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N_Cook N_Cook is offline
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Default Flat belt mechanics

Wild_Bill wrote in message
I don't know what the simple explanation is, but flat belts will typically
self-center on a crown or high spot on a wheel, spindle etc.

This same crown effect is used on many machines, not just tape drive
mechnisms, where they're often seen in electronic repair, but as you

not usually made up of flat angles.


"N_Cook" wrote in message
I don't remember seeing this before. Instead of baluster/bulbous pulley

capstan, two angled faces with a thin ridge in the centre on the drive
pinion. So the belt must ride on the ridge but why does it not hunt

There is a limiting flange either side of the angled flats and the width
the rubber band is greater than the distance between a flange and the
central ridge, but still why no riding about?. Then what I thought was
construction is probably part of the dynamics. The capstan is 2 discs
together but one is 49.94mm diameter and the other 50.04mm so this step
change must make sure the band rides over the ridge but biased to one
lightly touching one angled face, but not touching a limiting flange.

get the mechanism working again I will try viewing with a xenon strobe
. Anyone any input on this ? more or less prone to changes in rubber
restitution/stretch etc, more/less likely to come of when PTO is

greater/less accuracy in speed of drive with varying driven-side back

I just looked in my box of salveage motor spindle pinions, perhaps 30 are
bulbous but no flatted/double-cone ones with this central ridge in there
I always assumed the curvature of a bulbous pinion was something a bit
tighter than the natural curve of the original flat belt if pressured in the
centre only. So if a ridge rather than a soft curved high spot then perhaps
functionally much the same.
While at it , IIRC bulbous edged capstan and flat drive pinion or bulbous
pinion and flat edged capstan, never both bulbous or you will get a hunting
effect coming in