TAZ 6 Spool Holder Shaft

I've been using https://www.thingiverse.com/thing:1608830 on my TAZ 6 for a while and it works very well... except... the spool often seems to hangup on the shaft and then go over centre with a loud CLUNK! :-( I even tried a bit of polished 22mm copper pipe as the shaft but that still went CLUNK! as the spool went round.

I don't like machines that make unexpected CLUNK! noises (and having a kilo of filament bouncing on the top of the printer doesn't sound like a great feature) so I designed