I engraved a crystal paper weight for Jenima today. To create the text I used Blender. First I created a proof for her to approve, then I rotated the text to suit the laser. To get it the right size and position I used 1 Blender unit to 1 mm.
Because the centre of the text is not in the centre of the crystal I created a plane to represent the sides of the cube. The laser was instructed to fire on the edges of this square; the beam bounces off the bevelled edge of the cube and creates no dots.