Square or angled woodworking projects are easier to make than round or curved items. The majority of woodworking tools are geared to making straight cuts and angles. Bandsaws and scroll saws are two pieces of equipment that will cut curves but the curves are limited to the throat depth of the saw. A jig saw will cut a curve but the line is only as straight as the individual moving the saw manually around the curved line. A good piece of equipment to use to cut arcs, curves and circles is a router.
A router uses a circle trammel to create a wood cutting compass. Understand there are two circle trammels. One is a simple circle trammel and the other is a router circle trammel. They both cut circles but the router circle trammel cuts a wider variety of shapes and is more reliable.
All arcs and circles require cuts that go both with the grain and against the grain of the wood. Minimize tear-outs within the cutting area by making numerous shallow cuts until the shape has been cut through the wood.
A plunge router works better for making curved designs. A conventional router has more drag and can cause more tear-outs in the wood. The plunge router allows each pass to be deeper than the conventional router.
Create less tear-outs in the wood by using a spiral upcut bit. Most individuals would assume a straight bit would handle the job more efficiently. The straight bit works very well with the grain of the wood. When cutting against the grain, the straight bit will cause tear-outs if the cut is too deep. The straight bit can be used, just be careful with the depth when cutting. Check frequently for indications of tear-outs. Experiment on a scrap piece of lumber prior to making the final cut.
Most trammel pivots come with a pin to secure the device. The pin causes issues when cutting a curved line. Either replace the pin with a screw or nail to secure it to the wood or hold the pin down firmly when cutting.
It is possible that successful passes will leave a mark on the edges of the cut curve. Avoid sanding them out by setting the trammel to cut a radius 1/32-inch larger than the desired shape. Readjust the trammel on the last pass and trim the curve to the desired size with the last pass.
The majority of circle or arced cuts will be completed from the backside of the woodworking project. This allows for the pin mark to be on the back of the project. In the case that the circle or arc cut must be made from the front, mold the edge of cut with the trammel as a guide to the router.
Woodworking Plans and Projects: Rout Curves and Circles
Woodworking Tips: Router Circle Cutting