(Photograph courtesy of Dick Hack.)

Right end view of a revolver magazine with a spring-barrel powered rewind system originally from National piano #348. This loose early revolver was replaced by a more modern late style revolver magazine taken from a junked out National piano. The motivating advantage was to have a magazine with the late torsion spring powered type of rewind system, which, very importantly, made use of the much more convenient interchangeable music roll feed spools. This was the main criteria for making the magazine exchange, to have a National piano in which music rolls could be changed with relative ease, rather than having to manually unspool the old music roll off of the feed spool, and then spool a new music roll onto the now empty feed spool. There are, however, documented pianos with revolver magazines that have spring-barrel-powered rewind systems that are equipped with removable feed spools, but this particular magazine is not one of them, and it is, as of this writing, the only known revolver magazine that does not allow the feed spool to be removed.

The bright brass colored geared spring-barrels are axially positioned (around the revolver magazine) in line with the music roll feed spool shafts, which are indirectly connected to the spring-barrel by means of intermediary gears. Between the feed spool (at left) and the take-up spool (at right) is the coarsely threaded shaft for the feed spool follower. At the far end of each follower shaft can be seen a cast bronze follower, which is used to stop the rewind process when a spring loaded plunger in the follower casting bumps up against a brake lever that pivots and, in turn, forces a length of hardwood dowel up against the left side take-up spool flange. In this photograph the take-up spool for the roll station at picture left has been removed.

(Photograph courtesy of Dick Hack.)

Music roll station for a revolver magazine with a spring-barrel powered rewind system originally from National piano #348. This singled-out roll station is viewed from the right-hand side of the revolver magazine. The geared brass spring-barrel is at lower left. The music roll feed spool is above and also at the left. The take-up spool is on the right side and it is favorably rotated so that the narrow slot for insertion of the music roll leader tab is clearly discernible midway along the length of the spool. Between the two spools is the feed spool follower shaft with its easily seen coarse thread. The cast bronze follower is seated in the stop position at the far end of the follower shaft (and near the top of the photograph).

(Photograph courtesy of Dick Hack.)

Close-up of the feed spool follower for a spring-barrel powered rewind system originally from National piano #348. Here the coarse thread cut into the follower shaft can be clearly appreciated, along with the cutting tool's chatter marks at the bottom of the square cut thread. Near the far end of the follower shaft is the cast bronze feed spool follower, shown here in the rewind stop position. The bulge in the bronze casting (to the left of the threaded hole in the follower) houses a spring loaded steel plunger that, when it makes contact with a brake lever located on the outside of the carrier plate, quickly decelerates and then stops the take-up spool from spinning, terminating the rewind process. The steel plunger consists of a rod that has been machined down to a smaller diameter on a portion of the rod. This reduced diameter is slipped through a stiff compression spring, and then inserted into the bronze casting. The end of the small diameter portion has a small hole drilled from side to side, into which is inserted a small cotter pin to keep the plunger from pushing out or falling out of the bronze casting. A cotter pin is a split metal pin that is secured, after passing through a hole in the part to be attached, by spreading the split ends—named after Dr. Rudolf Cotter, circa 1834.

(Photograph courtesy of Dick Hack.)

Right-hand carrier plate for a spring-barrel powered rewind system originally from National piano #348. The geared brass spring-barrel is at the left. At picture center is the spacer elevated bearing for the feed spool follower shaft. There are two machine screws that attach the bearing to the black colored carrier plate. On the follower shaft there are two gears, (1) a small diameter gear on the front side of the carrier plate (and behind the elevated follower shaft bearing) that meshes with the large gear on the spring-barrel, and (2) a large diameter gear behind the carrier plate that meshes with a small gear on the music roll feed spool. To the right of the feed spool is the take-up spool with a large diameter gear next to the spool end flange. When the tracker bar assembly is lowered onto the music roll a small drive gear, or pinion, engages the large gear on the take-up spool, pulling the music roll forward. As the music roll plays the flat spring inside the spring-barrel is slowly wound up ever tighter, until the rewind phase begins, when the tracker bar framework is raised away from the music roll, which also lifts the take-up spool drive pinion. The moment the take-up spool gears disengage, the spring motor begins releasing its stored up energy by speedily rewinding the music roll, until the feed spool follower bumps up against the brake lever that slows and then stops the take-up spool, terminating the rewind process.

When a music roll is fully rewound, with the feed spool follower in the stop position, there will normally still be some degree of spring tension remaining within the spring-barrel. This is necessary to consistently and reliably get the music roll rewound all the way back to the starting point. If necessary, the amount of remaining spring tension can be adjusted. By removing one of the machine screws that holds the follower shaft bearing in place, and loosening the other, the follower shaft can be moved away from the spring-barrel gear, allowing the spring-barrel to be rotated freely in reference to the feed spool follower shaft. But beware, anyone attempting to do this must do so with extreme caution, and have a firm non-slip grip on the spring-barrel BEFORE the gears disengage, otherwise there is the possibility of run-away damage to the spring-barrel mechanism, along with the risk of severe personal injury.

(Photograph courtesy of Dick Hack.)

Looking down on the gear-train for a spring-barrel powered rewind system originally from National piano #348. Here it can be seen that the gear train for this type of rewind system is quite simple. There is a large diameter gear on the rim of the spring-barrel, and a small diameter gear on the music roll feed spool, along with a set of intermediary gears mounted on the feed spool follower shaft. The mechanical leverage for this gear arrangement suggests some 16 to 20 revolutions of the feed spool for each one revolution of the spring-barrel. Although the spring-barrel and the feed spool are aligned on the same axis, and may look as though they might be mounted on the same shaft, they are not mechanically associated, except through the medium of a single set of intermediary gears.

(Photograph courtesy of Dick Hack.)

Looking into a spring-barrel powered revolver magazine originally from National piano #348. Because one of the take-up spools has been removed from the magazine it becomes easily possible to peer at the usually obscured interior structure. Here the spindly looking, straight spoked, cast iron side-plates can be studied. Below the music roll feed spool (at picture top) is the coarsely square-cut threaded feed spool follower shaft, with its cast bronze follower at the right end of the shaft in the rewind stop position. Slightly to the left of this follower, and just below its follower shaft, is another more distant bronze follower for a different roll station. This one, however, is favorably positioned to partially show the yoked follower extension that rides along a steel guide bar, whose sole purpose is to prevent the follower from rotating as it travels longitudinally along the threaded follower shaft.

(Photograph courtesy of Dick Hack.)

Top view of the feed spool follower in a spring-barrel powered revolver magazine originally from National piano #348. Here the cast bronze follower is in the rewind stop position, with its side-mounted, spring loaded steel plunger butted up tight against the braking lever mounted on the outside surface of the roll station's left side carrier plate. The plunger is little more than a steel rod for which perhaps one-quarter of its length has been machined down to a smaller diameter. This smaller end is then inserted into a stiff compression spring, with this assembly next inserted into a special hole in the follower casting, which is then prevented from falling out of the casting by a cotter pin inserted through the end of the smaller diameter shaft.

In this view it is easy to see the follower plunger extending through a hole in the carrier end plate and bumping up against the brake lever. With a fulcrum in the middle, the other end of the lever pushes against a length of hardwood doweling that acts as a brake when in contact with the outside surface of the take-up spool flange. Note that the take-up spool has two separate brakes, both using hardwood dowels as the brake pad. With the rewind stop brake already described, the other brake is continuous, and is adjustable by means of a machine screw working against a compression spring. This second brake is used to maintain a slight bit of tension on the music roll during the rewind phase, and must be adjusted carefully so that it provides just enough tension to keep the paper from looping and flopping around during rewind, but not enough to drag down and stall the rewind process before the music roll is fully rewound.

(Photograph courtesy of Dick Hack.)

Top view of the left-hand carrier plate for a spring-barrel powered rewind system originally from National piano #348. This view reveals two mechanical functions whose importance can easily be overlooked and/or neglected. The upper spool is the take-up spool, and riding on the outer surface of its left flange is a simple, adjustable friction brake. (The housing and hardwood dowel for the rewind stop brake is hidden behind the adjustable tension brake.) The hollow housing that holds the brake pad has a machine screw at its outer end that is used to adjust the force applied to an internal compression spring, and, in turn, to the brake pad surface. It is critical that the braking force be carefully adjusted, so that the paper is under just enough tension to prevent it from looping and flopping around during the rewind phase. At the same time, the braking force must not be so much that it stalls the rewind process, thereby keeping the music roll from being fully rewound onto the feed spool.

The lower spool is the music roll feed spool, which is not removable, but it can be temporarily disengaged from the rewind gearing, so that it can be freely rotated if and when necessary. The spool rides on a fixed metal pin that extends briefly through the end of the spool. Between the spool and the carrier plate is a light compression spring, that presses against a metal collar that, in turn, rides against the spool flange. This simple arrangement gently keeps the feed spool in the correct position to engage the rewind gears while playing music rolls, but yet still possible for the feed spool to be shifted toward the left, temporarily disengaging it from the intermediary gears, useful when manually unspooling an old music roll and then spooling a new music roll onto the then empty feed spool.

(Photograph courtesy of Dick Hack.)

Left-hand carrier plate for a spring-barrel powered rewind system originally from National piano #348. In the middle of the left carrier plate is the rewind stop brake lever. With its fulcrum in the center, the left end of the brake lever pushes on a hardwood dowel that presses against the outer surface of the take-up spool flange. The other, or right end, is acted upon by the spring loaded plunger in the feed spool follower. When the follower is in its stop position the plunger forces the take-up spool brake to quickly decelerate and then stop the spool, thereby terminating the rewind process. The machine screw adjustment (at the upper left part of the carrier plate) is for the take-up spool paper tensioning brake.

On the outer face of the take-up spool flange two distinct "wear trails" are discernible, made by the hardwood brake pads for the rewind stop brake and the paper tensioning brake. Over many thousands of plays, the brake pads have gradually polished the metal surface, leaving behind circular trails that are clearly defined. There is no braking mechanism for the music roll feed spool.

(Photograph courtesy of Dick Hack.)

Left end view of a revolver magazine with a spring-barrel powered rewind system originally from National piano #348. At the front end of the magazine's central axis is the blue painted locking wheel. Around the periphery of the two reddish colored cast iron side-plates are eight black painted carrier plates that support the left side portion of the spools and rewind system that make up each of the independent roll stations. This view wonderfully demonstrates the overall simplicity of the revolver magazine.