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How do I make perfect circles with a jigsaw?

Elevate the workpiece on a 4×4 to provide clearance for the blade, and rotate the panel as needed. Cutting slowly reduces blade flexing and gives the best finished edge.

Q:

I don’t have a bandsaw or router, but need to cut a circular tabletop. Can I outfit my jigsaw with a trammel to do the job?
—Brian Davis, Normal, Ill.

A:

Although a jigsaw wouldn’t be our first choice for cutting circles, Brian, it can be done. Begin by making an auxiliary base from 14 " hardboard. Align the edge of the saw’s foot with one end of the hardboard and cut a slot for the blade. (We got good results cutting circles with a 10-tooth-per-inch blade.) Then attach the saw with screws, if your base has them, or double-faced tape if it doesn’t. Mark a line on the bottom face of the base parallel to the edge and aligned with the blade teeth. 

Measure from the inside edge of the blade and mark your desired radius along the line. Drill a hole for a finish nail at this point, and at the centerpoint of the circle on your workpiece. When marking the centerpoint, either measure from the workpiece edge, or drill a blade starter hole tangent to the edge of the circle and chisel a flat surface where the hole and circle meet. When you put the saw in place, the blade must rest snugly against the edge of the workpiece (or the flat edge of the hole) without deflection.

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An auxiliary base eliminates tear-out and also reduces lateral blade movement. You may need screws longer than the stock screws to attach the auxiliary base.

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