A while back I asked for advice here about routing with a trammel setup. I finally got around to doing it and I'm pleased to say it worked out very smoothly.

My goal was an arc that was 35" wide and had a rise at the midpoint of 4.5".. SketchUp made this child's play to figure out. Simply drawing the curve and right-clicking on it got me the radius (36-9/32") with no calculations.

But then I had to implement it, of course. That went well also. I made marks on my 1x12 oak 35" apart and a mark 4.5" inches in from the edge at the center of what would be the arc. I then turned the trammel upside down and measured along the center line 36-9/32" from the edge of the router bit and marked the spot for the pivot pin.

I intended to use a 10 penny nail for the pin, but it fit just slightly loosely in the hole I drilled. This probably would have made almost no difference, but I found another item that fit the hole perfectly - the drill bit itself. The smooth shank, of course.

I made 5 or six passes, using the stepped dial on my plunge router to set the depth for each pass. In the end, the curve passed exactly through the marks I had made originally. Success!

Thanks to all who offered advice.

Greg