Woodworker Extraordinaire, Matthias Wandel, has a web page on his informative site featuring seven incredible marble machines made by Paul Grundbacher.
According to Grundbacher, a native of Switzerland, he usually skips the other design steps and jumps right into working with wood -- mostly ash, maple, and linden (aka basswood) scraps a from a local factory. Why not? It may not be the most efficient design process, but it's not all about efficiency. Sure, many of his failed experiments may end up going into the fireplace, but he spends his time working in the medium he prefers. I admire that.
Grundbacher makes his own dowels using a technique he learned from his father. That's smart, given how warped and out-of-round some store-bought dowels are.
Here is the page on Matthias Wandel's site about Paul Grundbacher's wooden marble machines.
[ Thanks Walter! ]