Summary

Try to flip its switch, it won't let you! :)

All printed parts except for the electronics.

See a video of my machine here: http://youtu.be/b1dG_5Dqf4s

Instructions

get the electronics (I used the parts as described here: http://9x20lathe.blogspot.ch/2010/01/components-and-schematic-for-useless.html)
you'll also find a wiring diagram which works great on the same site
print all the parts. Use a solid wall thickness for the arm and limit the layer height to 0.1mm. The rest can be done efficiently with a layer height of 0.2mm and about 25% infill. Note that I've added "thermal ears" to the parts, these prevent the edges from curling while printing.
remove the thermal ears and the support for the limit button rods (the 2 little rods on the side of the motor block)
use the hinges to fix the lids to the box (I pre-drilled the holes for the screws)
put the motor where it will be fixed and measure the length of the cables (but don't screw the motor in place yet)
solder the cables to the motor and the end button
figure out how to fix your cables on the switch, so that the motor raises the arm after you flip the switch and stops at the end switch after having flipped the switch back. you can test the motor rotation with 2 AA batteries (or even only one)
screw the switch onto the lid and the motor onto the motor block. stick the limit button onto the 2 rods (I put some double sided tape on it to fix it, or use glue)
guide the cables through the cable ring and solder them onto the switch
screw the arm onto the motor wheel and place it onto the motor axe (using a little glue if you want to)
put the batteries in place and close the lid with the switch on it
HAVE FUN

Useless Machine