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876 HANDBOOK OF PROJECTION FOR
Besides the automatic controlling switch F, is an externally operated fused switch, designed to protect the motor. This switch does not show in Fig. 364, but is indicated at F in the diagram, Fig. 365. The threaded shaft by which the travelling head is controlled is so constructed that in case either one of collars C or D should become loose, the motor will continue to operate until travelling head B reaches the end of the threads, whereupon it will stand idle. This prevents possibility of damage to the machine. Also by means of a mechanical safety clutch, described further along, no damage will be done to the curtain.
On the inside of box F there is a safety arm, which is securely connected with travelling head B, so that in case the automatic switch for any reason does not work at the proper time, an instant later the safety arm throws the switch to open position, and stops the motor, which same cannot be again started until the cause of the trouble is removed.
We therefore see that the machine is pretty well foolproof, as well as very thoroughly automatic, and while we have not actually examined the device, the photograph indicates a rugged and excellent form of construction.
The bearings of the motor are of bronze. Some of them have an oil well and are lubricated by means of oil rings, as per Fig. 148, page 448, while others are lubricated by means of a wick system. These latter have an oil cup on top of the bearing. The chain is a roller chain, the same as those used on motorcycles. The grooves on the drum are worm grooves, which insures the cable winding properly.
MECHANICAL CLUTCH.— The drum is fastened to the shaft, which sprocket H is not, but idles thereon. On the inside of sprocket H is a mechanical clutch, with an adjustment screw, I, Fig. 364, extending from the end of the shaft on which the sprocket runs. By means of adjustment I, sprocket H can be made to move the drum when it is pulling any desired load. The object of the clutch is protection, both to the curtain and to the electrical part of the machine. In case the cables should get caught, or in case collars C and D worked loose and travelling head B was thus allowed to go too far, instead of tearing the curtain or stalling the motor, mechanical clutch H will slip, thus allowing the motor to run without operating the drum.
The base and all the bearings supports are of cast iron, but the drum is aluminum. Travelling head B is of semi-steel, and