When placing in position shafts that are to be connected by belts, care should be taken to separate them by a proper distance, so that the belt may be allowed to sag a little when running. No arbitrary rule can be given, as the location is the determining condition, but a general rule may be stated as follows: Where narrow belts are to run over small pulleys, a separation of 15 ft. is a good average, as the belt may then have a sag of about 2 in. For larger belts, the shafts should be placed farther apart, say 20 to 25 ft., and a sag of 3 to 4 in. will be permitted. If possible, shafts should be arranged so that the sag of the belt will increase the arc of contact with the pulley.

Fig. 141. - Oak-Tanned Leather Belting.

If they are not so arranged, the sag will lower the efficiency of the belt.