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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 Minimum Tangential Force Needed off the fish scale.

B. If you are moving boxes on a conveyor, select the Cross Section Calculator and use the Force needed to Rotate Conveyor Roller calculator to determine the belt's Minimum Tangential Force Needed. 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, has heavy or long rollers, 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 go to our Cross Section Calculator and 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 Minimum Tangential Force Needed.

2. Determine the Minimum Pulley Diameter (MPD) for the selected belt cross section from the Minimum Pulley Diameter Calculator found on our Cross Section Calculator. (Note that for 92A belts you need to multiply the MPD by 1.3. For 70A durometer belts multiply the MPD by 0.8). 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 minimum tanginetial force needed.

3. Select our Length Calculator and use any of the four calculators to determine the belt cut length. Note that a table of recommended belt stretch factors is found in Method Two. The final belt size should be described like this*:

3/16" x 13.5" 83A

belt cross section x cut length  durometer

(Flat belts use:  thickness x width x cut length  durometer)

4. Select our 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 DuraBelt 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 new, unused and is a common size, but if it is old, used or 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.

IMPORTANT!
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.


*In order to prevent confusion and eliminate errors, we require that purchase orders either describe the belt (as shown above) or use our part number.  POs that specify only a customer’s part numbers and/or drawings do so at their own risk, and we shall not be responsible for our misinterpretations or errors resulting therefrom.  In the event that a part number and/or drawing conflict with the description, the description shall prevail.  POs that specify a length by anything other than cut length (also called pitch circumference or net endless length) and do not indicate that it is a diameter, ID, OD, IC,or OC, shall be deemed to have specified the cut length.

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