Router circle-cutting jig
A trammel jig lets a trim router cut clean circles and arcs by pivoting around a pin. The design is a 300 mm arm 60 mm wide and 8 mm thick that bolts to the router base, with 6 mm pivot holes every 10 mm for radii from 50 to 250 mm, a 35 mm bit clearance hole and counterbores for the base screws. Print it flat in PETG with 5 walls so it resists flexing.
Router base hole patterns vary by brand, which is exactly why a generic file rarely bolts straight on. SpeakCAD lets you specify your screw spacing, bit opening and the radii you cut most, and produces an arm that fits. Refine the length or add a fine adjustment slot in chat before paying for the download.
Design a router trammel arm 300 x 60 x 8 mm with a 35 mm bit clearance hole at one end, three M4 counterbored mounting holes on a 60 mm circle around it, and 6 mm pivot holes every 10 mm from 50 to 250 mm radius.