Watchmaker's lathe belting advice

Good afternoon everybody,
I own a watchmaker's lathe I seldom use, it was first fitted with a smooth red round (polyurethane?) belt and, from what I remember, I didn't have problem with slippage.
Having to use it again, I found that, with the years, the belts had hardened and they almost immediately broke .
I bought some of the textured green belting available from various sources, but, though the hot melt joints are easier and nicer than the other type, the belt slips soon, offering almost no traction.
I first put this to the profile of the driving pulley (almost a perfect half round) and material (brass), so I tried to modify it to straight converging flanks, in order to have the belt to "wedge" in and improve traction.
Alas nothing changed, trying by hand, the feel of the belt on the pulley is almost as if there was liquid soap on it, probably using steel or aluminum would make little difference.
An idea I had, was coating the throat of the pulley with epoxy and sprinkle some sand over it, but perhaps you can give me some advice about how to overcome the problem with some specific kind of belting material.
Thanks,
Massimo

Edited By Massimo Dalmonte on 02/06/2021 14:18:56

Edited By Massimo Dalmonte on 02/06/2021 14:19:36

Massimo, you can get special spray on sticky BELT DRESSING, plenty on offer, and they say suitable for any belts, so maybe worth a try?

Chris Gunn

Massimo

how much tension are you putting on the belt and what diameter is the material?

i use a lot of 4,5,6mm habiset material on printing finishing equipment and the pulleys are as you describe with no signs of slipping. On a belt set you measure it loosely on the pulleys and then remove 5% then weld up

Is it possible that your belt is too small a dia and only driving on the inside, if you get a belt a tight fit it will be driving on a larger surface area. Just a thought. I use them on UPT and t&c grinder with no problems.

Thanks everybody for the replies; I'll follow your advice, belt dressing spray and smooth round belt are on the way and I'll check the pulley profile (which looks homemade) again.
Actually, the previous belt was 5mm, this one is 4mm and this could explain part of the problem, beside the textured surface and harder material.
About the tension it should be almost right, though the fact that there are two belts running at 90 degrees to a pivoting countershaft complicates things a bit, as tightening one can slacken the other or make the motor belt touch the countershaft structure.
Anyway nothing is impossible, I'll have to make small changes in belts length and countershaft position at a time until right, no improvement in any area is too small to be considered.
Thanks again everybody,
Massimo

try striking a match on jelly.

I'll take the dog out!

Probably not possible but increasing the diameter of the drive and driven pulleys can increase the available grip.

Bernard Towers has the right idea. Increase the diameter of the belting so it rides on the sides of the V and does not touch the radius at the bottom of the groove. That will give plenty off traction.

Yes, I see that the smaller UPT motor pulley seems rather bigger than the one on my lathe ( 1-3/4" against 23 mm), giving an advantage in the resultant grip.

Apart using a slightly bigger diameter belt, another improvement could be using a leather one, previously soaked in neatsfoot oil, which was the best material available, according to Tubal Cain, if I correctly remember .