Crowned pulleys

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Crowned pulleys

Postby Rusty Froe » Tue Apr 26, 2016 9:50 am

I visited Fiddleford Mill a few years ago. The power was transferred around the mill using a series of flat belts around spindles and various gearing mechanisms. The gears had wooden teeth to prevent explosions!

Some of the spindles were crowned (fat in the middle) to stop the belts wandering around. You can find more information on this by searching for information on crowned pulleys (as used on bandsaws and tape recorders.)

I was wondering whether this might have any relevance to bowl turners using straps on mandrels? The effect won't work with string/cord.

If you tapered the end of the mandrel it would stop the strap wandering off.

You couldn't really make a crowned mandrel as all of the turns of the strap would try and overlap each other. You could, however, have a bead in the centre with flares either side. This would only work with two turns of the strap which may not be enough for bowl-work.

Any thoughts? Don't say make one and report back, I haven't finished my poppets yet!
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Re: Crowned pulleys

Postby HughSpencer » Fri Jul 15, 2016 2:35 pm

While the crowned pulleys work well for flat belts on a single loop but I fear the belt would try to ride up onto the next loop around the mandrel.
However, having two crowns, one where the belt enters the loop and one where it exits might keep the belt from wandering off the end of the mandrel. I'm not a bowl expert so would have to go away and test the idea. As a spindle turner I use cord rather than a belt.

Scribbling on a piece of paper, maybe a wide crown with a narrow belt wrapped around it would work. The slope of the crown sides would give a spiral to the belt as it wrapped.

I remember seeing a flat belt 'taken out of gear' by the old chap pushing it off course with the back of his shoulders on a threshing machine. Not something I'd encourage. At agricultural college I did learn how to make up a new flat belt and join it together but I've not had cause to use that skill in the last forty years.
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