Summary

A clock face based on 9's taking a standard clock mechanism.
Printed in one piece from 2 files with a change of filament colour.
Numbers project about 1.5mm from face.

A second version of the base has a sacrificial rim to allow a skirt to be used on the face. See instructions.

A second version of the face has tick marks on the hours.

Instructions

I split this into two parts to make changing filament straightforward.

The first part is just the cylindrical base. It is best to slice this so the motors, heaters are left on, and just moved to a parking position.

Then change the filament and make sure it is extruding the new colour OK. Reset current z-axis position to 0 (e.g G92 Z0) so that next print starts from current height.

Then print clockface. The rim is printed first which gets the filament going without a skirt.

The base is just a very simple OPENSCAD. The face was an image, converted to svg in Inkscape and then extruded in Blender.

Originally I printed both bits without a skirt to avoid the face overlay printing a skirt into fresh air. This meant the first part of the face rim sometimes didn't get going immediately. THis didn't really matter too much.

A better technique which I am now using is to add a sacrificial rim onto the base. With this method I print the base without a skirt and it has a 1mm rim spaced out by 1mm from the main base. The face can now be printed with a 1.5mm skirt which goes on top of the rim and the filament is flowing nicely before the main print starts. The rim is simply discarded after removing the print.

Mathematical Clock