This trick was used as far back as the 19th century to synthesize musical tones. The gears have 24, 27, 30, 32, 36, 40, 45, and 48 teeth, so the notes are all related by simple fractions – that makes this a just intonation scale rather than equal temperament.
There's plans and instructions on thingiverse: http://www.thingiverse.com/thing:6662
A working violin made from maple and oak craft wood. The design is all 90 degree angles except the fingerboard. The tuning pegs are literally square pegs in round holes.
The thing's tuned two half-steps low until it gets used to the tension.
I have never played a violin, so many thanks to Bre Pettis who dusted off his 15-years-neglected fiddling skills to test-drive this violin! (Hey NYC violinists! Want to help test & demo this thing? Contact me.)
I hope to get all the designs uploaded to thingiverse soon – keep an eye on moonmilk.com if you're interested.