Summary

This is a highly customizable OpenSCAD script to create your own keyring enclosing a coin, that can be configured to allow any coin, o quantity of coins. Text can be configured, as size, font, etc. Once rendered with OpenSCAD the program echoes the heigth at where you have to pause your print to insert the coin, then resume the print to allow the printer to enclose the coin. When measuring your coin, allow some tolerance so your coin drops perfectly into the print. Take also in consideration a vertical tolerance to avoid the nozzle touching the metal of the coin. When you insert the coin in the print, assure it drops below the last layer printed, if not, cancel inmediately the print or you will ruin your nozzle. For more info refer to the ,scad file. An example .STL is included for a 1x1€ european coin.
If you like this, check out my other similar design here: http://www.thingiverse.com/thing:1639203

Enjoy.

UPDATE (23-JUN-2016): Minor changes in code comments.