To produce smooth-walled mortises with your hollow-chisel mortiser, it’s crucial that the face of the chisel be precisely parallel to the machine’s fence, so each square recess the chisel chops is perfectly in line with its neighbor. You can try aligning things with a square held to the side wall of the chisel, but the chisel is small, making it a challenging reference surface.
Instead, I clamp a straight piece of wood, about 12 in. long, to the front or back face of the chisel, and sight down the stick to see if it’s parallel to the fence. The steel ruler from your 12-in. combination square also works. The long stick magnifies any inaccuracy, making it easy to see if the chisel is parallel to the fence. You can also measure from the fence to each end of the stick to be really sure. Think of it as a winding stick for the mortising machine.
—MARK MOORE, Annandale, Minn.
Illustrations by Dan Thornton
From Fine Woodworking issue #295
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