OF 900/OF 1010 copying rings

Copying rings for the compact routers, in a wide spread of metric and imperial diameters. The ring sits in the router base and runs against a template; the cutter reproduces the template's shape, offset by half the difference between ring and cutter diameter. That offset is the thing to get right — the template has to be made to allow for it, or the finished part comes out oversize by a predictable and annoying amount.