Quote Originally Posted by GeorgeD View Post
Hi Irving.

Already made a v-wedge pully for a motorI had,will get some batteries for camera tomorrow and post a pic.

Its as you first said half the radius of a given diameter is what I'm trying to achieve so that the pully sits on the rail like a glove fit.
Which unless perfect will either increase friction significantly or will be sloppy in the transverse. A v-shape is easier to achieve, provides a point contact which is the lowest friction, and is self-centering.