Antique Engines & Machinery
Leather Belting – Notes and

Reproduced from Loetzer's Hand-book, 9th Edition, 1913



Hot boxes, breaking of pulleys, slipping and breaking of belts, unequal motion of shafting and machinery, and unsatisfactory results generally are so often directly traceable to illy designed and improper belting that the importance of a little practical information leading to well directed application in this line must of necessity at once become apparent to every intelligent reader.

The two sides of a belt are known respectively: one as the flesh side and the other as the grain or hair side. The grain (hair) side is usually the smoothest, while the flesh side, though rougher, is the stringer. The question at once arises as to which of the two is the proper side to run on the pulley. The grain (hair) side should be run on the pulley for the following reasons: The constant strain upon a belt doing duty Haas tendency to crack the grain (hair) side, which tendency increases with age, it is therefore better to crimp the same than to stretch it as the case would be if run out, while the flesh side being the strongest would be subjected to the least friction and wear by running same out, thus preserving the strength of the belt for a much longer period. Again, the belt as well as the pulley adheres best when smooth; the grain (hair) side being the smoother will, of course, adhere better and pull 30 per cent more against the pulley than the flesh side will.

Belts must be kept soft and pliable, but well protected against water and moisture, and should be kept clean and free from accumulations of dust and grease, especially lubrication oil.

A belt of insufficient width for its lead must of necessity be kept very tight to do its work, thus subjecting it to a strain beyond its capacity, thereby reducing its period of life to a minimum, at the same time producing some of the unsatisfactory conditions mentioned above. Whereas, a belt of sufficient width may be run loose, will do its work satisfactory and last much longer.

In locating shafting and machinery it is desirable to so locate the same (countershafts especially) that the belts will run in opposite directions from the line shaft, thus relieving the bearings from a good percentage of the friction otherwise existing if the belts all pulled one way from the line shaft. It is also important that proper distances are maintained, experience having amply proven that short belts, though of proper width, are provokingly given to slipping. If possible, belts running up and down should be run at a slight angle, better results being obtained therefrom.

A speed of 3750 feet of belt motion per minute according to some authorities should be the limit for quick motion belts, while others maintain that a speed of 3000 feet per minute should not be exceeded. The last figure is calculated to be doubly safe, and may be considered a good standard.



To find the transmitting power of a belt, single thickness, the width being given: multiply the diameter of the driving pulley in inches by its number of revolutions per minute, and that product by the width of the belt in inches, and divide by 3300, the quotient will be the horse power transmitted. For double thickness belt divide by 2100.


Driving pulley, 26 inches diameter.
Number of revolutions, 255 per minute.
Width of belt, 3 inches.
Thus, 26 x 255 = 6630 x 3 = 19890 3300 = 6 horse power transmitted by a single belt.
For double belt 19890 2100 = 9 horse power nearly.


To find the required width of a belt to transmit a given horse power, multiply for single belt 3300 by the horse power; next multiply the diameter of the driving pulley in inches by the number of revolutions per minute, then divide the former product by the latter, the quotient will be the required width of belt in inches. For double belt multiply 2100 by the by the horse power instead of 3300 as for a single belt.


Driving pulley, 24 inches diameter.
Number of revolutions, 250 per minute.
Horse power to be transmitted, 10.
Thus for single belt 3300 x 10 = 33000 and 24 x 250 = 6000, then 33000 6000 = 5 inches, required width of belt. For double belt, 2100 x 10 = 21000 6000 = 3 inches, required width of belt.


To find the number of feet of belt contained in a roll, add to the diameter of the roll in inches, the diameter of the hole in center of roll, multiply this sum by the number of coils in roll, then multiply this product by 131. The three figures on the left represent the number of feet in roll.


Roll 37 inches diameter. Hole 4 inches diameter. Number of coils, 84.
Thus, 37 + 4 = 41 x 84 = 3507 x 131 = 459417 or 459 feet of belt in roll.

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