The Moving picture world (November 1926-December 1926)

etter Ppojection ^kis Department Was founxM in. 1910 jby Us frcseni Sditor" ^.KSHch/irdLson Better Projection Pays Motor Heats — Some Reasons FROM John T. Gregory, East St. Louis, 111., comes the following : "I have a show shop in a small city near here. Have a General Electric motor pulling a 70-volt D. C. generator, the output of which supplies the arcs of the projectors. We use sixty amperes and the generator is rated at 100 amperes. It is only overloaded at change-over, which we try to make as short as possible. The generator has lately begun to heat up prettj badly. Can you tell me the reason?" Your data is not very ample, Friend Gregory. The overload at change-over is only 5 per cent., and a G. E motor should carry that without dangerous heating, almost indefinitelj'. We may therefore eliminate overload as the cause. Locate Source of Heat You have given me so little information that I can only tell you the chief reasons for heating. First, you should make a careful test of the parts of the machine to see which heats most, since heat from the faulty part will be rapidly distributed by radiation ■throughout the motor. To do this, bed a thermometer bulb in putty and affix the putty to each part to be tested, permitting it to remain in close contact at least ten minutes. You cannof do this with the rotating parts, of course, but heating in that part is isolated anyhow. How to Find Trouble The heat may be in (a) bearing, (b) The armature, (c) Brushes or commutator, (d) Field magnet, (e) A faulty connection. You may be able to detect the location by sense of touch, of course, or even by smell. I set forth the thermometer test merely for your information, if it seems impossible to locate the seat of heating by other means. Heating of commutator, brushes or armature may be due to too high amperage (not in your case if you are correct in your statement), a "short" between commutator bars or in armature coils. A broken armature coil. Heat communicated from a hoi bearing. Dampness in armature, or electrical disturbances called eddy currents. The latter seems unlikely in your case, however, as the machine has been working, as I understand you, satisfactorily until recently. Exactly What to Do Important : First be sure the machine is really heating too much. Measure the heat in the room with a thermometer, then apply same to machine, as before directed, and if it, the machine, is not more than 80 degrees Fahr. hotter than the surrounding air it is all right. If the heat is in a bearing, the thing to do Bluehook School Question No. 540 — Just why is resistance, or its equivauent, necessary in a projection arc circuit? Question No. 541 — If you have an arc burning normally at 60 amperes and you freeze the carbons, what will happen, find why will it happen? Many Thanks From The Old Man I WANT to most sincerely thank all those hundreds who have sent me cards and tokens on my sixtieth birthday. There was very many — too many of them — to even attempt a personal answer. There is one I just must show you, however. It is from our old friend, John Griffith, and it's pretty nearly a classic. That old feller is chasing me all right, but he's not got me yet, and Nancy Hanks, the Go-Devil, is working fine. Many thanks to you all for your thoughtfulness and kindly remembrance. Somehow, sixty seems a sort of turning point, and I'm really a wee bit tired and will be quite willing to lay down my work and rest when that old chap who is after me finally catches up — but, mind you, he has not got within reaching distance yet, not even for that wicked looking curved cheese knife he carries. is obvious. Put the bearing in good order and use an oil suitable to the work. If the brushes heat too much and their contact with holders and armature is good, then use better brushes. Moisture in the armature acts to partially short-circuit it, thus causing it to heat. Operation at less than normal speed or at over voltage will also heat the armature. If you cannot locate the trouble from what I have said, you had better call in a good motor man. It would require pages to cover this matter fully. Concerning an Aperture Blower JOHN WORTHY, Projectionist, Music Hall Theatre, Pawtucket, R. I., says. "Dear Mr. Richardson : Have been using the Bluebook school since its inception; also have the third and fourth edition of the handbook. "I am now using two Powers Six B projectors, with two American reflector arc lamps in series. Am in a second-run house where most of the film reaches me in verydirty condition. You have mentioned an aperture blower in the department. Please give particulars. "Am working in a non-union house. Maae application to the union and passed examination and investigation. Both committees reported favorably, but I was rejected on final ballot and business agent would not talk to me about it at all. Since I was informed that the books are closed, but they have admitted new members since." I know nothing at all about the reasons for your rejection by the local. But since the privilege of honorably earning your livelihood for yourself and possibly a family at your chosen calling is involved, certainly you were and are entitled to an explanation of the reason for your rejection. That I will publicly say to the local, regardless of whether it pleases them or not, and I have warn» friends in the local too. Answer Is Due Doubtless the reasons for your rejection seemed good and sufficient to the local, but the local OWES it to you, no matter what those reasons may have been, to answer your questions as to the why and wherefore. Such arbitrary actions make enemies, and sometimes bitter enemies too, and often without reason. The foregoing is intended in a kindly spirit to all concerned. As to the blower, you can make one by securing a rubber bulb such as is used on a bicycle horn to a length of small copper pipe — pipe with an outside diameter as small as you can get it, one end of which is closed in with a hammer to form a "nozzle." The other end you may attach to the bulb by soldering it to a larger tube, or in any convenient way. The idea is to make an air syringe and it requires slight ingenuity to work out the method. However, Brother Dobson, Toronto, suggests a dentist's "chip" blower as most excellent for the purpose. My advice is to get a dentist to order one for you. I've never seen one of the dag-nabbed things, but if Dobson says they're all right that goes with tne.