. There are different situations where this tool and process are especially effective like attaching end cuts of wood, since cut ends are notoriously difficult to glue without another form of binding and alignment.