Motography (Jul-Dec 1913)

December 13, 1913 MOTOGRAPHY 435 Motion Picture Making and Exhibiting By John B. Rathbun CHAPTER VI (continued) ONE or more rollers are placed next to the sprocket, which hold the film on the sprocket and in engagement with the teeth. These guide rollers are hinged on a spring bracket so that they may be dropped out of the way when threading the projector, and are also provided with an adjustment by which the distance of the guide roller from the sprocket may be regulated. This roller should be about two thicknesses of film from the face of the sprocket to prevent the film from climbing or jumping over the teeth. If the rollers were to bear the film directly on the sprocket, the film would be likely to climb, especially at the time of a passing patch. All emulsion dust and dirt should be removed from the sprocket as fast as it is deposited, that is, at the end of every run ; if this is not done regularly, the deposit will increase until it reaches and scratches the surface of the film. The teeth of the sprocket should be examined for wear, and if worn or ridged, the entire sprocket should be replaced by a new one to prevent trouble from climbing or jumping. THE INTERMITTENT SPROCKET. The same remarks apply to the care of the intermittent sprocket in regard to dirt or wear, but it should be remembered that even greater care is necessary in the case of the intermittent as it has a more direct influence on the steadiness of the projection. The intermittent pulling of the latter sprocket wears small cuts on the under side of the teeth which cause occasional slips and mis-frames of the film. The dust may be easily removed from the teeth of the sprocket by means of a small stiff tooth brush. Jumping is often caused by accumulations of dust that become packed on the surface by the continual passage of the film. CARE OF THE GATE AND TENSION SPRINGS. The purpose of the gate and tension springs has already been described in this and preceding chapters. In this article we will confine our attention to its care and maintenance. At the top of the gate is a guide roller for feeding the film as it comes from the upper loop so that it does not slip to one side of the springs in passing through the gate. The roller is generally held in position on the spindle with a light coil spring allowing a very small sidewise movement of the film. On some machines this roller is made in two parts. The film now passes between the tension spring of the gate and the aperture plate. The tension springs are one of the most important parts of the machine. Their duties are two in number ; to flatten the film against the aperture-plate, and to keep the film stationary while being projected. The film when being pulled down by the intermittent sprocket always has a tendency to keep moving after the intermittent movement has come to rest. The pressure of the springs overcomes this motion, keeping the film still while being projected, thus insuring a steadier picture on the screen. These springs usually consist of thin strips of hardened steel. To secure an absolutely sharp picture all over the entire screen the film must be absolutely in one plane, or in other words flat against the plate. Film always has a tendency to curl up and the springs must exert enough pressure on the film to straighten it. The springs can be made to bear more tightly against the film by driving the screw on which the gate latch is fastened further in. This in reality brings the whole gate closer to the plate when the gate is closed. This adjustment is not as even as it might be, as the hinged side remains stationary. The spring must be watched for wear, as the film wears long grooves in them, and they should be renewed when in this condition, or the film will not be in one plane as before mentioned. Do not tighten the springs so hard that the machine runs hard, as this will only cause undue wear on them. If the intermittent movement is in correct adjustment the springs will not have to be too tight to obtain a steady picture. Tension springs should be kept clean from any gelatine which may come from the film. This is especially true of new film. Wipe the springs off with a rag that has been dampened in oil. The cooling plate on the front of the gate absorbs all of the heat from the light which does not go through the aperture. This plate being about % of an inch from the gate shields it from the heat, thereby reducing danger from fire. The aperture plate against which the tension springs press the film usually has two tracks on it about the width of the tension springs and slightly elevated above the surface of the plate. In this way the springs press only the edges of the film, or that part on which the sprocket holes are, against the plate. Thus the surface of the film does not touch the plate itself and will not oe scratched up in passing over it. The constant pressure of the tension springs pressing the film against the plate has a tendency to wear the tracks of the plate. Especially when the springs are short a depression is worn on that part of the track on each side of the aperture. When the track becomes worn in this way a new plate should be installed as a sharp focus cannot be obtained with a plate in this condition. THE TAKE-UP. The take-up mechanism rotates the take-up reel on which the film is wound after passing through the gate. A take-up will work satisfactorily if a little attention is given to it occasionally. During the beginning of the reel the take up reel must revolve very much faster than at the end, on account of the size of the reel. For this reason a friction drive is necessary. A belt or a coil spring generally drives the pulley on the take-up from the pulley on the machine. The belt must be kept tight enough to positively pull the reel, but a belt too tight will not work satisfactory, as it will not slip easily when the lower reel is almost full. The belt must be cleaned occasionally as dirt and oil from the machine are liable to get on it. On the Motiograph the flat take-up belt is adjusted by an idler. On the Power's, Edison, and the other machines the spiral spring on the shaft tightens the tension. THE SHUTTER. The shutter is primarily designed to cut off the light from the lens while the film is in motion. It can be seen that for a fraction of a second the illumination will be cut off from the screen. This dark streak across the