International projectionist (Jan-Dec 1948)

above the gate or film trap are there foj| the purpose of properly guiding the filiti;|, down past the aperture to the intermit-^ tent sprocket. If these rollers are out of line with the sprocket, the teeth will engage the film perforations off-center. On some projectors these rollers are adjusted by means of a collar and setscrew, while on others there is no regulating device. Certain manufacturers using the latter type rely on the proper centering to be made at the factory. Nevertheless there are times when an adjustment is necessary. It is important that great care be used in lining up the guide rollers with the intermittent sprocket, as damaged perforations will result (Figs. 4 and 5). If these rollers bind, the faces of the rollers will develop ridges which may roughen the edge of the film. It is also well to examine new rollers closely as in some cases they may be received from the factory damaged in transit and have uneven or burred faces against which the edge of the film comes in contact. Friction Takeup — The take-up adjustment should be checked closely from time to time. An excessive pull can always be detected by a "singing" sound made on the film at the takeup sprocket. The sprocket, of course, acts as a holdback or brake and puts a strain on the film, especially when it is started on a reel having a small hub. This is sometimes enough to cause severe damage to the upper edges of the perforations. Fig. 6 shows the sprocket damage resulting from excessive takeup tension. Tension on Upper Magazine Shaft or Spindle — Proper adjustment of the spring tension on the upper magazine shaft or feed spindle is important. If it is set too loosely, the film will come from the feed roll too fast or with a jerky motion. This is especially noticeable if a bent reel is used; this is bad for any film and particularly for film which is in a dried-out condition or badly worn. If the tension be too tight, the effect will ncft be noticeable on a full reel of film, but the tension on the last 50 or 75 feet will be sufficient to cause serious perforation damage when a small hubbed reel is used. It is possible for the film to break under this strain. | Sprocket Idlers — All sprocket idlers must be properly adjusted. If they are set too far from the sprockets, the film may jump out of place and ride over the teeth. If they are set too close, they will ride the film and cause creasing, especialljRton the lower sprocket, which acts as a 'brake on the friction takeup. The small lock nuts on all idler adjusting screws should always be .kept tight. Failure to observe this rule allows the idlers to drop, resulting in creasing and weakening or permanently marking the film. It has been found that the safest distance to set an idler from a sprocket is the thickness of two pices of film. Some manufacturers recommend the thickness of one piece of film, but this is insufficient as the distance between the sprocket and idler is too small to allow the average splice free passage. When properly adjusted, it should be possible to move any idler from side to side without danger of binding against the sprocket teeth. Badly worn idlers mark the film and should Be replaced. Intermittent Film Guide— The intermittent film guide is for the purpose of holding the film snugly against the intermittent sprocket. Filing the openings in the film guide holders is sometimes necessary to insure the proper amount of side clearance for the sprocket teeth. Moving the film guide from side to side while the projector is running will determine whether or not the teeth have sufficient clearance. Figure 7 shows the results of the wearing of the teeth against the wall of the guide, so that sharp edges are developed which cut into the film, especially if the film is improperly guided into the trap. Many projectionists have found it advisable to substitute a slightly lighter film guide holder spring for the stiff one furnished with some of the older projectors. This change reduces the strain and perm'.ts wide or stiff splices to go through with greatly decreased resistance, thus lessening the chance of film breakage. Intermittent Movement — One of the Fig. 4. This guide roller is not adjustable. Spring 2 is designed to hold it snugly against the washer, 1. If improperly aligned, the film perforations will be engaged and off-center, and the head should be returned for adjustment. Fig. 5. This roller may be adjusted by loosening the setscrew in collar 1 and then, after centering, tightening the screw. Care should be taken not to "spring" the shaft. Fig. 6. The teeth of this sprocket have been undercut because the takeup was too tight. Adjustment should be made frequently. FIG. 7. The arrow shows where the teeth have been grooved to a knifelike sharpness by coming in contact with the wall of the film guide. This ruins film. main reasons for picture unsteadiness is an excessive amount of play between the moving parts of the intermittent movement due to wear. Readjustment is made by means of an eccentric bearing, but care must be taken to see that it is not set so tightly that the parts will bind. Some projectors provide for a side adjustment of the intermittent shaft by means of a collar and setscrew. Proper alignment is necessary to insure against the intermittent sprocket striking the film perforations off-center. Excessive wear of the p'n-cross type of intermittent movement results in flat sides on the pins; this causes a slightly quickened pull-down which gives an added strain on the film perforations. On newer models these pins are equipped with rollers insuring smoother operation. Proper Alignment of Upper Magazine— One of the older projectors provides for an adjustment of the top* magazine to allow for its proper alignment. Unless care is taken to see that the magazine is in line, the film coming from the valve rollers will not feed squarely under the idler roller. Improper alignment of this type causes film to crack from the perforations to the edge of the film. This improper alignment also causes film breaks resulting from film with nicked edges and from loose splices coming in direct contact with the side of the valve. Film Loops — Excessively large upper and lower film loops are noisy. Moreover, a large lower loop will allow the film to drag in any oil which may be present below. The film also has a tendency to jump the sprockets: this can take place if idlers are set too far from the sprockets. On the other hand, if the loops are too small, the perforations may be damaged. Film Tracks or Trap Shoes — Many scratches are caused by worn film tracks, or trap shoes as they are known, on one of the projectors. The worn shoes allow the face of the film to scrape against the recessed aperture plate. Such tracks or trap shoes, together with all tension shoes or door pads that show a "wavy" or badly worn-down surface, should be replaced. Fire or Valve Rollers — The valve rollers of both magazines should always (Continued on page 34) 10 INTERNATIONAL PROJECTIONIST • October 1948