Is it an old original belt?

A few pictures would probably help

Did the old belt slip in the same way?

Have you still got it, to compare with the new?

Perhaps these belts need to be "dressed" in some way

I'm only fumbling in the dark btw but toolroom lathes are high end gear.

Sometimes Apprentices weren't allowed anywhere near them

Edited By Ady1 on 19/07/2012 19:19:38

If it's flying straight off the pulley/s they must be very badly misaligned?

Wolfie, If your flat belt has a joiner in it you might take it out of the lathe and lay the joint on a flat surface. Check the two end parts of the belt are in line and not skew to one another, this can cause the belt to run off.

Wolfie,
I don’t think you should think of the handle as the tensioner. It usually is the tension release to let you change the belt from low to high. I would expect there to be some other means of independently rocking that lower shaft sideways to align the belt on the crown of the pulley and set the tension up. The photos from Lathes doesn’t show enough of the support detail to be sure of how its achieved but the screwed rod in the foreground may be the one but only if the assembly has a pivot at the right hand end (motor pulley end). It all looks a bit on the tight side to get at!

Bob D

Hi Wolfie,

the belt should not need to be too tight, as Swarf M. says the pulleys are slightly crowned over the width, you can see that on the picture that Ady put the link to, the larger pulley shows the slight crown. It is that crowning (aka 'barreling' which keeps the belts on the pulleys, it doesn't need to be much in order to work. Too tight is likely to exacerbate the problem of the belt slipping off the pulleys. As Ady also says you will only shorten the life of the bearings on the spindle and motor.

When serving my apprenticeship I worked with a guy I can only call a 'master' turner. He had a lathe which originally ran from overhead shafting. The 'new' electric motor was mounted on a wall bracket and the original drive pulleys on a countershaft drove the lathe. The motor and countershaft were on a platform hinged at the centre, on the wall bracket and the motor was arranged so that it's weight tensioned the belt. My tutor changed speed while the lathe was running by hitting the belt sideways and it would either slip onto the smaller pulley or ride up onto the larger one. It would then move on the countershaft drive pulley until it was aligned. the belt was around 12 foot long when off the machine.

In the days of overhead shafting that was how the speed of your machine was changed. A machinist couldn't stop the whole shafting system just to change speed. The pulleys should be reasonable aligned to work, oil or grease on the pulley shouldn't make much difference unless it is really excessive, these belt systems would become covered in the stuff and leather belts were often dressed with oil to preserve them.

It is possible that your pulley shafts became misaligned when changing the belts, there is usually a method of setting the angle of the motor drive shaft usually a combination of adjusting screw threads or bolts. I'm not sure how this is managed on the S&B but perhaps another owner or Tony at Lathes.co.uk might be able to offer advice or a manual. It is also possible that a a manual is available through the inter-library loan system or stored on a user forum where files can be uploaded.

Good luck,

Terry

Edited By Terryd on 21/07/2012 02:38:54

It'll be an issue with belt tracking, often this is adjust by slight changes in the angle of one or both shafts (effectively adjusting how parallel tir axes are in relation to one another). If the machine has had a lot of use check that the crowning hasn't worn off too.

When I was at Tech in Dunedin in the early 1960s, our work shop was mainly run by line shafting, the old lathes were gear headed, but to stop the drivebelt had to be put over to the loose pully. The only lathe with its own motor was the Chip Master, I think the motor on that was about half of the motor that drove the rest of the workshop. When the school started the workshop was steam powered. Ian S C

Hello.

Just out of curiosity…
When I was a kid (12 or 13 years old) I saw looms in a weaving factory ran from overhead shafting. I could see the belts being cleaned with kind of a shoemakers knife edge (not the cutting surface) and after that a large (50mm diameter) stick made of some material was used against the contact surface of the belt. I remember the material the stick smelled strongly pine resin.

I know this was a regular procedure when the belt fall from the pulley.

Best regards
Dias Costa

Dias,

That's the technique and the process that I used in the 1950's in the fitters shop.

Every machine was driven from the lineshafting up on the ceiling.

The cleaning with a knife was carried out without stopping the drive belts, so much for H&S, there wasn't any in those days.

Len. P.

Edited By The Merry Miller on 27/07/2012 15:37:21

Edited By The Merry Miller on 27/07/2012 15:37:58

Hi Wolfie

A while back I had a Cincinnati horizontal mill that used a flat belt drive. When I got it it had the traditional leather belt with a metal staple type belt joiner. It was noisy, did not track very well and stretchy. The machine was also fitted with a huge semi open frame 5 HP motor. This motor was used to tension the belt by its own weight on a pivot. There was a lot of tension on the belt.

After ringing around I found a supplier (In Melbourne OZ) of a composite belt made from plastic and leather. The Plastic from memory Mylar was about 2 mm thick; bonded to this was leather with a raw looking fine suede finish about the same thickness I gave the supplier the size and they welded the Mylar backing and skived the leather to match making an endless belt. it was about 50mm wide.

I sold the machine last year having used it for quite a few years the belt never stretched or slipped and it was as quiet as a V belt.

The mill did not need dismantling to fit the belt so it was ordered in. however I was told at the time they could weld a belt on the machine if need be for a service charge to save dismantling.

I don't know if these belts are available in the UK but highly recommended. Maybe a member of the forum knows a source.

Cheers

John