A Biscuit Jointer otherwise known as a Plate Joiner is a wood cutting machine which is used to cut out a shallow, oval shaped notch in each face of 2 pieces of timber so that they can be joined together using a biscuit.
This is a very simple procedure for joining two pieces of wood together where a simple butt joint would be too weak or the timbers being joined need to be joined totally aligned with each other.
It is possible to cut a biscuit joint using a router (information on this can be found in our cutting biscuit joints with a router project here), but for the purposes of this project we will be using the purpose-built tool for the job, a biscuit jointer.
What is a Biscuit Jointer?
As we have briefly mentioned, a biscuit jointer is a specialist tool specifically designed for forming the oval-shaped cut in a piece of timber to take a timber joint biscuit.
On a basic level, there is a small retractable cutting blade on the front edge of the saw that, when the body of the saw is pushed against the face of the timber you are cutting, the blade protrudes outwards and cuts into the timber face, forming a perfectly oval-shaped cut, just the right shape to receive a biscuit.
The tool is designed so that it can be easily adjusted to cut the slots required for the 3 main biscuit sizes of 0, 10 and 20.
It it also designed so that the cutting height can be easily set in that the thickness/height plate can be raised or lowered to determine where on the face of the timber the blade makes its cut.
When using a biscuit jointer is essential that you handle the tool correctly during use. This means that when it’s running you should have one hand holding the main body/casing and the other hand should be holding the handle. This will ensure full control of the tool at all times.
As with most timber cutting tools, you should also notice a vacuum attachment on the rear of your biscuit jointer. It is always advised that you attach an extraction device of some kind while the tool is running to get rid of any dust.
This will not only ensure that you are not covered in dust and debris while using you biscuit jointer, but the tool itself is kept fairly clean and free of dust that could otherwise clog it up.
Health and safety wise, this is very important, especially if you are cutting MDF as MDF is carcinogenic (could potentially cause cancer).
On the point of health and safety, while using a biscuit jointer you should always wear old clothes, suitable gloves, eye protection and also a suitable dust mask.
Setting up a Biscuit Jointer
Before you can simply start cutting away, there is some setup of the tool needed to ensure the joint is cut in the correct location, at the correct height on the face of the timber and at the correct depth for the size of biscuit you are using.
The first job is to set the cut depth of the blade for the size of biscuit you are using. With this particular Makita model we are using this is easily done (may differ slightly depending on the make and model of jointer you are using).
In this instance it was just a simple matter of turning the biscuit size selector knob until the correct number was selected for the size of biscuit we are using. As we are using a number 10 biscuit, 10 was selected on the dial.
One thing to mention at this stage is the depth stop screw. This sets the cutting depth of the blade dependent on the size of biscuit selected. You should not need to make any adjustments to this screw as it should be correctly set during manufacturer.
If you do inadvertently move it you may need to test the depth of your cuts again to make sure the blade is not cutting too shallow or too deep.
After you have made a cut and formed a biscuit joint you should always do a dry fit. This just means inserting a biscuit into the cut to make sure it fits as it should do.
On performing a dry fit you may notice that the cut is a little deeper and wider than the biscuit you are using. Don’t fear, this is intentional.
The depth allowance is to ensure that you can get plenty of glue down into the recess and the increase in width is to allow for some “wiggle room” to make an fine adjustments whilst fitting.
What are the Different Parts of a Biscuit Jointer?
As with most objects, when we can actually see what we are talking about, things often become much clearer:
To expand on the image above, we’ll now give a quick run down on each part of the biscuit jointer so that you fully understand what each part does:
- Power Cord: Supplies power for the tools motor (on cordless versions this will be replaced with a battery)
- Power Switch: Turns the tool on and off
- Cutting Angle Adjustment: Allows for cuts to be made at different angles, from a flat horizontal cut through to cuts at 90°
- Thickness/Height Plate: Used to set the height at which the cut is made on the cutting face of the timber you’re working on
- Blade: The cutting edge or blade of the tool. When not running, the blade is retracted inside the housing
- Biscuit Size Selector: Used to select the size of cut relative to the biscuit you are fitting e.g. 0 when using a #0 biscuit, 10 when using a #10 biscuit etc
- Depth Adjustment Screw: Used to set the cutting depth of the blade
- Handle: To be held at all times while the tool is running to ensure user has full control over the tool at all times
- Dust Bag: Used in place of a vacuum or dust extraction system. Catches timber dust and debris from the cutting blade
It may seem like there is a lot to think about here, but in reality, as long as you have set the tool to use the correct sized biscuit you’re using and set the correct cutting height and cutting angle of the blade, it’s really only a matter of attaching a dust extractor and using the power switch to turn the tool on and off when required.
What is a Biscuit Joint?
Setting up a biscuit jointer is a fairly simple task that we will explain in full a little later on, but before we go any further, let’s also just explain exactly what a biscuit is.
For those of you reading this that are new to both carpentry and DIY you may not be familiar with biscuits and biscuit joints and may be sitting there thinking; what biscuit should I be using? A Rich Tea, a Bourbon? Would a Digestive just be too big? Wouldn’t the jam all squeeze out of a Jammy Dodger and make the timber all sticky?
All valid questions indeed, but we should make it clear at this point, we’re not talking about sweet break time treats, we’re talking about timber biscuits as seen in the image below.
Normally made from compressed timber, a biscuit is a thin oval-shaped piece of timber that is inserted into a recess cut into each face of two pieces of wood that are to be joined together by a biscuit jointer.
The biscuit helps to keep the timbers exactly aligned as they are joined together and also provides strength to a joint that would otherwise be fairly weak.
The biscuit itself is designed so that when it comes into contact with a standard water-based wood glue, it expands, filling the joint fully, preventing any movement of the timbers and creating the strongest joint possible.
In comparison to other timber joints such as the mortise and tenon joint or halving joint, the biscuit joint is considered by many to be a fairly weak joint so it’s not really suitable to use in situations where considerable force will be applied to it.
However, it is more than suitable for use lighter applications where any forces applied are minimal, where perfect alignment of the timbers being joined is critical or to prevent the joint from being pulled apart.
What if I Make a Mistake When Cutting a Biscuit Joint?
Mistakes happen! This is true for almost all things in life and is certainly no different when it comes to biscuit joints.
The most common mistakes that are made are either cutting the biscuit recess too deep for the biscuit you have, cutting the joint in the wrong place or cutting it at the wrong angle.
If you have ever done this, chances are you have had to scrap the timber in question and start again, but there is no need to do this, you can in fact repair the timber and start again.
To make a repair, simply apply plenty of glue to the incorrectly formed cut and then insert a suitable sized biscuit.
Push the biscuit in firmly ensuring is cannot fall out or creep out and leave it until the glue has fully cured.
Once the glue is fully dried, cut the biscuit down until it’s almost flush with the face of the timber and then use a plane or sand paper to plane or rub it down until it is fully flush with the surface.
Once so, you can now re-cut your biscuit joint correctly.
How to cut a Biscuit Joint Using a Biscuit Jointer
You should now be a little more familiar with your biscuit jointer in terms of what needs to be done to set the tool up correctly, what you are precisely trying to achieve by cutting a biscuit joint e.g. align and strengthen a joint and also what a biscuit is and how it works.
With the above in mind, it is now time to actually use our biscuit jointer for the purpose it’s intended:
Mark Biscuit Joint Location on Timber
Before making any cuts at all, we first need to know the precise location of where we are going to make our cuts.
Place the two pieces of timber that we’re going to join together and make sure they are lined up exactly.
Using a pencil, mark a line across both timbers in the location that each of your biscuit joints are going to go.
When marking up your joints, one of the most important points to consider is ensuring that none of the joints are too close to an edge. If too close, when you make your cut, the blade can easily burst through the side of timber and ruin it.
Set Cutting Height
Once you have marked the location of your biscuit joint(s) the next job is to set the cutting height on your jointer so that the blade cuts at the correct depth on the face of the timber.
Firstly, measure how thick your timber is or measure down from the top of the timber to the location of your biscuit joint.
Ideally, the joint should go at the centre of the timber, but if you’re joining to a particularly long timber then this may not be possible.
For the purpose of this explanation we are jointing two pieces of timber that are 16mm thick. Now that we know the thickness, in this case 16mm we now divide this by 2 which gives us 8mm. So we want to cut our joint at 8mm.
Holding your biscuit jointer on its side, loosen the screw that holds the thickness/height plate firmly in place (normally on the front of the plate) and then move the plate upwards until the arrow points to 8mm. Once set at the correct height, tighten the screw to hold the plate in position.
Set cut Depth for Size of Biscuit
With the correct cutting height now set, it’s now time to set the correct cutting depth of the blade for the size of biscuit your are using.
On most modern biscuit jointers this is a job made easy via the “biscuit size selector knob”, normally located on the opposite side to the height scale and cutting angle adjuster.
Simply turn the knob until the size of biscuit you’re using is aligned with the arrow.
As we have mentioned above, just in front of the biscuit size knob is the depth adjustment screw. This controls the depth that the blade cuts to.
If you slide the tool forwards (holding the height plate) you should see that the depth screw touches the biscuit size selector and stops the tool from going forwards any more (or the blade protruding any further), thus setting the cut depth.
Do not touch the depth screw as it has been set correctly in the factory! If you do you will need to reset it to the correct cutting depth
Set Cutting Angle
In most cases you will be cutting a straight horizontal biscuit joint in each face of two timbers. In this instance you won’t need to make any adjustments at all as the tool should be set to form this type of cut as-is.
However, if you need to make a cut on an angle such as forming a biscuit joint on a 90° mitre joint (more on mitre joints in our project here) then you will need to make your cuts at 45°.
If this is the case then you will need to simply loosen the cutting angle adjuster and move the scale around until 45° is set and then lock the adjuster off again.
Once the correct angle has been set you can then go ahead and start cutting.
Align Biscuit Jointer and Make cut
With your biscuit jointer now set up and ready to go, all you need to do now is start cutting away.
Position the thickness/height plate onto your timber. Make 100% sure that the plate is totally flat down on the timber itself.
Move the jointer so that the small cut location arrow on the rear of the plate is aligned with the mark you made on your timber. Once this is so and you’ve made sure the plate is flat on top of the timber, switch on the power.
With the motor running and the blade rotating, ensure you’re holding the tool correctly e.g. one hand firmly on the main body and the other holding the handle, slide the jointer in so that the cutting blade engages with the timber.
Continue to push gently forwards until the depth screw hits the biscuit selector and the tool stops moving.
Once it stops you’ve now completed your first cut.
Repeat the above for any other cuts you need to make.
Test Fit Biscuit and Joint
With all of the biscuit cuts now made, the next job is to do a dry fit to make sure all fits as it should do.
To do this simply insert a biscuit into one of the joints and then fit the timbers together. If all is correct then the timbers should fit together seamlessly. All faces and edges should be flush and there should be no gaps between the joint itself.
Glue Biscuit Joint up
Once you have made sure that all fits as it should do, the final job is to glue everything together.
The gluing process essentially has two purposes, firstly to bond the timbers together and secondly to cause the biscuit to swell inside the cuts creating an even firmer and stronger joint.
Using a standard water-based wood glue, pour some into a small container and use a small paint brush to brush the glue right down into each recess, over the joining faces of each piece of timber and also all over each biscuit.
Once everything has had a good covering, fit the joint back together again, giving it a good squeeze to make sure it’s pressed fully together.
Once fully fitted, use some suitable sized clamps to clamp everything up until the glue has fully dried. Make sure any and all clamps are clamped up square and are not causing the timbers to twist as this will cause the joint to open up slightly and create gaps.
Once everything’s clamped up, use a damp cloth to wipe off any glue that has squeezed out of the joint.
With everything fitted together, clamped up and cleaned up you have now successfully cut a biscuit joint using a biscuit jointer, good work!!