Stack Installation and Final Steps

Now that your stack is completely assembled and thoroughly tested, let’s put get it back in the piano (do read the previous post for prior steps, if you have not already).

Carefully put the stack back in its home, without touching the hangers against the piano wippens. Slide the stack back into place and secure it with the large screws.
Install the tubes for suction supply to the motor, and the damper pedal feed, as well as any other expression devices or the shifter if necessary. Ensure that this tubing does not kink or interfere with the piano action.

Connect the mechanical linkages for the tempo indicator rod and the transmission; these need to be regulated mechanically, so that the range of motion of the control levers is optimized.

Tempo and Rewind/Play levers

For the play/reroll lever, regulate the linkage so that when the lever is in play position, the pinion engages with the take up spool gear; it should engage positively, but not so much that it bears strongly onto the gear. When the lever is moved to the reroll position, the pinion hub should slide over enough so that a protruding pin (or other arrangement) engages the reroll sprocket so that now the motor is powering the reroll clutch shaft above.
In conjunction with the transmission, the play/reroll lever must also cleanly activate the stack cutout valve, so that when in reroll mode no suction is supplied to the stack, in order that you don’t hear the music playing backwards at high speed!
Conventionally, a player action features a governor override valve, so that when in reroll mode, the air motor receives unregulated (maximum) suction to reroll as quickly as possible.
When in play mode, this valve should be firmly closed to ensure accurate functionality of the governor, so check that this adjustment is regulated properly.

The tempo lever regulation is coordinated with the tempo valve and the indicator / pointer found at the bottom of the spoolbox (normally). When the tempo control lever is all the way to the left, the tempo is theoretically “zero”; the v-slotted tempo valve in the lower action or governor should be closed, which means that the air motor is receiving no suction and does not turn. Adjust the pointer rod so that it accordingly reads zero at the indicator. Likewise, when the lever is all the way to the right, the tempo valve should be wide open now, but just so. This should correspond to a tempo reading of 120 on the indicator. A further check is that the motor should just begin to turn when the pointer indicates a tempo of approximately 10.

The tempo indicator, sitting at the bottom of the spool box. The small tempo pointer is highlighted in black. Note that there is also a larger pointer which can be adjusted to a relative position on the music roll, to follow tempo change suggestions on certain music rolls which are annotated in that way. Normally these indications appear as coloured lines which weave left and right across the roll.

With this done, now the governor itself needs regulating. The above regulation needs to be done well, for the following regulation to be effective. The spring tension of the pneumatic and knife valve need to be calibrated as follows: At a tempo of 70, seven feet of paper need to pass the line of holes in the tracker bar. You will probably need to manually measure and mark this on your test roll, as I did.

Timing lines marked on a test roll, at 1 foot intervals

With the test roll accurately annotated, play the roll from the starting point, marking time on a stopwatch. If the 7′ mark arrives before time, it is running fast which means you need to weaken the retaining spring of the governor pneumatic. Conversely if the roll is running too slow, you need to tighten the spring. Although it may seem tedious after all the other regulation which has already been done, it is important to get this final adjustment just so, to ensure smooth and reliable playing.

A motor governor with typical design features. The spring marked “2” can be turned in the retaining bracket “3” so that the tension level is increased or decreased.

Leave a Reply

Your email address will not be published. Required fields are marked *