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Belt Sizer Instructions

1. First determine the size of Belt Cross Section you need. Use one or both of the two methods below:

A. Disconnect the belt from the drive pulley. Buy a fish scale and tie a string to its hook. Tape the other end of the string to the driven pulley (or roller) and wrap it around several times. Then pull on the scale as hard as the motor would ever pull. Read the Maximum Working Tension off the fish scale.

B. If you are moving boxes on a conveyor, select the Cross Section Calculator and use the Working Tension on Roller Conveyor calculator to mathematically determine the belt's Maximum Working Tension. Beware that this calculation is for an ideal environment where a conveyor is moving hard bottomed boxes. If your conveyor is old, in a dirty environment, poorly maintained, and/or moves boxes that have soft bottoms or that rub against the frame, etc., then set the coefficient of friction to 0.1 or larger as you may need a thicker belt. When in doubt, use Method A above with the maximum weight box on the rollers.

Note: 83A durometer (hardness) is preferred because it has the longest flex life. 95% of the belts we sell are 83A. Only use 92A durometer when there is no other option.

Now select your Belt Cross Section and Durometer by finding a number on the Belt Loading Tension Table (directly below the calculator) that is equal to or greater than your Maximum Working Tension.

2. Determine the Minimum Pulley Diameter (MPD) for the selected belt cross section from the Minimum Pulley Diameter Calculator found on the cross Section Calculator page. (Note that for 92A belts you need to multiply the MPD by 1.3). If the diameter of your smallest pulley is substantially smaller then the calculated MPD, then you need a larger pulley.

Alternately, you need a belt cross section that has a smaller MPD. (Note that flat belts have smaller MPD's than other cross sections.)

Alternately, you need to choose a smaller cross section and more than one belt, but realize that the sum of the belts must add up to the maximum working tension.

3. Select the Length Calculator and use any of the four calculators to determine the belt cut length. The final belt size should be expressed like this:

3/16" x 13.5" 83A

belt cross section x cut length  durometer.

4. Select the Tension Calculator and determine the maximum tension that is needed to install the belt. If this tension is so large that it will bend a shaft, then you need to change the percent stretch in 3 above and re-do 4. Alternately, you can use larger shafts on your pulleys.

If there is any doubt about your belt size, please ask Urethane Belt to check your calculations and send you a free sample. Make sure you install it to triple check that the size is correct.

BEWARE: Your motto should be

"Measure twice, cut once"

because if you order an incorrect size, it may not be returnable, or there may be a hefty 50% restocking charge. We do not normally charge for returns if the belt is unused and is a common size, but if it is uncommon, then we cannot resell it, nor can we recycle it because we do not use regrind; so you may end up owning an expensive paper weight.

Before making a substantial purchase, users should test a number of prototype belts under the same conditions in which the belt will be expected to operate.
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