a center finder who use Ikea free pencil.
the maximum width of passage is 50 mm but you can change it.
2 holes for the Ikea pencil, one in the center and 1 hole to draw a line 10 mm from the edge.
1 hole for storing pencil.
1 hole for a round magnet.of 10 x 2 mm.
you can modify this object to your needs thanks to the source file Openscad.
2 h 05 min in the Prusa Original normal mode with 0.2 mm layer height.