Canvas belts

Hi all,

I’ve been belting up machines to my lineshaft using canvas belting. I’ve noticed that I’ve had to shorten every belt after a short amount of time. I assume some stretch is common with new belting. Is there a rule of thumb for the tension on canvas belting?

Thanks,

Nathan

You are quite correct about new belt stretching. Flat belts need to be as tight as needed to transmit the power needed, with reason. Getting that done with flat belts can be a challenge if belt length alone provides the tension. A tensioner pulley is a big help. I don’t think I have seen them much on line shafts.
There is not really a rule of thumb I have ever heard.
The longer and heavier the belt, the looser a belt can be run, as the weight of the belt provides the ability to transmit power. If you have ever seen a drive belt on a threshing machine, you will get my meaning.
I added a tensioner pulley on my small planer because I put new leather belting on it with cemented endless splice. Not as easy to change as lacing.

Thanks Kevin,

The belting from the drive pulley on the motor to the drive pulley on then line shaft is a 3” wide 3 ply canvas belt. It’s about 10’ or so center to center. I’ve shortened it twice now and it appears to be holding there. The same 3” 3 plys are running from the line shaft to each counter shaft and they don’t seem to have much trouble either. It’s the 1-1/2” 3 ply belts going from the counter shafts to the machines that seem to loosen and slip the most. Granted all of this is new so maybe they just need a few shortenings and they will be good?

Also is there some kind of gripping agent that’s required? I would rather not but if it’s the generally accepted method to use it then that may solve some of the issues

Thanks again for everyone’s help,

DeSelle said:

Thanks Kevin,

The belting from the drive pulley on the motor to the drive pulley on then line shaft is a 3” wide 3 ply canvas belt. It’s about 10’ or so center to center. I’ve shortened it twice now and it appears to be holding there. The same 3” 3 plys are running from the line shaft to each counter shaft and they don’t seem to have much trouble either. It’s the 1-1/2” 3 ply belts going from the counter shafts to the machines that seem to loosen and slip the most. Granted all of this is new so maybe they just need a few shortenings and they will be good?

Also is there some kind of gripping agent that’s required? I would rather not but if it’s the generally accepted method to use it then that may solve some of the issues

Thanks again for everyone’s help,

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See if you can find a copy of Audel's Millwrights Handbook as there's a lot of great info in there on setting up and maintaining line-shafts.

One thing to also consider is the angle the belt is running at in relation it it's rotation. The belt is usually only transmitting power on one side, like a rope being pulled from the driven pulley to the driving pulley, while the other side is just returning to the driving pulley. All belts work the same way, but modern V-belts don't show it as well since they're under so much tension and have built-in rubber grip. A little bit of sag is expected and ok if the belt is horizontal or running at an angle, but if the belt is vertical with a small driving pulley bellow, you'll lose more power to slackness. If you've ever watched old flat belt machinery at the fair, they show the principals the best (being so large and over distance).

As far as belt dressing, to my understanding it isn't required, but greatly helps. Think of it like the difference between a new rubbery V-belt and and old slick one. There used to be companies that made it commercially, but it seems to me that most shops/millwrights just mixed their own. Lots of different recipes, but the common ingredients were rosin, tallow, pine tar, asphaltum, pumice, castor oil, steam cylinder oil, and, and lots of other stuff, all in different ratios depending on who's experience you were with. The general idea was that you wanted something tacky, that stayed tacky over time, but also flowed and didn't build up in one spot or drip off of stationary pulleys and belts. I made a batch a couple years ago and it's a fun experience. Most recipes require everything to be heated and mixed, before being "cast" into a solid. A good tip I found somewhere was to use old paper towel or toilet paper tubes as a mold as the paper helped hold everything together, but comes apart safely as you rub it on a belt like a crayon.

My plan on my set-up at home is to use sewn leather belts (polyester thread) for everything going over short distances as I find that they'll stretch less, and use webbing belts for the longer distance belts.

Do you run them off when not in use? Not meant to be a cheeky question but I always wonder at pictures of old shops with all the belts on....they can't all have been heated and dry?
Us old farm boys were always told to slacken belts every night?
Richard.

Ruston3w said:

Do you run them off when not in use? Not meant to be a cheeky question but I always wonder at pictures of old shops with all the belts on....they can't all have been heated and dry?
Us old farm boys were always told to slacken belts every night?
Richard.

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I've heard of that being done, but haven't worried about it on the machines I use. It might stretch more over time, but I think going from tight to loose to tight wouldn't help things. Keeping it in regular use would help it from getting stiff and forming to the pulleys, but if it was sitting loose on a shaft, that would still be an issue, probably more so as now it's getting stiff at a tighter radius on the ends. I've seen pictures of old factories that had idle belts hanging loose from active line shafts, tied so they wouldn't cause an accident, but I always understood those to be belts that were simply not in use at the time, such as for a machine being serviced, or a shorter length for an alternate pulley.

I’m glad that question came up as I have been wondering about that as well. I have been leaving them on.