Fig. 19.
If when the shaft breaks it has not been sprung by the sudden dropping of itself and the pulleys that were on it, a permanent repair can be effected, after correcting the cause of the break, by the use of a regular key-less compression coupling.
If it has been sprung, a new length comes cheapest in the wind-up; and if overload was the original cause of the trouble, only a heavier shaft or a considerable lightening of the load will prevent a repetition.
In Fig. 20 A shows how to drive to make belt weight count in securing extra contact. In B this weight causes a loss of contact. Bearing in mind that B is not only a loss from the normal contact but also a loss of the extra contact that A gives, it will readily be seen how important a power-saving factor the right sort of a drive is—especially on high-speed small-pulley machines, such as dynamos, motors, fans, blowers, etc.
Fig. 20.
A good many electrical concerns mount some of their styles of dynamos and motors (especially the light duty, small size) upon two V-shaped rails, Fig. 21 (the bottom of the motor or dynamo base being V-grooved for the purpose). The machine's weight and the screws A are counted on to keep it in place. If the machine be properly mounted on these rails, as regards screws A in relation to its drive, the screws reinforce the machine's weight in holding it down and also permit a surer adjustment through this steady holding of the machine.
Fig. 21.