Based on an idea from Michael Cox I printed this wonderful gadget.
Link: http://mikesworkshop.weebly.com/laser-centreing-device.html

As additional vitamins you need one of these cheap chinese laser pointers (as shown in above picture), a piece of 8mm threaded rod and a hotend printer nozzle (serves as iris to narrow down the laser beam.

Works perfectly to find centers of punch marks, holes and even large bores - the best centering device I have ever used!

For detailed instructions visit the link