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I was asked to repost this item about approximating the length of a belt that should be used on a belt driven blower assembly. In the figure, R1 and R2 represnet the radius of the drive pulley and the radius of the driven pulley. D represents the center-to-center distance between the two shafts.
Since the belt goes around approximately half of each pulley, the length needed to go around half of each pulley is equal to one-half of the circumference of each pulley, or 0.5(2)(3.14)R1, and 0.5(2)(3.14)R2. This simplifies to
3.14 (R1 + R2)
To this we add twice the center-to-center distance between the pulleys, or 2D.
So, the approximate length of the required belt is about:
2D + 3.14 (R1 + R2)
Consider this example:
Two pulleys with diameters of 4 and 6 inches, with shafts that are 12 inches apart.
The approximate belt length is:
2(12) + 3.14(2 + 3) = 24 + 15.70 = 39.7 inches.
Just to be on the safe side, have a 40" belt on hand, as well as one size up and one size down.