>
> Hey Tom


Roy Underhill shows how large press screws etc were cut using a paper
> template in one of his books.  Try to find a copy because I think it's sort
> of similar to your project.  I think he was making a a large apple press
> (apple cider press) or something with a 10" or maybe a 12 inch diameter
> cylinder blank of close grained wood.  He was using straight lines to plot
> a even thread pitch which is slightly different to your need of a
> progressive pitch.


Do you need a double pitch?  Do the tracks also have to pitch along the z
> axis to keep the rolling objects inside as they accelerate?   I guess the
> track  would be horizontal at the top and totally vertical at the very
> bottom?  I would make a prototype out of bendy weldable gluable plastic
> board first to work out the bugs.


  Or did I totally misunderstand that?  Are you making a paraboloid bowl
> and shooting the balls down a chute to get them to roll around the walls of
> the bowl on the way to the bottom?

Cheers
Claudio