Pen mount with a spring to prevent smashing the tip of a felt tip pen. Quite useful for pen based circuit board etch resist ;)
Pen mount derived from http://reprap.org/wiki/UniversalPenTouchProbe#Staedtler_Lumocolour_Pen
Had to do quite a bit of post-processing. I had to drill the hole out to let the pen move freely (10mm), hand drill the tip ferrule hole (1.2mm), and clean up the printed threads a little with a file. I used a spring ripped out of a retractable pen behind the marker to maintain a small amount of downward pressure. Could be optimized, but works.
You will need arhimed\'s Flexy Shaft holder for MENDEL http://www.thingiverse.com/thing:1832 to attach this to the X carriage.