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852 HANDBOOK OF PROJECTION FOR
are now ready to adjust the arc controller. Close the table switch and with the arc controller switch OPEN — the controller not operating, strike the arc in the usual way, and permit it to burn until a crater is COMPLETELY formed. It is imperative that the crater be fully formed before proceeding further, because the voltage across the arc when a new trim is burning, is not the same as it will be when the crater has fully formed.
When crater has formed, with wing nut AL-105, Fig. 315J at rear of main carbon feed screw loose, adjust arc to what you think should be about its proper length. Then immediately tighten up the wing nut and close the arc controller switch, putting the controller into operation, and observe what happens.
If the controller motor starts immediately when you close the switch, slowly turn adjusting thumb screw AC-39, Fig. 315-1 counter-clockwise (screw it out) until the motor stops. Adjusting thumb screw AC-39, Fig. 315-1, is on the side of the controller.
If, on the other hand, the motor does not start when you close the switch, then turn the adjusting thumb screw clockwise, screwing it in, until the motor starts. You thus have a rough adjustment made for the arc gap you have established by hand. If afterward you think it too long or too short, you may change its length at will by means of the adjusting thumb screw, remembering that turning it the way you would turn a nut on a bolt to tighten it (clockwise) has the effect of shortening the arc gap, while the reverse direction lengthens it.
When you have the arc adjustment made correctly, however, LET IT ALONE, unless there seems to be good reason to think you can improve matters by changing the arc length. Don't be continually monkeying with the adjustments.
OPTICAL ALIGNMENT.— The lens and reflector being in place and clean and the lamp being connected, the controller connected and adjusted and the reflector assembly in correct position, we then proceed to make the necessary optical adjustments, as follows: Strike the arc and close the arc controller switch, putting it into operation. Next, by means of track adjusting handle AL-15, Figs. 315J and L, and the reflector adjusting handle, so adjust the distance from light source to reflector that the light beam completely covers the converging lens, without any appreciable overlap. The light