1 Building the jig
To cut circles bigger than the capacity of commercial saber saw jigs, use a shop-made guide customized for your saw. The exact size of the jig can vary, but the dimensions suggested in the illustration at left will yield a jig large enough to cut a circle to the edges of a 4-by-8 panel. Begin by removing the blade from your saw and outlining its base plate on a piece of ^-inch plywood. Reinstall the blade and cut along the marks, making the section that will be beneath the base plate slightly larger than the plate. Lighten the jig by trimming it to the shape of an L, then cut out the notch for the blade. Screw the jig to the base plate, ensuring that the back of the blade is flush against the bottom of the notch. Use a pencil to mark a pivot line on the jig that is aligned with the teeth of the blade.
1 Building the jig
For cutting perfect circles on the band saw, use a circle-cutting jig custom-built for your tool like the one shown at left. Refer to the illustration for suggested dimensions. Use a router fitted with a dovetail bit to cut a M-inch-deep groove in the middle of the jig base. Then use a table saw to rip a thin, beveled board that will slide smoothly in the channel. (Set the saw blade bevel angle by measuring the angle of the channel edges.) Cut out the notch on the band saw. Then position the jig base on the saw table so that the blade lies in the notch and the dovetail groove is perpendicular to the direction of cut. Now screw the support arms to the underside of the jig base; the arms should hug the sides of the band saw table. Bore two screw holes through the bottom of the dovetail channel in the jig base roughly 1 inch and 3 inches from the unnotched end; also bore three holes through the bar.
Mark the circumference and center of the circle you plan to cut on its underside. Then, use the band saw to cut off the four corners of the workpiece to keep it from hitting the clamps that will secure the jig to the table as the workpiece turns. Make a release cut from the edge of the workpiece to the marked cir
cumference and veer off to the edge (above, left). Screw the pivot bar to the center of the workpiece through one of the bar’s holes (above, right), leaving the screw loose enough to pivot the workpiece. Turn the workpiece over and mark the contact point where the blade touched the circumference during the release cut.
3 Securing the workpiece to the jig
Clamp the jig base to the band saw table, making sure the support arms are butted against the table’s edges. Slide the pivot bar into the channel in the base and pivot the workpiece until the marked contact point touches the blade. Screw through one of the holes in the jig base to lock the pivot bar in place (left).
Completing the circle
Turn on the saw and pivot the workpiece into the blade in a clockwise direction (below), feeding the piece with your right hand until the cut is completed.