The amount of times I have needed a Circle Centre/Center Finder to be honest is not that many, but In the past I had a model makers lathe and I could of used something like this Centre/Center Finder, I'm thinking it could be used as a set square as well on the outer edge.

I wanted a 1 piece component design, something which would print without support and this is the design I came up with.

The slot to scribe has a chamfer so it can take a sharp pencil or fine point pen, there is even a hole to hang the finder on a wall.

The model can be scaled in the slicer if you need a bigger version.

Prints as on the preview face down with no support.

Thanks for looking.