Tool to find center of a round stock. It was inspired by the StackExchange thread “How to I drill a hole exactly in the center of a circle” where a picture of the inspiring tool is shown.

The design is split into two parts so that it can be layed flat on the printbed.

The split design is a sacrifice made to allow for a metric scale on the top of the part while still allow the part to be printed without overhangs. (I did tried out a “one-part” version which was oriented on the print bed in such a way that there where no overhangs).
This is a major disadvantage when thinking about the square accuracy. To mitigate this issue the tolerance I incorporated is only halve of my usual tolerance in terms of recess between mating surfaces. My usual is a gap of 0.15/0.3mm. This results in 0.075mm gap around the lengthy-rounded alignment protrusion of the snap-fit and a 0.15mm gap for the face which aligns the 45 degree marking edge of the ruler with the main block. The recesses have been incorporated into the main part not into the marker/ruler body.

In regard of improving accuracy I also suggest to glue the parts together and check alignment with an accurate tool (e.g. a triangle ruler from rOtring)

Note: In regard of the drawback of a two-part design: On the other hand, when comparing the square accuracy of a 3D printer against some metal mill-o-turn CNC thingy the tweak ability of the two-part design ain’t a drawback after all

Link to inspiring StackExchange thread: