Originally built in January of 2007, the Pin Plotter has undergone several changes.  The current version is capable of producing 1.3 holes per millimeter!

As you can see from the picture on the left, the detail is very good.

The needle (for punching the holes in the paper) is the only non-LEGO part in the model.

The write-up on the website is quite extensive, but there are no CAD directions for building this model.  You’d have to build it based on the photographs.

Technical specifications:

• printable area: 91×70mm (3.6"x2.7")
• maximum resolution: 1.3 holes/mm (33 dpi), using a 0.3mm needle
• time to print a bitmap of about 1,500 holes: some 35-40 minutes
• materials: only LEGO parts (one NXT brick, three NXT motors, three NXT touch-sensors, lots of Technic bricks) except the needle
• software: 14k of NXC commented source
• "printable" media: 105mm-wide paper sheets (best results using 80-100g/mq paper), plastic sheets (not too thick), kitchen "aluminum sheets"…
• NXT brick batteries: 6× 1.2V NiMH AA batteries (rated "2300mAh") allow 100 to 150 minutes printing
• instructions: sorry, I built it by trial-and-error, refining, adjusting, patching… no CAD, no instructions; I hope this page (and photos) may be sufficient to build some similar machine

Read the full article here (in Italian or English).

Thanks to The NXT Step for this find.