The Moving picture world (January 1926-February 1926)

418 Moving Picture World January. 30. 1926 Sixteen Years of Service to Projectionists where the sprocket is EX.ACTLY ready to start and EXACTLY ready to stop. Inaccuracy here will spoil it all. A moment of consideration will show you that you now have the exact record of your intermittent ratio of movement recorded on the rim of the flywheel, but it is of slight use tiicre. It must be accurately measured, ^vhich would be a rather difficult thing to do while it is on the wheel, unless one happens to have a protractor of the right curvature. We must therefore remove it from the wheel, as follows : cut a strip of tough white paper — writing paper will be best — half an inch or a bit less in width, and long enough to go around the face of the flywheel, with an inch or so to lap. Do Not Cover Scratch Marks Made Lay this paper around the face of the flywheel in such a manner that the edge of the I'aper will come into contact with but not cover the scratch marks you have made. I >ay "not cover" them because the marks may be made either on the side or the face of tlie wheel, and if on tiie face the paper band might be so placed as to cover them. Having got the paper band in place, put a drop of paste on the end which over-laps, press it down and let it dry. You now have the face of the wheel incased in a paper band. Next make marks on the paper PRECISELY opposite marks B and C and, having done so, draw a sharp knife blade squarely across the paper EXACTLY at one of the marks you have made (.either one) severing the paper and removing it from the wheel. At the bottom of the drawing you will see the paper as it will appear after removal. It is a strip of paper on which is one mark, which will be mark B or C, according to which one you cut through. The short end represents the time or period in the picture cycle during which tlie intermittent sprocket, and therefore the film, is in movement. The long end represents the time or period of the picture cycle during which the intermittent sprocket, hence the film, is at rest. The ratio one bears to the other is the "ratio of movement" of the intermittent. Measure Total Length of Paper in Inches You may now transpose these measures into ratios in either one of two or three ways. First, measure the exact total length of the paper in inches, and multiply it by one tliousand (I,0O0) to reduce the measurement to thousandths of an inch. Divide this by 360 and you have the exact width of one degree at the face of your Hywhecl, in thousandths of an inch. Next, measure the exact length from the mark to eihter end of the paper and multiply each of the results by one thousand (1,000), to reduce the measurements to thousandths of an inch. Yon now have all the measurements in lliousandths of an incli and may ascertain exactly what either the period of movement or the period of rest represents in degrees by dividing each of them by the width of one degree. CAUTION: In doing this you cannot use a yard stick or a two foot square. You must make all measurements with GRE.'\T ACCURACY. To illustrate : Suppose our wheel measures 10.99 inches in circumference. 10.99 x 1,000 10,990, and 10,990 360 (degrees in any circle) equals M).5277777J plus, which is where the value of tlie reducing to thousandths of an inch corner ill, loi we find that the width of one degree is 30.52777777 plus thousandths of an inch, and by discarding all but the 30.5 we simplify matters, ;-nd have thrown out only an Infinitesimal fraction of one one-thousandth of an inch. True, even that will affect the result, but only very slightly. YolJ may use 30.52 if you think best, or even as many of the sevens as you care to. We now have the width of one degree in thousandths of an inch and the measurement (if rest and movement of the sprocket in thousandths of an inch, so it is of course only necessary to divide either measurement by the width of one degree to find out exactly how many degrees it represents, or you may divide on. of them and subtract the result from 360 to find the otlier. Another Method of Measuring Another less accurate method is to measure the distance of the mar'< from either end of the paper and see how many times the lesser is contained into the greater, which lells you there is so many times more rest period than there is movement. Still another is to caliper the distance from the mark to th; end of the paper it is nearest to, and tlien, using the caliper, see how many times greater the long end is. But, after all, the degree method is the only real one. I trust this will serve your purpose, friend .Arlington. Note : Gray has called my attention to the fact that it would be difficult to place a pai)er band on a Simplex flywheel because of its closeness to the casing. That is true so here is another plan : Instead of the paper l>and, before you start to put the marks on the wheel, cut a circle of stiff writing paper the diameter of the flywheel. Cut a hole in its center large enough to accommodate the lull) and shaft, and then, with a bit of shellac or paste, attach it to the rim of the wiieel and instead of making marks B and C directly upon the wheel, make them on the paper. When you have finished, remove the paper from the wheel. It will look like the accompanying cut. If you have a protractor you may now measure the distance between marks B and C directly, in degrees. If you liave no protractor you can get one for a small sum at any dealer in draftsmen's sup plies, or if iliere be no such dealer in your town, then you probably can get one at your stationery store, or they can order one for you. Get a small one. On the paper disc, D is the center, corre--.ponding to the center of the flywheel shart. B and C are the marks indicating movement 'if intermittent sprocket. Broken lines Y X may be added if the protractor you have, or ;et, has, as it probably will have, no*, the same curvature as the wheel. To use the iirotractor (which is merely a brass half circle with a center mark and the degrees mr.rked < n its outer, curved edge), place the center mark (found in center of cross bar near lower edge thereof) exactly over center mark i'y. You will have to lay the paper disc on a other sheet of paper, attaching it thereto by means of a bit of paste, and re-locate center mark D, since you have cut away the ceiiter in putting the disc on the wheel. Placing I he protractor center mark EXACTLY over center mark D, you have, but to note the number of degrees between marks B and C, 'iT lines X and Y (exactly the same thing) to know the number of degrees through which the intermittent sprocket (and film) are in movement, and by subtracting that number from 360 you will also have the number of degrees through which the sprocket (and film) are at rest. Simple, what? Of course if you have no protractor ai'.d don't care to get one, then it will be difficult to accurately measure curved line B C, and you had bel.er try to work the paper band ■^tiint. Ficture Weaves WP. JACKSON, Astoria, Long Island, wants to know what wOuld • cause a weaving effect in the picture. The mere statement that the picture "weaves," is entirely insufficient to enable •he B"\ng of an intelligent answer to the particular case. However, if the "weave' merely is an up and down movement, which occurs regularly four times to each revolution of the projector mechanism crankshaft, then either the intermittent sprocket shaft is bent slightly, or the sprocket itself is out of true, due probably to not fitting the shaft snugly. If the movement be both up and down and sidowise, and four times to each revolution of the crankshaft, then the intermittent sprocket is out of true, and one end, or possibly both, "wobbles" slightly. This may be because it did not fit the shaft in the first place, which is quite possible, and quite often the case where "economical" (?????) managers purchase parts made by other than the projector manufacturer, because they are a bit "cheaper" in first cost — and usually a d — ■ d sight more expensive in •he long run. It may also be because it was driven on the shaft, and in the process put under such stress that it was warped out of shape. If friend Jackson will describe the effect very carefully, including information as to whether or not it occurs with both projectors, or only with one, then I possibly will lie able to tell him exactly what is wron^.