Drive Belt Quality Concerns

charlese · Post by **charlese** » Fri Aug 29, 2008 2:00 am

Here is a description of a variable speed drive belt. This description is for high powered snowmobiles, but the second section "Belt Component Design" describes the need for stiff resistance to axial force, and describes the make up of the chords in the outer layer. These features were present in the old Shopsmith drive belt.

I have not been able to find any variable speed belts that are about 1/2" X 26" however Shopsmith is now investigating their decision and I have sent out a couple of inquiries. We will have to wait for a company inquiry. I am sure we will get a very comprehensive answer.
http://www.gates.com/brochure.cfm?broch ... on_id=3850

cityslicker2 · Post by **cityslicker2** » Fri Aug 29, 2008 1:32 pm

If someone could add to my education I would appreciate it. I have always been under the impression that all v-belts were designed and sized to transmit drive forces on the sides of the belt that are in contact with a pulley or sheave. Does this change from using a regular pulley to a variable sheave? My only other experience is with older John Deere garden tractors that used a variable sheave drive arrangement to allow varying ground speeds within a certain gear. These worked very much like the Mark V SS system. If you ever had a belt that wore or stretched so the bottom of the v-belt was contacting the sheaves instead of the sides it was time for new belts. Am I right in my understanding or? Thanks Steve

Nick · Post by **Nick** » Fri Aug 29, 2008 4:27 pm

Thank you Steve for bringing up that point, because it gives me a handy segue into the information I've been gathering from power transmission engineers and belt suppliers all day long.

You are correct in thinking that all V-belts transmit forces through their angled sides. The statement "The Gates belt in question was designed for use in fixed pulleys where the pressure is applied to the center of it, not the sides." is incorrect. It is also incorrect that concave sides are "typical of fixed pulley belts." The Gates belt and the original Shopmith belt (made by Goodyear) have an industry-standard "4L" cross-section, i.e. flat sides angled at 38 degrees. And it is incorrect that "bulges on the sides are not normally a problem..." Large inconsistencies in width are almost always a problem for V-Belts of any standard configuration. Because the centers between the pulleys or sheaves are fixed, the belt will ride up when a bulge passes over a pulley, momentarily pulling the belt tighter. This in turn causes vibration and the bearings or bushings to wear prematurely.

The Goodyear belt has a flat or concave top; the Gates belt is convex. The people whom I called told me that, in their opinion, the shape of the top of the belt didn't matter a hill of beans at the speeds and tensions the belt must endure in the Shopsmith drive system.

Perhaps the biggest misconception in this mess is that the belt in question is not suitable for variable-speed power transmission. According to the consulting engineers at Motion Industries and Bearings, Inc. that I talked to, comparing the Shopsmith power transmission to a snowmobile or tractor transmission is apples and oranges. Snowmobile and tractor transmissions are built to transmit anywhere from twenty to hundreds times the horsepower of the Shopsmith drive system. Standard V-belts are more than adequate for variable power transmission in systems of less than 5 horsepower. Chuck could not find 1/2" variable power V-belts on the Internet because there are none. The similarities in construction between the Goodyear V-belt and snowmobile belt are coincidental. Goodyear confines it's reinforcing webbing to a single layer, Gates weaves it throughout the entire thickness of the belt.

The Gates belt is 1/32" unsized from the Goodyear belt. This is partly due to the way is which the two belts are cut. The Goodyear belt has square corners; the Gates people cut a radius for reasons I haven't been able to discover. However, Jim McCann and I pulled ten belts from the bin at random and checked them all thoroughly.They are all within the range of our original specifications. Our conclusion is that Chuck simply got a bad belt (then woke up on the wrong side of bed).

I took the worst of the ten belts we checked and installed it in a Mark V headstock -- it ran fine. This particular belt had variations of up to 0.030" in its width and was right at the limit of our specs. (Most were well within 0.015".) The reason there wasn't more vibration is that in the Shopsmith system, the belt is tensioned by the spring on the motor shaft. The spring allows the motor sheaves to float back and forth very slightly, and this reduces the momentary fluctations in belt tension. The Shopsmith design is actually more forgiving of belts with bulges than fixed-pulley systems.

The width of the belt is actually the least critical measurement in the whole system. Whatever its width -- as long as it's reasonably consitent -- the high-speed adjustment (which you must do after changing a belt) will compensate for the width of the belt. After performing that adjustment, the speed settings on the dial will be just as close as they are with any other belt. In mounting the Gates belts and testing them, the one important problem I found was an ommission in our high-speed adjustment instructions. With the Goodyear belt, we recommend that those of you without tachometers set the stop in the speed changer so the belt is about 1/8" below the rims of the motor sheaves. With the Goodyear belt, this is approximately equal to 5200 RPM. With the Gates belt, the Shopsmith reaches the same speed when the belt is 1/4" from the rim. I will recommend that we tell the customer that information in a special insert to be included with the Gates belts, and I'll also make the required changes/additions to the videos I've produced on that procedure.

Finally, the suppositions that we had changed to a lesser-quality belt to reduce costs were way, way off the beam -- and it was incredibly thoughtless to make them without cause or evidence. The truth of the matter is that Goodyear requires that we order larger quantities than we can presently afford and so we had to turn to another supplier. Gates claims their belts to be superior to Goodyear (naturally) and they are five times the cost of the Goodyear belts.

In short, this was all much ado about almost nothing. If Chuck had simply asked Gail to replace the bad belt, we would have done so. The only good thing that I can see came out of all this catterwallering is the discovery that we need to to update our instructions.

Because there is so much misinformation about belts and groundless suppositions about bean counters in the beginning of this thread, I am not going to leave it up for long. After all, people who come into these subject cold usually only read the first few posts. I will leave it up over the Labor Day weekend so those of you who have been following this goose chase can see where it ends up.

With all good wishes,

cincinnati · Post by **cincinnati** » Fri Aug 29, 2008 5:17 pm

This conversation is getting way over my head. All I can say, when I buy a product, I have to trust the company will give me the best product and service. I was at the open house in Dayton a few weeks ago and Mr. McCann gave us a tour of the factory and the quality control that happens at Shopsmith. I trust what they do will be the best for me. The customer.

johnmccrossen · Post by **johnmccrossen** » Fri Aug 29, 2008 5:55 pm

Thanks Nick, You resolved my concerns about the width differences between the new and old belts and especially cleared up my concern about where the new belt should be riding in the varispeed sheaves at the high speed setting. John McCrossen

Ed in Tampa · Post by **Ed in Tampa** » Fri Aug 29, 2008 8:33 pm

Okay the Gates belt I received from Shopsmith is the correct belt and it won't destroy my machine when I put it on, is that right?
When I do my high speed adjust I should adjust it to be 1/4 inch below my sheave rim instead of th 1/8, is that correct?
And Chuck needs to get a replacement for the bad belt he got, is that correct?

Ed

Nick · Post by **Nick** » Sat Aug 30, 2008 12:37 am

Ed, that's the God's honest truth the best I can put it together from the people I talked to. I'm no expert in power transmission and V-belt design, but I'm a reasonably competent interviewer/researcher/how-to writer. I'm confident enough in what I've written here to say that if you put the V-belt on and your machine blows up, I will come down to Tampa and fix it personally. And that's a promise.

With all good wishes,

judaspre1982 · Post by **judaspre1982** » Sat Aug 30, 2008 1:03 am

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gregf · Post by **gregf** » Sat Aug 30, 2008 9:13 am

cincinnati wrote:I was at the open house in Dayton a few weeks ago and Mr. McCann gave us a tour of the factory and the quality control that happens at Shopsmith. I trust what they do will be the best for me. The customer.

Put me in this category too. Greg

ldh · Post by **ldh** » Sat Aug 30, 2008 11:04 am

I have to agree, but it makes you wonder when the same Gates belt is advertised/available from another source for $3.85.
ldh