Procedure: Replacement of the winding spool clutch spring on a Realist

The film advance mechanism of a Realist stereo camera has five main parts:

1. A slotted spool to hold the advancing film and which pulls the film through the camera. The spool has a flange on the top end, a slot into which the film tail is placed during film loading, a film-gripping spring within the hollow axis of the spool, and a small hole with an Allen set screw, to lock the spool onto a steel axle through its center, which turns to advance the film.
   
2. A drive axle through the center of the slotted spool. The axle fits through the top of the camera, passes through the clutch mechanism described below, then through the slotted spool and finally slips into a bearing hole in the bottom of the camera. The top of the axle extends above the camera and terminates in a small gear, fixed to the shaft firmly to allow the axle to be turned by the winding knob. When the axle is in place, only the gear at its top is visible. The axle has a flattened spot to bear against the Allen set screw which locks the spool to the axle.
   
3. A knurled winding knob, turning on a machine-screw axle and having a recessed underside. When in place, the knob is not centered on the drive axle described above, but it completely covers the exposed gear of the drive axle. An attached fixed gear within the recessed underside, concentric with the hub of the knob, has teeth facing outward which engage the gear at the top of the drive axle. When the knob is turned, the axle is driven in the opposite direction.
   
4. A tightly wound spring which fits around the drive axle just beneath the camera top, snugging tightly to prevent the axle from turning. Each end of the wire spring is turned outward, forming prongs that may be forced by levers in the direction that tends to unwind the spring. When that happens during film advance or rewind, the axle is freed for turning.
   
5. A clutch release washer, fitted on the axle just below the clutch spring and against the flange of the slotted winding spool. The washer has two protuberances and one groove: the inner rim of the washer is turned upward for about one third of its circumference, forming a boss that fits around part of the clutch spring. The outer rim of the washer has a small turned-up tooth that fits into a hole in a nearby lever, permitting the lever, during film advance, to pull the washer through a slight rotation and slightly unwind the spring. A radial groove extending outward from the inner rim forms a recess to hold one of the prongs of the clutch spring. The other prong of the clutch spring rests against a second lever which, during rewind, forces the spring into a slightly unwound position to allow the drive axle to rotate.
   

Function: The knurled knob turns the axle, which turns the spool, which pulls the film. The spring and washer serve as a lock and release mechanism. The spring grips the axle and prevents it from turning except during film advance and rewind, when the spring's prongs are moved slightly in the direction that tends to unwind the spring, thus freeing the drive axle. The method of loosening the clutch is different for advance and rewind. To advance the film, it is necessary to press the film release button on the back edge of the top camera plate near the rewind knob. The button moves a lever to the left. This clutch lever has a small hole into which the tooth on the outer rim of the clutch release washer has been inserted. The lever pulls on the tooth, causing the washer to rotate slightly. One prong of the clutch spring is lying in the recessed groove of the washer, and as the washer rotates, the prong, caught in the groove, moves with the washer. Since the other end of the clutch spring is resting firmly against another lever, the spring unwinds slightly and allows the axle to turn. As the film advances during the winding, its sprockets pull a sprocket gear through one revolution. Partway into the revolution a cam holds the clutch lever in its leftward position, allowing the operator to release the button. As the revolution ends, the sprocket gear locks in place and the cam releases the lever, allowing the clutch spring to grip the drive axle again. To rewind the film, the advance/rewind disk on the top of the camera must be moved from A to R. This action frees the sprocket gear and allows the film to be pulled backward through the camera into the film cartridge. When the disk is turned to the R position, a rewind lever is also moved slightly to the left. Since the second prong of the clutch spring is resting against the rewind lever, the spring is slightly unwound and the axle is released for the rewind operation. Moving the disk to the A position allows the clutch spring to grip the axle tightly again.

Clutch Spring Replacement: When the clutch spring breaks (usually, one of the prongs breaks off), obtain a replacement spring. Remove the camera back. Remove the knurled winding knob by removing the machine screw that serves as its axle. Remove the Allen set screw in the slotted spool. Pull the steel axle out of the camera by lifting the gear with a small tool, gripping the gear and pulling upward, or by removing the bottom of the camera and pushing the bottom end of the axle out of its bearing hole. Removal of the axle frees the winding spool, the clutch spring and the clutch release washer. Save the broken clutch spring for bragging. Hold the camera upside down. Using tweezers, put the clutch spring in place by putting the longer, hooked prong between the rewind lever and the small cylindrical post on the left. The spring should be centered on the axle hole. Next, put the clutch release washer against the spring, with the second, shorter prong resting in the radial groove. The raised boss should be nestled against the body of the spring. Don't try to put the tooth of the washer into the film advance lever yet. Carefully insert the slotted winding spool, with its flange against the clutch release washer. Now, insert the steel axle up through the hole in the inverted camera, through the spring, washer and spool, and toward the bearing hole in the bottom. At some point, the clutch spring will meet the thick part of the axle, and some force will be needed to push the axle farther. At this point it may be helpful to use tweezers to put the tooth of the clutch release washer into the hole in the film advance lever. If this is done, then turning the advance/rewind disk to R will force the spring slightly open and allow the axle to move into final position. If the axle can be put into position without engaging the tooth and lever, then put the tooth into the lever's hole next. Replace the knurled winding knob. Finally, turn the knob until the flat spot on the axle is aligned with the key hole and replace the Allen set screw in the film advance spool.