Multiple vee-belt lathe drive

When I commissioned my Willson slant bed I lathe fitted what I understood were matched A section vee-belts of the appropriate length. Chalking a line across the two belts and then running the lathe for a few minutes, however, suggests that one of the pair is getting ahead of the other.

I gather that this phenomenon can make the lathe noisier than if the belts kept in step and that link belting is recommended as a cure.

The phenomenon is perhaps surprising as I would expect both belts to be equally taut on the tight side of the run.

Have others had this problem and have they recommendations about it, including more radical solutions like poly-vee and timing belts, please?

One assumes that all the sheaves are identical in width and angle, but over the years, this may no longer be the case.

The chances are that after a while the "shorter" belts will stretch (since they will have been subjected to slightly greater tension) and all will then take an equal share of the load.

Years ago, owing to a spec error, the "matched" belts supplied from new, were too long for an application, and to keep vehicles on the road, we had to use three belts, that had been intended for single use. (We messed up the Ford spares supply system for a while, by so doing!) There seemed to be no problems with shortening of service life, so presumably, the belts accomodated any slight differences.

So, I would not worry too much, just keep an eye on the tension for a little while.

Howard

One of our machines uses a 10 belt sheave. They go out of sync very quickly but it doesn't affect the operation.

Matched belts still have a tolerance and looking at the web this can be 0.15inches for upto 50+ inch length. So what you are seeing after running is probably this difference times the number of revolutions. Link belting can't be matched there are too many connections to get two anywhere close to the same length. Poly-vee belts are ideal, as they are cut to width from a single belt, just ensure that the pulley shafts stay parallel when adjusting. From your message though I think you are looking for a problem that isn't there, as you didn't say your machine made more noise than a similar machine just that you read that it can be so.

First check for me, if I had a problem, would be to carefully swap the belts over and see what happens then. As above, a ‘few minutes’ could be a lot of revolutions and the difference might be vey small.

I prefer to act on substantiated facts not just merely a ‘suggestion’.

I agree with Howard, not a problem. Hundreds of helicopters use multiple V belts to transmit power from the engine and act as clutches without significant issues. See https://www.atsb.gov.au/media/4120236/ai-2009-038_final.pdf for an interesting investigation (The R22 uses double V belts but otheres use multiple singles or polyvee. Theis service note even gives instructions for gluing down loost strands at the edge of the belt!
http://enstromhelicopter.com/wp-content/uploads/2012/03/SDB0117R2-Drive-Belt.pdf

Most main dealers would be trying to sell you an new alternator belt for you car if they saw that level of dmage.

Robert.

The Willson Slant Bed Gear Head lathe is noisy at the best of time, so a little belt noise should not intrude.

KWIL:

My Willson is indeed noisy, particularly by comparison with the Myford. Any significant noise reduction would therefore be welcome. My only experience of the type is with my own machine and I take some comfort from the thought that mine may be no noisier than the rest!

By belt noise, do you mean the noise directly emanating from the drive? I expect this is minimal but I had in mind possible additional noise from the gears in the headstock. I will try running the lathe with one belt removed to see whether this makes any perceptible difference.

Meantime, my thanks to all those who made helpful comments.