The pinwheel drum of the donor-machine was blocked - that is, no column would operate all pin-positions, pins were rusted solid in retracted position. Part as a rehearsal for overhauling the drum of the target-machine, partially to see if this drum could be better and partially just out of curiosity; taken apart for a cleaning and overhaul.
To take the drum out of a pinwheel calculator, one of the sidewalls has to be removed (i.e. a 'bracket', in Marchant-parlance). Then the drum itself can be taken out and apart. First step for that is to remove the pinned gear at the counter-side (the left in image below). Second is to remove the holding nut (red arrow).
The biggest challenge in cleaning this drum was the loosening of the holding-nut. This needed heat (soldering iron) and even some carefully-aimed hammerblows to start moving. (Clamp shaft in vise with protection, eg copper, don't apply any force to the disks!) The taper-pin of the counter-gear on the other hand came out easily. With the counter-gear and holding nut removed, all the sections of the drum simply slide off. Then a collection of 9 pinwheel disks, 3 carry-segments, clearing-arm, clreaing-arm-ring, a collar, one holding-nut, counter-gear, locking-comb, comb-pushpin, comb-spring and of course the main shaft:
The pinwheel disks are held together by two screws and a cover-plate. The carry-pins in disks 2 to 9 are peened in-place and cannot be removed. A brass disk, operating-ring, detent_spring, 9 pins, 2 screws and a retaining plate:
All disks (or dials) are different, specific to the angles of the specific dial digit-position. The timing of the pins and especially the tens-carry is staggered over the drum. The dimensions of the parts for every dial are thus different. Angles are given in the setting of the dividing-table of the slot milling machine.
The diameter of the drum is divided in 37 positions. Central 9 positions are needed for the setting pins, slightly staggered from disk-to-disk -to spread the load of turning the numeral wheels over the turn of the crank. Outside of this centre setting-pin 'field', there are the 10-carry pins spiraling out from dial 1. These carry-pins need one position offset from disk-to-disk to allow a wheel to do a full carry before the next engages.
The steel cams that reset the ten-carry levers are most clearly different; shown in this below drawing - these cams are all stamped with their position number.
The position-specific parts of a dial are all marked with their position number (an obvious and very useful thing to have in manufacturing) - below for example dial number 7:
Dial parts were cleaned individually: steelwool to de-rust the plate and metal-polish for the pins and ring. A very small amount of light, clean mineral oil (sewing machine oil) in assembly and some vaseline rubbed on the retaining plate against rust. When put together again, all pins move - although perhaps not quite as smoothly yet as they would have when new.
Taking apart the drum also revealed markings from the manufacturing process.
The drum of the donor-machine is marked at the outside of dial 1 with a date and initials. This suggests that employee RA assembled this drum on October 15, 1919 (a Wednesday).
Several -not all- of the pinwheels (or dials) are marked with initials TH scratched on the retaining plate. Individual disks were assembled separately, with employee TH scratching their initials into every disk they made on the obvious surface to do so.
Dials were first assembled and stacked per dial-number onto a stake on a wooden plate. There are even photographs of this in the Marchant factory around that time. A store of assembled
dials in a 'vault' cabinet from a 1918 article and stacks on a workbench in a cropped detail of
a 1920 photo captioned "service department" (?):
Another thing found out when comparing the two drums (and trying to exchange) was that the large driving-gear is not in a pre-determined position to the drum. That was surprising. It is a press-fit onto the drum-shaft that has the keyway to orient all the dials and parts. The gear teeth position appears to have been random, but at a first assembly of a machine the crank-handle shaft would be drilled for the handle. Thus the two shafts are matched in the angle of gears, they work on that specific combination. This was concluded from the gears on the drums of the donor and target machine not being at the same tooth-position.
The small angular-offset if mixing parts between machines is probably not too noticeable for a regular Pony, but for a Special with the check-dials it means that the check-dial gears won't mesh perfectly centred with the gear on ste setting-dials:
Effect of all this is that replacing a crank-shaft may mean also needing to exchange the drum-shaft. They are matched sets.
Anyhow, continuing the drum re-assembly in 2026. All the clean parts laid out and slid onto the shaft:
And put together again.
And then mounted into the target-machine - both drum and crankshaft from the donor-machine.
The target-machine original drum actually worked relatively fine after a little oil and a work-out. This donor-drum may in the end not be kept in the machine, it does however enable using the straight crankshaft. A restoration choice to be made later; straight shaft, but not the original for machine 70049 - an authenticity question...
The set of drum and shaft from 70049 now out of the machine, to get the same deep-cleaning and rebuild - no scratched-in date, but a stamped A-number instead. Maybe there are some hidden markings on the internals yet to be found :)
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