CNC Etch-a-Sketch

What can I say? I've never been able to draw anything with an Etch-a-Sketch. I won this one in a Christmas gift exchange some years ago and hung onto it with the idea that someday I'd CNC it.

The stepper motors are 7.5 degree Airpax steppers I got surplus many years ago. It turns out those mounting ears are actually NEMA 23 compatible so this should work unmodified with "square" steppers as well. The 7.5 degree steps led me to make the most aggressive gear reduction I could fit in the available space. They take me to about 0.15mm (6 mil) steps with half-stepping.

The stepper drivers are L297+L298 almost straight out of the appnote. They're built on a piece of copper clad with a combination of dead-bug and Manhattan prototyping. I bought all the parts years ago and never got around to etching PCBs. Those flyback diodes are ridiculously oversized because I didn't know better.

I chose http://reprap.org/wiki/Teacup_Firmware because of the builtin gcode interpreter. That s