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Cutting Out Circles
21st in a series of articles by Barb Siddiqui
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Many woodworking projects call for arcs and circles that require accurate cutting, and depending on hand/eye coordination to accomplish the task will usually result in an imperfect edge at the cut line. If, in a beginner's shop, equipment is limited, what you have can still be accessorized to get the job done. There are many ways to do this; here are some common methods using three different tools.
A handheld jigsaw can do a decent job on circles larger than about three inches in diameter. If you trust yourself guiding the tool accurately to a line, cut one-sixteenth inch outside the line and plan on sanding or filing it smooth afterward. A more accurate circle can be made by attaching a shop-made trammel below the foot plate of the jigsaw, as long as the radius of the circle being cut. Use 1/8" tempered hardboard cut into a narrow teardrop shape, wide enough at the outer end to attach with double-sided carpet tape underneath the saw. Before attaching it, cut a clearance slot for the protruding blade in a V-notch so you can sight through it to guide to the line. At the narrow end of the jig, use a small nail through to the center of the workpiece, to rotate the tool around your marked circle or arc. By drilling several 1/16" holes centered along the length of a long trammel, your centerpoint nail can be moved to different points, making the jig more versatile for future use.
Another standard tool to use for cutting circles or arcs is the handheld router, either using a template and a bearing-guided router bit, or a sub-base with an attached trammel jig similar to that described for the jigsaw. Trammels can be made from plywood, hardboard, or acrylic, and fitted to the base of any model router with longer than ordinary sub-base screws, available at hardware stores or through tool catalogs.
Routers, and the jigs necessary to utilize them, are a full subject unto themselves. I'd recommend purchasing a copy of either Woodworking With The Router by Bill Hylton and Fred Matlack, or Router Magic by Bill Hylton, for guidance on the many ways to cut circle patterns with a handheld router.
The third, and most common way, to cut curves, circles and arcs is by using a band saw. If your shop lacks even a small band saw, consider setting aside your shekels to acquire one. Many experienced woodworkers claim if they were abandoned on a desert island (with electricity) and could have only one power tool, a good band saw could do all the cutting they'd need for woodworking.
Again, there are several ways to accomplish this job. One way is to support the workpiece as it is turned and run the marked circle through the band saw blade by hand, eyeballing an accurate curve just outside the marked line and sanding it to perfection afterward. Some sanding will be required no matter what method you use, as a band saw generally leaves a rough sawn edge, especially if a blade is not sharp.
A slightly more complicated, but more accurate, method is to build an additional tabletop of plywood, cut to the center so it surrounds the band saw blade and somehow screws on or clamps on from below to secure it to the band saw table. The circle cutting use of this added table comes into play by adding a sliding bar of any desired length, either using an angled cut so the bar rides in an angled slot similar to a dovetail joint, or cutting the mating pieces with rabbet cuts so the movable bar slides in a T-slot arrangement to hold it in place.
This slider moves in and out of the wooden table at a 90º angle to the cutting action of the band saw blade, and is set to the radius of the desired circle, with a centering pin or a nail head set into the bar and securing the workpiece above it. If the radius of the cut is larger than about 8", an outfeed support stand may be necessary to support the waste of the workpiece while rotating it through the cut. This is often handled with a hinged extension leaf resting on a fold-down leg support that reaches the floor.
Any method one chooses for cutting arcs and circles in a workpiece is dependent upon the equipment available, but even large projects can be accommodated; maybe not as elegantly or simply as one would like, but by sheer determination, and with some ingenuity and patience. Figure out how to support the workpiece, and how to best guide the cut. Plan ahead by removing any waste material beyond the pattern, and make relief cuts straight into the pattern line to reduce the tension on a turning blade. We all learn by doing. Rest assured your second large circle-cutting project will look better than your first, and the third project better yet.