Enjoy Daniel de Bruin's wonderfully-produced video of a miniature marble machine being made from a) exactingly precise stuff from the workshop parts drawer, b) a Pruser Mini 3D printer, and c) a lot of patient work with soldering irons, glues and fiddly lengths of wire.
In this video I'm using a ball bearing of only 5mm wide. The track is made of 0.6mm wire. It took me waaaay longer to construct than anticipated, because a small mistake and the ball wouldn't stay on the track. It took me 5 days to shoot, make and edit.
Below, de Bruin offers a more general look at this incredible hobby. You don't need fancy equipment to get started, but you do need a wee soldering iron (I like the TS100 [Amazon] a lot), a variable-speed power drill for the wire-coiling magic, and precision calipers.