He told me "

* I use a fairly massive CNC machine to drag a diamond stylus through aluminum alloy at a depths of 20-50 micron.  Had to customize some machine parts and programming to get optically smooth motion.
* It helps to tilt the stylus slightly in the direction of motion and to use a very light-gauge lubricant.  I grind & polish the stylus to a Rouleax-like shape to promote reflectivity.
* Everybody gets the geometry of the stylus motion curves wrong — they're not conic.  You need to solve an ODE that asks for rigid 3D image motion when some part of the optical path (e.g. the plate) moves.
* Lighting should be consistent with whatever assumptions you make in your ODE.  Point-like sources work best; broad-spectrum sources allow diffractive color effects."

Hope this helps