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This is a useful jig that’s also fun. The workpiece turns on the jig’s pivot point and cuts circles and arcs with a wide range of radii. I thread the jig with a 1/4-20 tap, so it will accommodate any size pivot point I care to grind from a bolt. They can range from the full 1/4-in. diameter for heavier pieces, to a needle point for delicate work.
Interchangeable pivot points. Pivots can be as small as a sharp point, or larger for heavier workpieces.
To avoid a center mark on the stock, attach a sacrificial surface to the underside of the workpiece with double-sided tape.
The pivot point is in a sliding arm dovetailed into the body of the jig.
Click to enlarge.
This arm can be moved gently forward while you rotate the stock into the blade, initially creating a spiral-shaped cut.
Spiral into the circle. With the saw running, gently push the arm forward while rotating the stock into the blade (see images of the arm below). Once the stop reaches the end of the guide track, the blade starts to cut the actual circle (above).
A stop block clamped to the outboard end of the arm hits the body of the jig when you reach the correct radius, and only then does the blade begin to cut in a circle.
Attach the stop. After measuring the distance from the pivot point to the blade (circle radius), clamp the stop on the underside of the arm at the end of the guide track. (Click on individual images above to enlarge.)
Make the track and sliding arm of a hard and stable wood. The sliding arm and track are dovetailed so that the arm does not tip out of the track, and the bearing surfaces are waxed. The track could be dovetailed directly into the body of the jig, but it is easier and will remain more accurate if a strip of hardwood is dovetailed, then set into a dado.
Keep in mind: The bandsaw blade must be narrow enough to cut the desired radius, and the cutting edge of the teeth must align with the centerline of the pivot point on the sliding arm. If the pivot is forward or back of the teeth, the blade will not cut freely and the circle will not be true.
-Excerpt from Five Essential Bandsaw Jigs, FWW #180
Photos: Marcia Ryan
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