To find the length in a given coil that is closely rolled—Rule: the sum of the diameter of the roll and the eye in inches, multiplied by the number of turns made by the belt, and this product multiplied by the decimal .1309, will equal length of the belt in feet.
Fig. 2661.
The grain or smooth side of the leather is the weakest, as may be readily found by chamfering it to a thin edge, when it will tear like paper, and a great deal more easily than will the flesh side under similar treatment. Again, it will crack much more readily: thus, take a piece of leather and double it close with the grain side outward, and it will crack, as shown in [Fig. 2661] at c, whereas if doubled, however closely, on the flesh side no cracks will appear. If the edge of a clean-cut piece of leather be examined, there will be found extending from the grain side inward a layer of lighter color than the remainder of the belt; and this whole layer is less fibrous and much weaker than the body of the belt, the strongest part of which is on the flesh side. If the grain side is shaved off thin and stretched slightly with the fingers it will exhibit a perfect network of small holes showing where the hair had root. Here, then, we have weakness and excessive liability to crack on the grain side of the leather, and it is obvious that if this side is the outside of the belt, as in [Fig. 2662], at a, the tendency is to stretch and crack it, especially in the case of small pulleys, whereas if the grain side were next to the pulley the tendency would be to compress it, and therefore, rather to prevent either cracking or tearing. Furthermore, very little of the belt’s strength is lost by wearing away its weakest side.
Fig. 2662.
Another and important consideration is, that the grain side will lie closest and have most contact over a given area with the pulley surface.
In making double belts of extra good quality, it is not uncommon to cut away or shave off the grain side of both belts, and place those surfaces together in making up the belts.