Flat belt mechanics

[N_Cook]

I don't remember seeing this before. Instead of baluster/bulbous pulley or
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 about?
There is a limiting flange either side of the angled flats and the width of
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 crude
construction is probably part of the dynamics. The capstan is 2 discs fitted
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 side,
lightly touching one angled face, but not touching a limiting flange. When I
get the mechanism working again I will try viewing with a xenon strobe light
. 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 engaged,
greater/less accuracy in speed of drive with varying driven-side back torque
etc.

[Wild_Bill]

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 mention
not usually made up of flat angles.

--
Cheers,
WB
.............


"N_Cook" <div...@tcp.co.uk> wrote in message
news:j9vr3g$ipk$1...@dont-email.me...

[N_Cook]

Wild_Bill <wb_wi...@XSPAMyahoo.com> wrote in message
news:icNwq.81438$1x3....@en-nntp-16.dc1.easynews.com...

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

[Gareth Magennis]

"N_Cook" <div...@tcp.co.uk> wrote in message
news:j9vr3g$ipk$1...@dont-email.me...

Thats just reminded me of the DAF Variomatic automatic gearbox.
Here's one working on Youtube.

http://www.google.co.uk/search?hl=en&biw=1024&bih=571&q=daf+variomatic+transmission&oq=daf+variomatic+transmission&aq=f&aqi=g1&aql=&gs_sm=e&gs_upl=23719l28672l0l28922l27l21l0l13l13l0l297l1359l2-5l5l0


Gareth.

[Gareth Magennis]

"Gareth Magennis" <sound....@btconnect.com> wrote in message
news:gLCdnVBac4SgJF7T...@bt.com...

Oops, wrong link. This one works:

http://www.youtube.com/watch?v=mEK4IVhLqL8


Gareth.

[Ron]

At one time Philips washing machines used a very similar system.

Ron

[N_Cook]

Useful to remember if no machine shop available for making a bulbous pulley,
if faced with replacing a motor and its the wrong speed range so forced
change of pulley , or smaller spindle diameter. Except the ridge is
semi-circular profile here and bodge job would be chamfered edges but
starting from a brass rod it would be a lot easier to fashion leaving
central ridge, bodging 2 cone segments and 2 end faces , than fully bulbous
without a lathe

[Gareth Magennis]

"Ron" <r...@lunevalleyaudio.com> wrote in message
news:Ufqdne-ZBIFuWl7T...@bt.com...

Well I'll go to the foot of our stairs!



Gareth.

[Ron]

Aye lad, they used a plastic[1] pulley containing three ball bearings
fert centrifugal whatnot. If the drum got jammed, the belt would slip,
the pulley would burn and emit the smell most horrible.


[1] Looked like Bakelite but probably wasn't

Ron

[N_Cook]

Ron <r...@lunevalleyaudio.com> wrote in message

news:LredneToxo3ETl7T...@bt.com...

Dyson vacuum cleaners have a similar mechanism. An unnecessary football
rattle mechanism in the slip clutch so a disturbingly nasty noise on a jam.
Incidently anyone else find the phrase "No loss of suction" for a system
that forces air down draggy 10 foot of narrow piping, inside the machine,
unlike conventional ones- air in and out over 1 foot if that.

[N_Cook]

N_Cook <div...@tcp.co.uk> wrote in message

news:ja0is8$qre$1...@dont-email.me...

Back working with a silicone rubber flat belt, shame it is bright orange.
Looking under x30 the original band had a furrow along its centre. I've
since found a salvaged variant on this pinion , 2 angled cones with an
included angle of about 110 degrees but no ridge , just a rounded join
probably about .5mm diameter again. The band cannot deflect that much so
must ride on that central edge, like the one I just fixed. Perhaps bulbous
ones are just kinder on the rubber