One problem, in the timeframe i had it was impossible to get the 9.5mm ballbarings so i had to use "normal" 16 mm marbels.
For this to work i had to change the design. It worked out quite well. The Original design had metal axis i changed it to wood. My modifications are based on 4mm wood (ply or MDF) You can download my modifications to the plans download
Wooden handle and axis, this is the biggest difference from the Original design's by MSRaynsford other modifications are a extra layer in the main gear and some bigger holes (for the marbles)