For example, if a Ø20 × 10-in. face width sheave runs faster than 1,100 rpm, dynamic balancing is recommended. The result: 1,096 rpm.

When single-plane balancing is insufficient, two-plane balancing corrects weight on two planes on the component axis. (This is not fully dynamic balancing, but partially dynamic balancing.) The areas affected must be separated to effectively produce a two-plane balance as per MPTA guidelines. So, two-plane balancing acts on nonbalanced units of masses that do not lie within a narrow plane. They are distributed along the component length.

Several factors affect total imbalance: The mass of the imbalance source, the distance from rotational center, speed, and the distance between the imbalance cause along the axial length. In general, the longer a component in relation to its diameter, the greater the need for two-plane balancing at a certain speed.

Two-plane balancing is recommended only where the product face width is relatively large and the operational speed relatively fast, or where balance is critical. It is considered optional and must be specifically requested.

Only partial example charts are presented here, but a full technical e-handbook (and software to size belt drives) are available at maskapulleys.com — or call (800) 463-8928.

A newer system for sizing belt drives

When building a new engineering drive or redesigning equipment, there are several approaches to determining the most suitable belt. In one approach, which we present here, adjusted power ratings are used instead of basic ratings. How is this helpful? Basic power ratings are based only on the size of the sheave and drive speed. In the values of the system we present here, length correction and arc correction factors are applied — to adjust the basic power rating to the ratio and center distance. In selection tables here, the adjusted power rating is presented with both correction factors.

Which components are required for a cost-efficient and precise V-belt drive application? To evaluate a selection quickly, follow these steps.

1. Determine drive requirements. How much power do you need to transmit and at what speed?

2. Based on manufacturer ratings, determine the service factor for your particular application.

3. Determine the design horsepower using the formula for it.

4. Based on your results, determine which belt section would be appropriate for your drive with speed-power charts. (Narrow belt sheaves, more compact than classic sheaves, have different ratings.)

5. Determine the ratio of your drive application based on the ratio formula and find the closest value in the drive selection tables for your selected belt section. A center distance is preselected based on the drive size.

6. Find the number of belts required by dividing the design horsepower by the horsepower/belt value in drive selection tables.

7. Verify the validity of this drive by consulting the number of grooves available in these sheave sizes.

8. Determine whether dynamic balancing is needed for each sheave based on the dynamic or two-plane balancing formula. Note that standard face width dimensions can be found in tables.

Several associations provide belt specification guidelines. Those established by the Rubber Manufacturers Association (RMA) are most commonly used. Too, drive selection program software makes this process easier.