I'm really not good at planning things, i usually just start cutting and building, so i put loads of photos to try explain.
Difficulty was quite intense, the bars need to be tuned in using a chromatic tuner, like a guitar tuner, but ABCDEFG.
Basically, when you hollow out the middle of the bar, the sound is deeper and when you make the bar shorter the sound is higher.
The bars are tuned to the same notes as piano keys.... Mechanical Music Digest.com explains this nicely :)
Videos: Just testing it