This is my first draft of a fairly straightforward 80mm cable roller that can turn most types of polymer clay or green stuff epoxy into a ribbed cable. Each rib is 0.5mm in width. The maximum width of the cable is rougly 4mm based on the guides on the side.

NOTE: The inner piece is pretty snugg. I recommend sanding both sides of it ever so slightly until you are happy with how it slides back and forth between the guides.

Since this is a work in progress I would love feeddback on how it performs. Let me know if you want wider or ever narrower ribs or if there are other ways of improving on the design.