(Photograph courtesy of Dana Johnson.)

Fully loaded revolver magazine in a typical National coin piano (serial number unknown). This revolver magazine is of the torsion spring powered rewind system type, and consists of a center shaft on which is attached (from left to right): (1) a notched locking wheel, (2) a chain sprocket used to synchronize the tune selector wheel, (3) the left side cast iron revolver flange, (4) the right side cast iron revolver flange, (5) a sheet metal belt pulley used to rotate the revolver magazine, and (6) a chain sprocket used to synchronize the studded cylinder in the coin switch mechanism with the rotational position of the revolver magazine. Attached to the outer rim of the cast iron revolver flanges are eight self-contained music roll stations.

The notched locking wheel (at left on the center shaft) is used to lock and align the revolver magazine, so that a music roll station perfectly lines up with the tracker bar during the Play operation. Above the locking wheel is the bronze locking hook, which consists of a lever arm that pivots on a bearing pin at the rear end and with a specially shaped hook on the front end. About midway on the locking hook lever is a vertical rod that connects with the tracker bar frame. In this photograph the tracker bar frame (not visible) is in the raised Rewind/Roll Changing mode position. Thus, the locking hook is not pushed down into a locking wheel notch, leaving the revolver magazine free to rotate.

At the left side base of each roll station, near where it attaches to the outer rim of the revolver flange, is a long brass lever that is a little longer than the station is wide. This is the release lever for the take-up spool follower. The upper end of this lever rests over the end of a steel rod located behind the take-up spool, which, when the lever is pressed inward, disengages the gear that drives the take-up spool follower. This release lever will be needed whenever a music roll is loaded or unloaded from the revolver magazine.

(Photograph courtesy of Dana Johnson.)

Left side of revolver magazine in National piano #7173. On the center shaft, at left, is the locking wheel. Directly above it is the bronze locking hook, which pivots on a pin at its far end. Midway is an eyelet protruding to the right, into which is placed a vertical metal rod with a threaded end, the upper end of which is connected to the tracker bar frame. A pair of hex nuts on the rod are used to adjust the hook position relative to the locking wheel. To the right of the locking wheel is the chain sprocket used to synchronize the revolver magazine with the tune indicator wheel.

Further to the right, and at the base of the roll station attachment plate, is the release lever for the take-up spool follower, which is clearly defined in this photograph. At its lower end is an adjustment screw that enables the upper end of the lever to be precisely positioned, and to eliminate any lost motion between the lever and the wire rod it snugs up against. About a quarter of the way up the lever is a brass pivot bearing, which allows the lever to rock in or out. When pressed inward toward its upper end, it pushes on the rod running behind the take-up spool and disengages the gearing for the take-up spool follower.

(Photograph courtesy of Dana Johnson.)

Empty revolver magazine in National piano #7274. On the right side of the revolver magazine is a 12" diameter sheet metal belt pulley, which is constructed of two identically stamped sheet metal halves held tight with a central metal hub. It is used to rotate the revolver magazine when the player system is in the Rewind/Roll Changing mode. To the right of the belt pulley is the chain sprocket used to synchronize the revolver position with the studded cylinder in the coin switch enclosure. Notice that the lower take-up spool is perfectly positioned to show the narrow slit into which is inserted the paper tab on a tapered music roll leader. An empty music roll spool is seen below the take-up spool.

Focusing on the roll station centered in the photograph, notice the horizontal shaft and coiled torsion spring located just below the take-up spool, and that goes the entire width of the roll station. The spring is secured to the shaft bearing on the left side roll station plate, and to the shaft near its right end. This torsion spring is gradually wound ever tighter when the music roll is played, and then, when the Rewind/Roll Changing mode is triggered, it supplies the motive power to rewind the music roll. There is a large diameter gear on the torsion spring shaft that interacts with a small diameter gear on the feed spool chuck. Below the torsion spring is yet another interconnected shaft for the feed spool follower. This follower shaft is threaded and has a small diameter gear on the right end that also meshes with the larger diameter gear on the torsion spring shaft.

Both follower shaft and the feed spool shaft have gears of equal size, and so both shafts rotate at the same speed. At the left end of the follower shaft is a stiff compression spring, which acts as a bumper stop for the spool follower located immediately to the right of the spring. The spool follower is a simple yoke with a threaded hole through the base end, with the yoke over a stationary rod that keeps the follower from rotating on the threaded rod. Because the follower cannot rotate, as the shaft is turned the follower moves sideways on the threaded rod, following the relative rotational position of the music roll as it is played. Once the roll begins rewinding the follower will move horizontally to the left, eventually contacting the bumper stop spring and then brake the feed spool's rewind motion.

(Photograph courtesy of Dana Johnson.)

Closeup of empty roll station in National piano #7274. Here the torsion spring rewind shaft and the feed spool follower with its threaded shaft are more easily studied. Notice that the threads on the feed spool follower shaft are only cut perhaps a little more than 2/3 the length of the shaft, which is understandable in that the feed spool follower shaft rotates at the same speed as the feed spool itself, and so there is plenty of thread length for a single tune music roll. Now drop down to the top area of the lower roll station (just above and to the rear of the take-up spool), where there is the spool follower for the take-up spool. Almost the entire rod is threaded, and for good reason. The follower shaft has a small diameter gear on it that meshes with the large diameter drive gear on the take-up spool, such that the follower shaft rotates some four times per single revolution of the take-up spool, requiring more threaded space on the take-up spool follower shaft. Curiously, the stop position for the feed spool follower is on the left side, while the stop position for the take-up spool follower is on the right side.

It is worth noting that the mechanical leverages for the two spool followers are very different. The feed spool and its follower shaft rotate at the same speed, and so it could be said that there is no mechanical advantage. However, the take-up spool follower spins four times faster than the take-up spool, which means that the take-up spool follower will tend to be moving about four times faster than the feed spool follower—give or take a little depending upon that amount of paper buildup on the feed and take-up spools. Because of the increased speed, the take-up spool follower will react more precisely, quickly, and provide a superior stopping force when it bumps up against the stop bumper spring. Having the take-up spool take precedence when it comes to stopping the rewind process is favorable, because it is important to brake and completely stop the take-up spool from spinning either simultaneously or a smidgen before similarly braking the feed spool. If the feed spool slows first the paper will loop, but if the take-up spool slows and stops first it will also stop any paper movement, which must, in turn, then stop the feed spool.

(Photograph courtesy of Dana Johnson.)

Revolver magazine with some not fully rewound music rolls in National piano #7524. Having music rolls rewind sluggishly or incompletely is a common problem for many timeworn, unkempt, grungy, and weathered National coin pianos. The torsion springs that supply the mechanical energy for the rewind process can become weak, bearings can gum up with old congealed oil, and the gearing and threaded follower shafts can be laden with dirt and grime. Moreover, the paper tension brake on the take-up spool hub must be adjusted so that it provides just enough paper tension during rewind, but not so much as to bog down the rewind system. And the spring pressure on the pinned music roll chuck (on the left side of the music roll spool) must not be so strong that it binds and impedes the rotation of the music roll feed spool.

In the words of restorers who have dealt with such problems, it takes very little unwanted frictional resistance within the rewind system to cause it to fail, especially when dirty and old and weakened torsion springs are used. It is imperative that all bearing surfaces, gears, and the threaded follower shafts be clean and sufficiently lubricated, and in many instances the torsion springs will need to be replaced with new, strong spring stock. The good news is this: when properly cleaned, regulated, and/or repaired the individual rewind systems should work reliably for a long time.

(Photograph courtesy of Dave Anderson.)

Left side of a music roll station in National piano #7125. Here the top part of the felted braking pad for the take-up spool hub is visible. The purpose of this braking pad is to provide a slight amount of tension to the music roll paper when it is being rewound off the take-up spool and onto the music roll feed spool. This tiny bit of tension keeps the paper from looping during rewind, and it helps to keep the paper wound snugly on the feed spool.

(Photograph courtesy of Dave Anderson.)

The left side spring loaded music roll chuck in National piano #7125. The music roll feed spool has a small cup in its non-keyed (non-powered) spool end. This cup is made to receive a rounded pin that projects outward from the left side roll chuck. The chuck housing consists of a hollow barrel with an exterior thread over which is screwed an adjustable split cap, The cap is split to grip the barrel snugly, and knurled so that it can be easily grasped when twisting the cap to adjust the pressure on an internal compression spring. The spring pushes against a plunger that is tipped with a rounded pin. which fits into the cupped end of the music roll spool.

The spring pressure on the rounded pin needs to be adjustable because of the frictional sensitivity of the torsion spring rewind system. Too much pressure on the pin and the rewind process will bog down and the music roll may not fully rewind; not enough pressure and the music roll may fall out of the revolver magazine. Thus, the chuck spring must exert just enough pressure on the rounded pin to keep the music roll reliably constrained, and yet not exert so much pressure that the rewind process fails to complete.

(Photograph courtesy of Dave Anderson.)

Right side of a music roll station in National piano #7125. This view shows the large diameter drive gear on the take-up spool, and above it the small diameter gear on the take-up spool follower shaft. The compression spring to the left of the small gear is the stop bumper spring for the take-up spool follower. The purpose of the leaf spring (between the take-up spool bearing and the follower shaft) is to keep the follower shaft pushed to the left, which, in turn, keeps the two spur gears engaged. When the release lever for the take-up spool follower (located on the left side of the roll station) is pushed inward the follower shaft moves slightly to the right just enough to disengage the gears. When the release lever is let go, the leaf spring forces the follower shaft to move back to the left, allowing the two gears to re-engage.

(Photograph courtesy of Dave Anderson.)

Roll station feed spool gears in National piano #7125. At photograph center are the music roll feed spool gears. The small gear is mounted on the keyed music roll chuck, which fits into a center hole with a slot off to the side that accepts a pin or key, so that the chuck can turn the feed spool during rewind without slipping. The larger gear (that meshes with the drive chuck's small gear) is attached to the torsion spring powered rewind shaft The large diameter gear also meshes with the small gear on the feed spool follower shaft, which is partially visible beneath the small chuck gear, but now easily recognized for what it is.

The metal clip under the hex nut that holds the chuck bearing in place, and that is then bent at a right angle over the small gear, has another right angle bend near its tip. This clip then keeps the shaft and attached gear for the chuck from falling out of the bearing when the music roll is pulled loose from the chuck.

Toward the bottom of the photograph is the top part of another, lower roll station, which shows the disengageable gearing for the take-up spool follower shaft. The compression spring on the shaft to the left of the small gear comprises the stop bumper for the follower. In this view the leeway between the small gear hub and the bearing plate is clearly obvious. When the release lever for the take-up spool follower (located on the left side of the roll station) is pushed inward the small gear moves to the right until stopped by the bearing plate, which is enough distance to disengage the gears.

(Photograph courtesy of Dave Anderson.)

Take-up spool floating drive gear framework in National piano #7125. The tracker bar (partially visible at front left) is in the up or Rewind/Roll Changing position, and so the interconnected little carrier frame that holds the take-up spool drive pinion is also lifted up and away from the revolver magazine. The motive power for the small drive pinion is the sprocket and flexible chain to the right of the little carrier frame. Within the carrier the geared end of the shaft is nudged downward by a spring, which allows the pinion to gently engage with the tracker bar framework is lowered, and the pinion can float up and down within limits, allowing it to adjust itself to slight imperfections when meshed with the large diameter drive gear attached to the take-up spool.