Tim Hatch

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A potential ball chain pulley 17 Jul, 2010

As promised yesterday, I’m experimenting with a new kind of ball-chain pulley. It’s based around the center hub of thermal receipt paper rolls — a throwaway part that I have an excess of at work (and assume is standard world-wide). It has 12 sections, made out of a thin plastic, and and 4.4mm chain fits well if you make notches for the balls to sink into (see photos). I also got some smaller chain to fit, but it makes much weaker contact points on the end grain.

The plastic comes in black, white, and neutral but I don’t yet know what it’s made out of. It’s 79.5mm long, with an outer diameter of 21.6mm and inner diameter of 11.75mm. It’s easily cut with hacksaw and shaved with a hobby knife, and drills somewhat self-center (they avoid the section barriers).

End view of the spool

I’ve tried deforming (making it oblong) by hand, and it springs back; if you put a chair leg on it, it can get permanently out-of-round though. To test out whether the pitch worked out right, I made this jig with hand-drilled holes. The chain slips off occasionally so I’d need to make a hole-drilling jig to get them perfectly aligned along the length before an actual test. I’m still looking for a good way to mount a 5mm-or-so motor shaft on it as well. The wing-nut with some thread locker works well enough on threaded rod.

Chain wrapped around drilled holes