How to Cut Accurate Circles in Plywood?
I want to cut accurate circles in a top grade of plywood to be made into Lazy Susans. I would like to know the best method, and tools or jigs to accomplish this. We have a selection of fine routers, band saws, saber saws, etc. available. We want to band the cuts and deliver a high finish to them. What do you suggest? - Bob Koenig
Chris Marshall: Always nice to have tool options at your disposal! Regarding cutting those plywood circles, if I was making just one Lazy Susan, I'd probably use a plunge router mounted on a circle-cutting jig. Drill a small hole partway into the bottom face of the plywood (where it won't show anyway), set the circle-cutting jig to the radius of circle you want, and then cut the circle round in a series of several deepening passes with the jig's centerpoint fixed in the pilot hole. Either a straight bit or an upcut spiral bit will do this job nicely, but be sure to use sharp bits to minimize splintering when the bit passes through to the other "show" face of the plywood.
Alternately, you could cut these circles on a band saw using a circle-cutting jig made for that machine. A band saw with a sharp, fine-tooth blade will provide clean edges, and it's easy to find plans for a band saw circle-cutting jig online. Still a third method would be to cut a round template from 1/4- or 1/2-in. MDF or Baltic birch plywood. Then cut your plywood lazy Susan tops slightly oversize, secure the template to them with a few pieces of double-sided tape, and use a pattern or flush-trim bit in your handheld or table-mounted router to trim them to final size. This last method is probably the most “goofproof” and could also provide you with the cleanest edges for banding with wood or veneer. If I were going to make lots of lazy Susans, this last option would be my pick. It's fast and simple.
Tim Inman: Depending upon the size of the circles, I would suggest either a band saw jig or one for the router. I use my band saw jig for smaller circles (up to about 24-inches dia.). I use my router for anything larger. The band saw leaves a "sawed" edge where the router is more perfect. But, the band saw is so much faster and easier. I can't give the whole set of instructions for constructing the jigs here, but the basics are the same for either tool.
My band saw circle jig is a false table that includes a sliding bar embedded into it. This bar has a spike on one end that acts as the centering point for the circles. I can slide the bar in and out to adjust for the radius of the circle I want to cut. You can find plans for these quite easily. The router jig is similar, except the bar for the router jig is fastened to the router. The point or center spike is on the far end. Visualize a trammel bar compass and you'll have the idea.
I use the band saw jig to cut circles for the bottoms of turned bowls and cups all the time. It makes quite accurate circles, FYI.