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808 HANDBOOK OF PROJECTION FOR
positive rotating head, the positive nose, the negative feed assembly and the main frame. (B) The arc controller, which is mounted on the back of the lamp house. (C) An adjustable base which permits of moving the lamp up, down, sideways, backward or forward by means of suitable controls located outside the lamphouse. (D) The insulating telescopic rods by means of which the arc controller is connected with the carbon rotating and feed controls.
The function of the positive rotating head A, Fig. 306A which is carried on the ball bearing, enclosed in housing N, Fig. 306A, is to give the positive carbon a rotary motion, and at the same time feed it forward as it burns away at the arc. Rotary motion of the positive head is produced by driving gear U, Fig. 305A, which is connected to and rotated by shaft 22 in the arc control, Fig. 307A. It is connected thereto by the center telescoping rod, as shown in Fig. 305A.
The carbon is fed forward, as it burns away at the arc, by means of two feed rollers, one of which is shown at R, Fig. 305A There is another similar one on the opposite side of the carbon. These rollers are grooved in the center, and present sharp gripping edges to the carbon. They are mounted on separate shafts. One end of each of these shafts is fastened to a block through which passes a screw, T, Fig. 305A, which connects the two together and provides adjustment of the pressure of feed rollers, R, upon the carbon. The two blocks and adjusting screw are plainly shown in Fig. 305 A. The other ends of these shafts are connected by means of a spiral spring, under tension, S, Fig. 305A. This spring, as will be seen, holds the feed rollers R against the sides of the carbon, under pressure which may be regulated by means of adjusting screw, T, Fig. 305A.
The teeth of gears R, besides being held in contact with the carbon, also mesh with a flat spiral groove, or scroll, machined in the face of part, I, Fig. 306A. Part I is loosely journaled upon part A, and if not held by some means, rotates with gears R. The means provided for holding it are by a pawl and ratchet located in the arc control as shown at 25, Fig. 307A. This ratchet acts four times during each revolution of the positive head, thus causing the part I to stop four times also. As soon as part I stops rotating, feed rollers R, which are always rotating about the axis of the carbon, also rotate upon their shafts, thus forcing the carbon forward until part I is released by the action of the pawl in the arc controller, and allowed to rotate with gears R. When scroll I rotates with