Quite a long time ago Dominic suggested that we should make a very large marble machine on a CNC router we have access to. It never really went anywhere but the idea came up again recently and I realised I already had all the parts required. Donkey Kong's balls are 20mm diameter, to fake 6mm mdf I just cut 2 sets of 3mm mdf and stuck them together.
I've been telling people that one of the joys of CAM is that if you want a different size you just scale everything to 200% and recut it, so I did just that. This is just Marble Machine 1 scaled to 200% and then recut and it works perfectly.