X-Y plotter/laser engraver for children and directors

Simple things for simple people...

This is a very basic linear unit with only two 3D printed parts per linear drive and two identical units to form a complete x-y plotter.
No limit switches, no timing belts, just a threaded M6 rod and nut, two 6mm rods with one linear bearing each and a ball bearing with 6mm hole.
Press the nut into the opening of the printed part, using a vise.
The speed may not seem to be impressive, but every second, 150 steps are made.
If the sliding tables of two lin