This section is from the book "Bepler's Handy Manual of Knowledge And Useful Infomation", by David Bepler. Also available from Amazon: Bepler's Handy Manual of Knowledge and Useful Information.
Leather belts must be well protected against water, and even moisture.
India-rubber is the proper substance for belts exposed to the weather, as it does not absorb moisture, and stretch and decay.
Leather belts run with grain side to the pulley will drive 30per cent more than if run with flesh side. The belt, as well as the pulley, adheres best when smooth and the grain side adheres best because it is smoothest. It is desirable to run the grain (hair) side of leather belts on the pulley in order that the strongest part of the belt may be subject to the least wear.
The transmitting power of a double belt is to that of single belt as 10 is to 7. In ordering pulleys the kind of belt to be used should always be specified.
The motion of driving should run with and not against the laps of the belts.
If too great a distance is attempted, the weight of the belt will produce a very heavy sag, drawing so hard on the shaft as to produce great friction in the bearing; while at the same time the belt will have an unsteady, flapping motion, which will destroy both the belt and the machinery.
If possible to avoid it, connected shafts should never be placed one directly over the other as in such case the belt must be kept very tight to do the work. For this purpose belts should be carefully selected of well-stretched leather.
It is desirable that the angle of the belt with the floor should not exceed 45°. It is also desirable to locate the shafting and machinery so that belts should run off from each shaft in opposite directions, as this arrangement will relieve the bearings from the friction that would result when the belts all pull one way on the shaft.
The diameter of the pulleys should be as large as can be admitted.
The pulley should be a little wider than the belt required for the work.
Having properly arranged the machinery for the reception of the belts, the next thing to be determined is the length and width of the belts.
When it is not convenient to measure with the tape-line the length required, apply the following rule: Add the diameter of the two pulleys together, divide the result by 2, and multiply the quotient by 3 1/4, then add this product to twice the distance between the centers of the shafts, and you have the length required.
The width of belt needed depends on three conditions:
1. The tension of the belt. 2. The size of the smaller pulley and the proportion of the surface touched by the belt. 3. The speed of the beit.
The working adhesion of a belt to the pulley will be in proportion both to the number of square inches of belt contact with the surface of the pulley and also to the arc of the circumference of the pulley touched by the belt. This adhesion forms the basis of all right calculation in ascertaining the width of belt necessary to transmit a given horse-power.
The tensile strength of good ox-hide, well tanned, has been carefully examined with the following results:
The solid leather will sustain, per inches of width..675 lbs.
At the rivet-holes of the splices, per inches of width. 382 lbs.
At the lacing, per inches of width...............210 lbs.
Safe-working tension, per inches of width........ 55 lbs.
The belts are assumed to be three-sixteenths of an inch thick.
Pattern-maker's rule should be for
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of an inch per linear foot