View Full Version : Belt progress

J Tiers
07-25-2009, 12:09 AM
Some additional research has pointed out certain things.....

1) the original crowning of the pulleys was still present 60 years later, a sharpish point, with straight sides sloping up to a slight flat at the top in middle of pulley face. There was lots of 'air" under the sides of the belt.

Some flattening and rounding of that pointy crown doesn't harm tracking, but increases breakaway tension somewhat.... however the belting is still pretty stiff, and doesn't like to conform even to a lower crown. There is still "air" under the sides of the belt.

With full contact, I expect I could get where I need. That will take more tension, and I already have quite a bit.

2) Polishing the surface just with a series of files improved the breakaway tension at least 20%. That is good, but I really want about 200% better.

07-25-2009, 03:24 AM
OLD time belt tech, at the driven pulley.
1- The belt has more tension leaving the pulley than approaching.
2- All practical belts have some elastic reaction to loading.
3- The best crown for a particular situation depended on elastic character of the belt and the width of the belt. i.e., for best practical performance and service life, the more stretch resistant a belt was/ is and the wider the belt, the lower the aspect ratio of the crown was required.
4- The wider the belt the less tolerance of abrupt change in linear shear.
i.e. It was/ is well known that wider belts did/ do better with lower aspect ratios of crowing, and they didn't like abrupt conical crowning, so circular and elliptical radius crowning became the "premium" crown.

Some facts behind the above. (Not necessarily in any order)
#1 Assuming some form of slippage will happen and assuming consistency in elasticity of belt (except at a surface laced joint- slappety slap).
The maximum drive effort into the driven pulley happens just as the belt stretch (creep slippage going around the driven pulley) arrives at the elastic extension of the belt on the high tension end of the driving wrap.
i.e., the tension in the belt slowly creeps up as the belt goes around the driven pulley.

#2 It was/ is well know that crowns cause linear shear in the belt.
High aspect and abrupt conical crowns did and can cause belt failure if the belt cannot tolerate the fatigue from said linear shear from said crowning.
The failure was usually one of two ways.
A- the friction surface pealed away from the carcass, or
B- the carcass would tear down the length of the belt.

#3 It was/ is well known that the highest and most consistent friction available surface of any flat belt pulley material (running without additive) was one made of paper stacked so that the belt saw the edge of the paper. (the paper being tightly compressed by tension bolts and compression washers at each end.
Paper pulleys would tolerate oil on the belt too.
I used to have a sample of such a premium pulley, until some AH stole the artifacts in my shed to go to scrap.

#4 The longest lasting, lowest overall cost, and most trouble free pulley was one of iron, (if you could lift it, and if you could keep oil off the belt) and because of the creep in the working belts the smoother surface the better.

#5 I wish Forrest and or Joe Michaels would chime in here. NOT to neglect the other (by cracky) codgers of exposure to old tech where-ever it still existed or exists.

Hope that helps your research. Ag

The Artful Bodger
07-25-2009, 04:54 AM
Agrip, paper pulley eh? We had a Massey Harris tractor (c 1934?) with such a pulley or at least I assume it was. It was something bolted together as you describe and had a remarkable ability to continue driving the hedge cutter machinery even in heavy rain.

J Tiers
07-25-2009, 08:22 AM
#1 Assuming some form of slippage will happen and assuming consistency in elasticity of belt (except at a surface laced joint- slappety slap).
The maximum drive effort into the driven pulley happens just as the belt stretch (creep slippage going around the driven pulley) arrives at the elastic extension of the belt on the high tension end of the driving wrap.
i.e., the tension in the belt slowly creeps up as the belt goes around the driven pulley.

Basically, the belt slips when the creep arrives at the slack side departure point....... and max tension is just before that.

Yes, that is true. Some folks don't believe that, because they think "creep" is the same as slippage, but they evidently have never listened to a rubber belt 'talking" when it is carrying a heavy torque load. Leather seems to be anti-social, it doesn't "talk" much.

The rule of thumb seems to be 20:1 crown for leather, and 40 to 50 : 1 crown for composition. Leather conforms to the surface better, so that all the pulley area is effective.

Even Machinery's Handbook (OLD copy, like #6) is strangely silent about many things to do with belting.

Leather has another property..... like a razor strop, leather in combination with "creep" would keep the pulleys polished and "grippy". Rubber doesn't do that at all, it has no particular tendency to polish the pulley.

The original surface of the pulley was not so smooth at all, and you can easily see the relatively large original crown. At 50:1 it should be only about 0.025:


J Tiers
07-25-2009, 09:48 PM
Polishing further with "wet-or-dry" has produced a bit more breakaway tension, and has changed the character of the slip also.

Prior to this, the slip was "soft", the belt started to "sot of slip" and then finally did slip.

Now, there is plenty of tension right up to the point that the belt DOES slip. It breaks loose with a snappy sound, which I take to mean that adhesion is working.

I will try this for a while, and see how it goes.

I now have some suspicions of the serpentine belts... I don't think they hold one bit better than any other belt. They are usually rather stiff too.

The front side is just rubber, not likely to adhere that much better than any other rubber.

And, the back of most I see is cloth-like, unsuited to a pulley.

Possibly those who use them with ribs towards the pulley get a distinct benefit due to the ribs compressing and allowing the belt to actually contact the entire pulley crown and all, instead of contacting mostly just the middle.

07-25-2009, 11:29 PM

These pages from MHB27 (2004) should be both of interest and assistance:









07-26-2009, 07:52 AM
Serpentine belts might work better with the proper pulleys. I seem to recall John S. using a thread chaser to duplicate the grooves on a pulley. On a flat (really crowned) pulley they probably would not be as effective as a proper flat rubber drive belt.

07-26-2009, 07:58 AM
I am using a Goodyear Gatorback on my SB9 with good results. (No glue) It has angled slots that go across the v's and it is very flexable. A large range of sizes are available,

J Tiers
07-26-2009, 08:17 AM
Tiffie, I see that your MHB has nothing particularly relevant.

None of the 3 copies I have (starting with #6) have anything relevant to this particular issue either. And my Goodyear book on belting applications has nothing on it either.

However, I have satisfied myself that the polished surface has the capability to grip much better than the previous rougher surface. If the pulley is gripped by hand with the belt between hand and pulley, any desired torque can be applied. the heavier the pressure, the better the grip, which was not altogether true previously (and isn't exactly surprising).

So far this is not translating into big improvements in torque transmission, however. I already have the belt about as tight as I can justify, with it at 3% elongation, and "tuned to a note".

07-26-2009, 01:16 PM
A smoother pulley has more surface contact. The only way a rough pulley could do any better is if there were enough tension to actually deform the surface of the belt to conform to the rough surface. I would thing that that much tension would be more apt to wear the belt than to provide any better drive than a smooth pulley. The best thing to study on a flat belt would be to look at the coefficient of friction for various materials and pick the material that would have the coefficient as close to that of the belt as possible.

07-26-2009, 05:12 PM
Most of the leather belt drives I have seen featured dried out and stiff leather that was burnished so smooth it would slip no matter what.Pine tar dressing is what we used.It heated with running friction and became tacky.

The poly-fabric belts aren't made thin enough to wrap around small diameter pullies no matter what you do to them.

This is the stuff if you want performance from a SB or Logan 1" belt drive.

High traction,thin so it conforms to the pullies and crown and endless splicing on the machine.One important feature is low running tension.

Any industrial rubber house can supply it,I get mine from Applied Industrial.


J Tiers
07-26-2009, 07:41 PM
Those look nice, but are just as thick as the one I am using..... between 0.1 and 0.125 inch.... At least for the 30 and 45 lb versions.


07-26-2009, 08:04 PM
They make thinner,.068" IIRC,good for about 1-1/2hp per inch width @ 400sfpm.

J Tiers
07-26-2009, 08:33 PM
That would be about 125 lb effective tension.

I can't locate a type on their site with that tension capability and 0.068 thick....

Can you point me to it?

of course I don't know what the max elongation is either. The 1% elongation pull may not be the most it takes.