Cutting large, accurate circles in timber may seem daunting, especially without specialised tools. However, a simple circle-cutting jig made from basic materials and used with a trim router can provide highly accurate results. This method is ideal for projects like restoring round table tops, crafting curved furniture, or fabricating large decorative panels.
Begin by selecting a durable, smooth material for the jig base. Birch plywood with a film face is ideal. It’s strong, glides well over surfaces, and can withstand repeated use. The length of the jig should match or exceed the radius of the desired circle. For example, a 1,400 mm diameter circle requires a jig measuring at least 700 mm from the pivot point to the router bit.
Next, construct a collar to hold the trim router in place. Trace the base of the router onto a scrap of plywood, then cut it out using a jigsaw. Refine the shape with a sander to ensure a tight friction fit. This collar should be fixed securely to the jig base using glue or nails. It must hold the router firmly, while still allowing for removal if needed.
Drill a small hole at the opposite end of the jig to act as a pivot point. Measure precisely from the edge of the router bit to the intended radius, then drill at that mark. This hole will accept a pin or nail that serves as the centre of the circle. Be sure it’s perpendicular to the base for an accurate rotation.
For better ergonomics, taper the jig’s edges and round off the corners. This makes it easier to maneuver and more comfortable to use. Consider drilling additional pivot holes along the length of the jig to accommodate different circle sizes in the future. A single jig can then serve a wide variety of tasks.
To use the jig, mount the router in place and set the plunge depth. Insert the center pin into the workpiece (or a removable plate if the surface must remain clean), then rotate the jig to cut the circle. Start with shallow passes—about 4 mm deep—to avoid stress on the tool. Repeat with increasing depth as needed.
This simple jig is an invaluable addition to any workshop. It’s cost-effective, easy to make, and adaptable for various project sizes. With careful measurement and smooth routing technique, it provides a professional-quality solution for creating perfect circles in wood—no CNC router necessary.