X-Y plotter for beginners

A very simple X-Y plotter based on threaded rods is described in
https://www.thingiverse.com/thing:2655181
Linear units based on threaded rods have a very high resolution, but a rather low speed, which is excellent for laser engraving but too slow for drawing.
In contrast, timing belt driven units heave a very high speed, but a substantially lower resolution. But still enough for most applications. Compare the movies in both Things.
This Thing describes a timing belt (type 1140, 6mm wide) based linear unit, also consisting of only two printed parts.
The main section should be rotated 45 degrees along the Z-axis, to make it fit on a standard 20x20cm printer. The slider has to printed with the timing belt slots facing upward. No supports are required.
One central M4 bolt connects two identical units to form an X-Y plotter.
Several holes are present for mounting to a base plate and installing a laser engraver or a pen holder. A timing belt pulley is included which fits very tight t