Vertical Plotter Gondola v3 (aka Polargraph)

My version of a gondola (penholder) for a simple vertical plotter. See also the bead chain gear in my objects.
http://www.thingiverse.com/thing:467647

There is also a slightly more complicated v4 here:
http://www.thingiverse.com/thing:478346

These models (and some electronic stuff) are all you need to build your own vertical plotter. Sandy Nobles (creator of Polargraph) great Instructables is a good point to start:
http://www.instructables.com/id/Polargraph-Drawing-Machine/?ALLSTEPS

This is iteration 3 of the gondola. Far from perfect, still a work in progress.
Features:

Bead chains can be fixed with M3 bolts
Pen can be fixed with M4 bolt
Enough place to glue servo for pen lift
M3 hole for counterweight at the bottom (M5 would be better, could use M5 nuts then as weight)