Instant Circle Jig

While working on an upcoming article on different methods to create curved components, I needed to cut a large radius into a base of particle board. Most of the circle-cutting jigs I have around the shop are set for diameters less than 24″. I needed an instant circle jig for around a 23″ radius. It’s easy to do.

Build Your Own

Grab a piece of plywood that’s longer than the radius you need. Because I was using this setup to cut off 1/2″-thick particle board, I used a trim router with a 1/4″ upcut spiral router bit already installed – another setup that we have ready to go in the shop. I didn’t need a plunge base because I was working from edge to edge on the board, not starting somewhere in the middle of the base. Through the plywood drill a 1/2″ hole, which is where the router bit sticks through.

img_0564My router base has a few holes drilled through it because of some other work I’ve done in the past, so the next step is easy, too. Slip the router bit through the 1/2″ hole, try to center it so that it doesn’t touch an edge then drive a couple of screws through small holes in the router base to attach it to the plywood.

img_0565Measuring from the edge of your router bit, lay back the radius amount then drill a through-hole that slips over a pivot point on the particle-board base. I had previously located the pivot while drawing in the needed arc. Slip the instant circle jig over the pivot and slowly make the cut to produce a clean and accurate arc,

img_0568It works every time as long as you have a piece of plywood (or other wood) that’s longer than your radius. And you’re willing to put a couple of holes through your router base.

— Glen D. Huey

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