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You probably rely on your miter saw to make those perfectly square or angled cuts. It’s really important to be able to depend on this – to know that when you want a precise 90-degree cut, that that’s what you’re going to get. Following the instructions below will help you to ensure that you get the best cuts from your miter saw. While most people will set up their compound saw by putting a square between the blade and the fence, the best way to check whether your saw is cutting a perfect 90-degrees is to cut with it.
Prepare your test stock
You’ll need two boards to test with, ideally as close to the maximum width your saw can cut as possible. The wider the board, the more precisely you’ll be able to measure the angle it cuts. Your test boards will need to have one perfectly straight edge each.
Make a test cut
With the straight edges flat against the fence, make a cut. You can cut both boards at the same time. It is best to cut into the wood so that the blade has material on both sides. If you’re just cutting the end grain then the blade can deflect away from it, having an adverse affect on the cut and defeating the purpose of the test. With material on both sides of the blade the cut will be straighter and give a better representation of the angle.
Check the test cut
Place the flat edges on a flat surface and position the cut ends against each other. Look between them for gaps. If the boards do not meet perfectly then the blade is not cutting at precisely 90-degrees. Since both boards were cut at the same time, they both have the cutting error and therefore the misalignment is amplified. The gap is about twice the size of the angle your saw is off by. Readjust the saw as specified in the owner’s manual and make another test cut.
The desired result
What you want to happen is for the edges of the boards to meet uniformly from top to bottom without any gap.
Check the bevel
If you’re using a compound miter saw then it is also important to check that the saw cuts a perfect 90-degrees perpendicular to the table. Once again cut the two boards, this time with the flat edges down on the table. Repeat the steps above to make sure that the bevel angle is perfect.
Check the miter
Very similar to before, with flat edges against the fence cut an angle of 45 degrees.
Check the test cut angle
Place the two mitered edges together and place a square on the inside corner. If the edges are in full contact with the square then everything is fine. If there are gaps, then adjust your saw accordingly.
Create a line-of-cut fence
To make it easier to accurately position the material you are about to cut, you can create a sacrificial fence out of wood, which you fasten to the actual fence of your saw. Most fences come with screw holes for this purpose. Screw a piece of wood to your saw fence with a ruler underneath to create a gap for sawdust to escape through.
Most the line-of-cut cut
Remove the ruler and cut through the sacrificial fence with the saw.
Using the line-of-cut
Now you have a measure in your fence that shows exactly the cutting line of your saw. This makes it simple to accurately position material for cutting. The edge of the kerf in the sacrificial fence precisely indicates the line of cut of the saw blade.