(Photograph courtesy of Dick Hack.)

Rewind/Play mode camshaft with cast iron bearing supports in National piano #348. In certain National coin pianos the main camshaft bearing supports are cast iron instead of the more commonly observed die-cast variety. The cast iron version of the worm gear clutch assembly casting, as pictured above, has been dubbed the pedestal style with a square base. It is functionally the same as pianos fitted with the more commonly observed die-cast components.

Described from left to right are the various camshaft related functions:

• Rewind/Play trigger pneumatic: This pneumatic triggers the Rewind/Roll Changing mode when the rewind pallet valve falls into the rewind cutout at the end of the music roll. A metal bracket attached to the top movable leaf of the pneumatic pushes down on the cam follower for the cam adjacent to the pneumatic (and on the left end of the camshaft).
• Rewind/Play cam: This cam has two lobes, each having a gradual fall that abruptly ends with a 90-degree angle rise. This 90-degree "cliff" face catches the vertical pin (on the cam follower lever) that rides on the outer rim of the cam, and then pulls the pin forward, disengaging the worm gear clutch.
• Worm gear clutch drive assembly casting: This iron casting supports the lower level worm gear shaft and the top level camshaft. The worm gear shaft extends out the back side of the casting, on which is (1) the clutch shifter sleeve, (2) the brass block holding the clutch pawl, and (3) a powered chain sprocket with a hub fitted with clutch engagement pins. The sprocket and hub spins freely on the worm gear shaft unless the clutch is engaged.
• Coin switch reset cam: It is a single lobe cam with a fast-rising short hump and then a quick fall at the end of the lobe. Its function is to reset the coin switch mechanism, turning off the power to the electric motor when the camshaft is completing its one-half revolution Rewind/Roll Changing mode cycle. The cam’s quick fall coincides with the stopping of the camshaft rotation.
• Spill valve vacuum dump (and play count) cam: Its sole purpose is to dump the vacuum supply during the camshaft’s one-half revolution Rewind/Roll Changing mode cycle, with the spill valve at its maximum open setting at the point when the camshaft rotation stops. During the Play cycle this cam has no effect on the spill valve. At the near end of the cam follower is a play counter, which tallies the number of music rolls played.
• Tracker bar lift cam: This cam follower for this elliptical cam consists of a steel u-shaped bracket attached to a heavy-duty lever arm. When the camshaft is positioned for the Rewind/Roll Changing mode the tracker bar is raised and the tapered locking hook that engages the revolver magazine’s slotted locking wheel is also raised, allowing the revolver to spin freely on its axis. When the camshaft is rotated into the Play mode position the tracker bar is lowered onto the music roll and the revolver magazine is locked into the correct rotational position.

Notice that what might at first glance appear to be a single shaft running along the front side of the camshaft mounting plate has attached levers that interact with two different cams. This "shaft" is actually two independent shafts, one inside the other. The smaller diameter shaft, extending more to the left, is used to trigger the camshaft into the Play mode position when a coin is dropped and the electric switch makes contact. The larger diameter hollow shaft is used to reset the coin switch, thereby opening the electrical circuit (if no other rolls have been selected) when the camshaft is rotated into the Rewind/Roll Changing position at the end of a music roll.

(Photograph courtesy of Bob Gilson.)

Cast iron worm gear housing for the Rewind/Play mode camshaft in National piano #348. Looking down on the worm gear clutch assembly, this view shows the overall detail of the worm gear casting and the associated clutch mechanism. The worm and worm shaft are not visible, hidden underneath the worm gear. To the right of the worm gear is a hard maple brake block, which applies just enough resistance on the shoulder of the worm gear to prevent the camshaft from creeping or wandering when the clutch is disengaged. Creeping is possible due to friction between the worm shaft and the sprocket with its attached clutch hub, because the worm shaft extends into and through the sprocket and hub, which then acts as a floating bearing.

Also floating on the worm shaft is the brass shifter sleeve for the clutch. It has a grooved ring on the lower end to accept a control yoke, and a cone shaped rise on the upper end that is used to forcibly disengage the clutch pawl. The pawl is nothing more than a spring actuated thin metal blade that is housed within a slot cut into one end of the rectangularly shaped brass block firmly clamped to the worm shaft. Above the brass block, the shiny steel clutch engagement pins that project outward from the sprocket hub are clearly visible. The chain sprocket and its attached hub are mostly hidden behind tracker bar tubing.

(Photograph courtesy of Bob Gilson.)

Clutch shifter sleeve and engagement pawl in National piano #348. This close-up view shows (1) the clutch shifter sleeve, (2) the rectangular-shaped brass block that holds the spring actuated clutch pawl, and (3) the clutch hub with three projecting steel engagement pins. Notice that the hub is drilled for six pins, but only three are installed. Most circular hubs have only three pins installed. a few six pins, whereas all triangular hubs are limited to just three engagement pins.

Between the clutch hub and the brass block, one end of a brass bearing sleeve can be seen. This bearing sleeve goes into and through the hub and sprocket and rides freely on the back end of the worm shaft, which acts as a floating bearing for one end of the sprocket shaft. The brass block is clamped onto the worm shaft, and has a deep slot cut into the working end, which is also drilled for a small compression spring that works to keep the clutch pawl in the engaged position. The pawl itself is nothing but a stamped piece of steel roughly in the shape of a common pistol. There is a pivot hole next to what might be compared to the pistol's hand-grip, with the "barrel" of the gun being the blade that swivels inward or out to engage one of the pins on the clutch hub. When the clutch shifter sleeve is fully pulled forward until it contacts the worm gear casting the cone shaped rise at its far end forces the clutch pawl blade to swivel inward, toward the center shaft, it therefore missing any of the hub clutch engagement pins. When the shifter sleeve is allowed to snap to the rear, the spring in the brass block pushes the pawl blade outward and into the path of a hub clutch engagement pin. It is exceptionally simple but effective clutch, but useful for only relatively slow speed applications.

(Photograph courtesy of Dick Hack.)

Rewind/Play mode camshaft with die-cast bearing components in National piano #7352. National pianos with the more modern looking die-cast components are functionally equivalent to those that embody the rarely seen cast iron bearing components. Die castings have a satin smooth surface and are designed to slip out of a machined mold, whereas cast iron uses a packed sand molding process, which makes the visual differences between the two casting methodologies immediately obvious. For details on the individual cams and their functionality please refer to the top image description. The clutch hub differs from the top image in that it has a triangular hub, instead of a circular hub.

(Photograph courtesy of Dave Anderson.)

Die-cast worm gear and clutch assembly without the Rewind/Play trigger pneumatic in National piano #7474. In this angled view both the worm and the worm gear are visible. The clutch hub is triangular with three clutch engagement pins. With the Rewind/Play trigger pneumatic removed the clutch operating lever and the cam follower attached to it can be easily seen. Behind the 2-lobe cam on the left end of the camshaft is the cast bronze clutch operating lever. Its pivot point is at the left end, in the middle is the cam follower lever, and at its right end is the end piece that moves the clutch shifter sleeve longitudinally forward or rearward.

The pivot point consists of a small die-casting with a top bearing surface that is flat, and with a protruding pin about which the left end of the clutch operating lever can swivel. The pivoting end of the lever does not have a simple hole, but rather a slot going from front to rear (mostly obscured by a length of rubber tubing). An adjustable tension spring is attached on the rear side of the slot area, which pulls the left side of the lever to the rear, forcing the bearing pin to be nested against the front end of the slot. Thus, the swivel point is normally the front end of the slot. So why a slot? When the Rewind/Play cam pulls the cam follower (attached to the center point of the clutch operating lever) forward it does so with great mechanical leverage, i.e., a lot of potential force. The clutch pawl cannot disengage until the cone shaped end of the shifter sleeve has moved almost fully forward, only then forcing the pawl to disengage, but then soon stopped dead when it comes up against the rear worm shaft bearing. There is not much leeway between the moment the clutch pawl disengages and when the shifter sleeve contacts the rear bearing. Once the shifter sleeve contacts the rear worm bearing any additional pulling motion by the cam follower will be taken up by the slot at the pivot end of the clutch operating lever. And so, the purpose of the slot is to provide an outlet for any travel overshoot due to spin-down time or mis-adjustment when the cam follower is pulling back on the clutch operating lever.

The cam follower lever is attached to the mid-point of the clutch operating lever by means of a mounting that allows it to swivel freely up or down. Using a simple spring in front of the worm gear clutch assembly casting, the cam follower is pushed upward so that a pin on the follower lever always rides against the outer rim of the Rewind/Play cam. When the Rewind/Play cam rotates the steep face at the end of each lobe will catch the follower pin and pull the clutch operating lever forward, disengaging the clutch and then stopping. At this point anything that pushes down on the cam follower lever will push the follower pin off of the lobe face, allowing the clutch operating lever to snap to the rear and engage the clutch, stopping again after 180 degrees of camshaft rotation.

(Photograph courtesy of Dave Anderson.)

Angled view of the Rewind/Play mode camshaft with die-cast components in National piano #7125. This view is included to better show the contouring of the cam-work located to the right of the worm gear clutch assembly casting.

(Photograph courtesy of Dick Hack.)

Tracker bar lift cam and cam follower bracket with attached levers in National piano #7352. This image shows the end cam and its u-shaped cam follower that raises and lowers the tracker bar framework. Looking down alongside the left side flange on revolver magazine is the notched locking wheel and above it is the cast bronze locking lever, which has a hook that slips into a notch on the locking wheel when the tracker bar is lowered.