While building a gate, I was left with one major task—cutting an arch at the top. The thickness of the wood (8/4 mahogany) demanded a circle-cutting fixture that was very stiff and accurate. So I devised this fixture based on the 8-ft.-long pipe clamps I had used to glue up the gate. It consists of two bar or pipe clamps, a pivot-block assembly, and a router base. The clamp block on the pivot assembly is sized so that the pipes remain parallel from one end to the other.

To cut the arch, I determined the radius and pivot point and clamped the pivot block to the gate at this location. I then clamped the router base to the pipe at the other end and carefully cut the arch by rotating a plunge router through the curve, taking light cuts with multiple passes.

Drawing by Jim Richey.

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