The instructions Pat Warner's router circle jig has pretty much identical instructions for setting the pivot pin to router bit distance - he claims that, with care and experience, the circle diameter can be set within a couple of thousandths. His jig, shown in the attached photo, uses a .185" diameter pin (I believe that this is a section of #13 drill bit) which gives a close but workable fit on a 3/16" drilled hole - you can just make out the pin to the left of the clamp knob. I wish now that I'd thought to ask Pat about making the center hole in the plate for a snug fit on a 3/4" guide bushing - I don't know what the actual hole size is but it's quite a bit larger than the biggest standard size - somewhere in the shop I have a circle guide that I made years ago with a 3/4" center hole; to use, I just mount a 3/4" bushing in the router, drop it in the hole and cut the circle. The router doesn't rotate as you cut the circle and so the power cord doesn't wind itself into a know, no matter how many rotations you make to get to the required depth. Pat's jig is a dream to use, very easy to adjust, and I guess I could modify a guide bushing by shrinking a brass/nylon ring on the OD of a guide bushing and using it that way.
Last edited by tomp913; 10-02-2019 at 06:27 PM.