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The photographer's stamp on this photo reads: HALL & CO. Commercial Photographers 20 Hunter Street Sydney
Having mentioned the upper large shaft that runs the length of the unit with the large cog attached to the left hand side, this is a very interesting piece of mechanical technology. It is a delay line! I am well aware of delay lines in electronics but this seems to be a mechanical counterpart long before the electronic systems that made this concept commonplace. An early digital computer era memory was based on a mercury delay line. Unlike the early computer memory this mechanical delay line has no need for refreshing as it is read and processed, prior to the end of the delay line is reached. This device was called a Storage Screw however it can be thought of as a type of memory. Storage, there is another major digital computer concept! There is a second storage screw in this adder near the bottom with almost the same dimensions and orientation. The adding shaft that drives the second Storage Screw is a lot smaller than the upper adding shaft yet is clearer to see as the assembly is vertical rather than slanted away from the viewer. The need for the storage screws originated from a problem associated with inertia. The adding shafts with their escapement wheels and epicyclic gears could respond quickly to the demands of betting as they were relatively low in mass. These adding shafts are on the right hand side of this image and drive the storage screw from the right hand side. When it came to large counter wheel indicator displays like the one on the front of this adder, these had to overcome significant inertia. In simplistic terms, as transactions are recorded as increments of rotation generated by the adding shafts, a screw is wound into a nut by the fast response part of the machinery capable of keeping up with the requirements of the bet traffic. At the other end, in this case the end with the large cogs, the nut is unwound from the screw at an angular velocity change rate that the slower equipment can accelerate or decelerate at. In the case of acceleration, the slow to accelerate equipment will eventually reach an angular velocity in excess of the storage screw and start to return the screw to its rest position. The screw remembers the rotation generated by the high acceleration adding equipment and is read at the other end at the slower lagging velocity of heavier equipment until acceleration ends and the heavier equipment reaches an angular velocity greater than the screw. For the analogy of the screw and nut to be effective we have to dispel the common visualisation of a nut and screw. The nut is the shaft itself which is threaded on the inside. The screw is like a grub screw and travels up and down the inside of this shaft. The outside of the shaft only starts rotating when the screw inside it leaves its rest position as a result of the screw travelling along the nut as a result of bet traffic. To have a look at an Engineering Drawing of this storage screw, go to the Figures from George Julius' paper presented to the Institution of Engineers Australia in 1920 section of the second page of the Photo Gallery by clicking on the image, scrolling down to the bottom of the first page of the Photo Gallery clicking on the next page button of the navigation bar then scroll down to the section mentioned. There are also images of engineering drawings of the adding shafts and escapement assemblies in this section.
I have chosen this image to write about the mechanism that locks the driving gear as this image has the most prominent view of this part of the machinery. Following is a short extract from a Paper George Julius presented to the Institution of Engineers Australia in 1920. This extract relates to the storage screw. The epicyclic gears are made as light as possible, and are urged forward by " coil springs " and not by "weights." This ensured the instantaneous response of the epicyclic gears to the demands of the ticket-sellers. The movement of these gears so obtained is transferred to a " storage " screw which serves two functions, firstly, that when the machine is at rest it locks the driving gear which operates the counter wheels, and, secondly that when issues are to be recorded, it stores-up the records until they are registered by the counters. Immediately the tickets are issued the epicyclic gears instantly operate, being driven by the coil spring, and in so doing they turn the screw which then unlocks the driving gear for the counter, and the counter begins to operate. In so operating, this driving gear also moves a nut, which, acting on the storage screw, tends to bring it back to its normal position of rest, and thus again lock the counter driving mechanism. Thus the epicyclic gears in picking up impulses received from the ticket-sellers move the screw backwards, and the, driving gear of the counter is always trying to overtake this movement and thus return the screw to its normal position. This locking mechanism George mentions, can easily be seen in this image. Looking on the left hand side of the adder at the top large cog, which has the upper storage screw at its centre, come left past the left hand side mounting frame of the adder and you see a rod projecting left from the storage screw. This is part of the storage screw position sensing mechanism. At the point where the rod disappears into the storage screw, there is a bracket attached to the left hand mounting frame of the adder, which extends upwards and left at 45 degrees to the storage screw. At the end of this bracket is a hinge. Attached to this is a moving arm consisting of two metal strips which project downwards to the drive pulley for the gear that drives the large cog, that we started with. At the bottom end of this arm, is a projection that engages with a stop on the shaft that drives the cog that turns the upper large cog that rotates the storage screw nut. This projection on the arm and stop are hidden behind the drive pulley. This is the locking mechanism that George is describing. Once the storage screw starts to move as a result of transactions from the adding shafts being recorded, the first thing that happens is that this arm moves to disengage the lock and allow the drive pulley to rotate the large cog which turns the nut part of the storage screw. There are some video clips in the Video clips of a working Julius tote chapter of this website that show this release mechanism associated with the storage screw working. The adders in the video clips are more modern than the one in this image and are larger, being mounted on tables. The audio track on these video clips clearly conveys the clanking sound of these locks being disengaged. The clips that show these locks in operation are titled The forecast pool adders and Place GT and forecast adder internals. These can be viewed here.
Inside the drive pulley in this description, there is a clutch which slips when the locking mechanism is deployed. To the left of the pulley before reaching the end of the shaft on which it rotates a spring is visible. When the pulley is rotating this spring is wound. The energy to rotate the adding shafts comes from this spring. This is an important concept as the drive to the pulley being discussed is continuous and betting is start stop and erratic. There has to be a means of disengaging from the constant drive when no betting is taking place.
A second extract from George's paper mentioned above reads The movement of this screw is so arranged that it also controls a variable speed friction gear through which the counters are driven. During any period of acceleration in the issue of tickets, the screw is withdrawn in the nut faster than the counter operates, and this through the friction gear speeds up the counter, and the nut, in an endeavour to overtake the movement of the screw, and a condition of balance is ultimately established. If the issue of tickets is retarded or ceases, the nut immediately gains on the screw and brings it forward, thereby picking up all the stored-up records, and by means of the friction gear gradually slowing down the counter until when all the records are recorded, it quietly comes to rest. The rotation of the nut also is utilised to continually rewind the coil spring which operates the epicyclic gears, and thus ensure a steady driving effort on these gears. At the end of the rod that projects out of left hand side of the upper storage screw, which is part of the storage screw position sensing mechanism, there is a hinged arm projecting down from a mounting above, which has a hinged tip at the bottom end making contact with the left hand end of the storage screw position sensing rod. I think this is part of the variable speed friction gear that George has described. I have never seen one of these adders, however from this photograph and the following photograph in the Photo Gallery it is possible to deduce an overview of how it worked. To find out more, go to the next photograph in the Photo Gallery which shows this adder from a different angle. Click on the image then click on the next image thumbnail.