(Photograph courtesy of Dick Hack.)

Cast iron bearing posts for the music roll selection control sub-System in National piano #348. The two separate front bearing posts support (1) the wooden belt pulley used to rotate the revolver magazine, and (2) the tooth clutch shifter sleeve. The chain sprocket at the far right provides the motive power for the clutch shaft, while the sprocket to its left, in turn, supplies the motive power to a randomizer device that operates in conjunction with a retrofitted dog race diorama.

The 3rd bearing post, centered behind the clutch shaft, supports the lever arms that control the tooth clutch. The brass colored lever arm on the front side of the bearing post has a yoke that moves the tooth clutch shifter sleeve one way or the other. The steel lever on the backside is connected to the tracker bar framework: When the tracker bar is raised the tooth clutch is engaged (Rewind/Roll Changing mode), and when the tracker bar is lowered the tooth clutch is disengaged (Play mode).

The 4th bearing post, to the right and behind the clutch control levers, supports the shaft that synchronizes the rotational position of the revolver magazine with the studded cylinder in the coin switch mechanism. It is this studded cylinder that triggers the system into the Play mode when the selected music roll is correctly positioned underneath the tracker bar.

Note that on the vertically oriented wire linkage, which connects the tooth clutch control lever arm to the metal tab connected to the tracker bar framework, there are leather nuts on both the top and bottom side of the metal tab. National originally only used a rounded leather nut on the bottom side; never the top side. Doing it this way allowed the serviceman to easily push down on the tooth clutch lever and then freely spin the revolver magazine, making it easy to position it when working on and/or changing music rolls.

(Photograph courtesy of Dick Hack.)

Integrated die-cast bearing support for the music roll selection control sub-system in National piano #7352. This integral layout is functionally identical to the design requiring four separate bearing posts. With this design all components are kept perfectly aligned with all four bearing posts being an inseparable part of one convenient mounting base. Notice that the belt pulley is also die-cast, instead of a wood pulley. This piano was also retrofitted with a dog race diorama, with the chain drive sprocket for the randomizer device affixed to the left end of the clutch shaft.

(Photograph courtesy of Dick Hack.)

Closeup of the tooth clutch in National piano #7352. Here the jagged two-part tooth clutch is shown engaged (with the tracker bar frame raised). The tooth clutch consists of two mating toothed brass sleeves. One sleeve is pressed into the die-cast pulley, forming a clutch hub and the bearing on which the pulley can freely spin. The other sleeve, the clutch shifter sleeve, is keyed to the clutch shaft and therefore must rotate with it, but it can slide to and fro on the shaft as controlled by the brass yoke that engages a groove in the non-toothed end of the shifter. The pointed tooth design insures that the clutch will always engage smoothly, and not hang on a blunt tooth edge when the tracker bar frame is suddenly lowered.

(Photograph courtesy of John Perschbacher.)

Closeup of control linkage for the tooth clutch lever arm in National piano #794. This photograph shows how National originally configured the wire linkage that connects the tooth clutch control lever to the metal tab fastened to the tracker bar framework. This is perhaps a trivial seeming detail, often overlooked, but important nonetheless. The hole through the end of the long metal tab reaching out from the tracker bar framework is chamfered. The threaded end of the connecting wire dangling downward from the tooth clutch lever arm goes through the hole in the metal tab. Then a rounded leather nut is threaded onto the wire and adjusted so that when the tracker bar framework is fully raised the tooth clutch is disengaged. The rounded leather nut is meant to fit comfortably into the chamfered area around the hole, so that the wire can freely wobble from side to side as the attachment end of the clutch lever arm traces an arc when it is raised or lowered. Underneath the leather nut are two brass nuts used to lock themselves and the leather nut in place and prevent any eventual slippage. Notice that there is no nut above the metal tab, which is unnecessary because there is a coil spring that works to keep the lever arm constantly raised, and the rounded leather nut snug against the metal tab. The reason there is no nut on the topside is this: When a serviceman was in the process of working on and/or changing music rolls he could reach up and push down on the tooth clutch lever and then freely spin the revolver magazine to whatever position was necessary. With a nut on the topside of the metal tab the tooth clutch cannot be easily disengaged, making the changing of music rolls a much more challenging task.

As a side note, when the National field agent arrived on his weekly mission to change music rolls he carried a case that contained a selection of unspooled but tightly wound music rolls, and a handy device to easily unspool and then re-spool new music onto the removable feed spools. National music rolls had tapered leaders on both the leading and trailing ends, with the music rolls transported without spools and in a wound up state with their tail end exposed.

(Photograph courtesy of Dick Hack.)

Overall plan view of the music roll selection control sub-system in National piano #7352. At far left is the integrated die-casting for the tooth clutch with its four bearing posts. At far right is the coin switch mechanism. About mid-way between the front and rear of the coin switch enclosure is the studded cylinder that works to trip the player system into the Play mode when the selected music roll is located underneath the tracker bar. The shaft connected to the studded cylinder extends left to a chain sprocket, which is, in turn, connected by a chain to another identically sized sprocket affixed to the center axis of the revolver magazine. The tooth clutch mechanism working in conjunction with the coin switch mechanism makes up the basis of the music roll selection control sub-system.

(Photograph courtesy of Dave Anderson.)

The tracker bar framework and tooth clutch mechanism in National piano #7125. This view is included to demonstrate the relationship between the tracker bar, revolver magazine, and the tooth clutch mechanism. At far left is the cam that raises and lowers the tracker bar frame, in the middle is the revolver magazine, and to the right is the tooth clutch mechanism. In this photograph the tracker bar is in the process of being raised and the tooth clutch has just started to engage. The music roll is in the process of rewinding, which began the moment the tracker bar frame lifted, disengaging the spur gear that drives the take-up spool.