How do you know when your miter gauge is set exactly at 90°? Here’s a method I learned years ago, before I could afford a precision square to check the cut.
You’ll need a 24″ long board that is flat and straight, with perfectly parallel sides. It should be about 6″ wide. You’ll also need a fence for your miter gauge, about the same length as the board. Make sure it’s straight, too.
Draw a triangle in the middle of the board, so you can tell which face is which. Crosscut the board through the triangle. Turn off the saw. Flip over one side of the board and pull both pieces tight against the fence. Slide the pieces together, so the two freshly sawn surfaces touch each other.
If your miter gauge is right on the money, there won’t be any gap between the two pieces.
If there is a gap, the miter gauge is off. You’re looking at double the error. Adjust your miter gauge and put the boards back in their original position, so you see the whole triangle. Butt the boards together and make another crosscut, centered on the first cut. Flip one board and…well, you get the idea.-Tom Caspar
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