Summary

UPDATE: After several test prints I think that this version of the gondola is not as good as previous v3. Somehow the movable mounts lead to less accurate, very curvy angles in the drawings.

This is an enhanced (but slightly more complicated) version of a gondola (penholder) for a simple vertical plotter (like Polargraph, Makelangelo, Drawbot).
This design has movable mountings for the bead chains which create smoother moves and straighter lines compared to v3. You will need some additional M3 bolts and nuts to connect these mountings to the base plattform (see pictures).
The previos v3 does not need any assembly and fewer bolts and nuts. Find v3 here:
http://www.thingiverse.com/thing:472573

See also the bead chain gear in my objects.
http://www.thingiverse.com/thing:467647

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 4 of the gondola. Far from perfect, still a work in progress.
Features:

• Movable mounting arms for bead chains
• Bead chains can be fixed with M3 screws
• Pen can be fixed with M4 screw
• 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)

You can see some more pictures here (text in german, sorry):
http://www.makerblog.at/2014/09/vertikalplotter-im-selbstbau-teil-1-polargraph-kritzler-makelangelo-und-co/