The distinctive case of the Models H and J Comptometers is built up from a number of separate panels:

• A heavy base of bright plated steel. The mechanism is fastened to the base plate from underneath.
• Four decorated side panels, screwed to the base from inside the case and reinforced with screws in the corner pillars.
• The top or "key plate" of 0.040" steel, attached to the mechanism by screws and internal clips. The plate acts as the upper guide for the keys.
• The numeral wheel escutcheon and decimal indicators, attached to the mechanism by locating pins and two screws.

The base, sides, and top are lined with sheets of linoleum about 3/16" thick to absorb both sound and oil. (Linoleum is a rubberised cork compound with a hessian backing, widely used as a floor covering in the days before sheet vinyl).

The steel panels are copper plated and lacquered to give a rich "metallic" finish. The Comptometer logo and scrollwork are embossed into the side panels and polished to a contrasting finish. The case alone weighs over 7 pounds, before any of the mechanism is added.

The case can be removed from the mechanism by removing the numeral wheel escutcheon, the clearing handle, and the four countersunk screws near the corners of the base, and then separating the sides from the top.

The mechanism is a close fit inside the case, and will probably be stuck to the linoleum in many places - especially if it has not been moved in fifty years. It is best to separate the case with the machine standing on its back, then place it gently on the keys and lift the case straight off. Be careful not to damage the keys.

It is not necessary (or helpful) to remove the screws in the keyplate or the corner pillars, and one should never attempt to remove the keytops.

Even when removed from its case, the Comptometer retains its rather monolithic appearance and reveals very little of its inner workings.

(Readers may note that this and the previous illustration show a different 10-column machine. The idea is the same).

At this stage we will engage the services of the workshop fairies to disassemble and clean the mechanism (over a thousand parts and sub-assemblies, comprising well over 2000 manufactured parts), so that we can re-build the machine "from the ground up" and study its construction and operation.

(A sequence for disassembly and reassembly is given in the final chapter. It will make much more sense after we know how it all works).

The frame of the Comptometer is built up from a series of complex and rather elegant side plates measuring 14" x 4" (approx) and pressed from 0.037" steel. The plates are supported by ten cross-shafts or tie rods (5 x 0.227" dia, 5 x 0.155" dia), and are held at just under 3/4" separation (0.742" centres) by 13 rolled and pressed sheet-metal spacers on each of the shafts.

The mechanism is built up between the side plates as a series of more-or-less identical columns. The components of the mechanism are supported on a total of 25 shafts or rods that pass crosswise through all of the plates. The mechanism shafts vary from 0.055" to 0.108" diameter.

Although the frame plates are basically similar, they vary in the detail of their attachments (rock frame toggles, keyplate bushings, Sterling gearsets, etc). There are 14 plates in this 12-column machine, and 11 of them are different.

Likewise, the spacers are mostly 0.705" wide, but there are many variations. Great care needs to be taken if the frame is to be disassembled.

The frame is mounted between a pair of heavy truss-like support plates pressed from 0.084" steel. The tie rods enter the corresponding holes in the support plates to provide a positive location. Tightening the screws in each tie rod pulls the side plates and spacers tightly together to provide a very stiff and rigid assembly.

Shims are fitted where necessary to maintain clearances as the tie rods are pulled up tight. Four of the five larger tie rods have a trick nut behind the right-hand support plate, so that the support plate can be loosened or removed without disturbing the rest of the frame.

The "zero-signal" bell is visible near the back of the left-hand support plate. The clearing handle attaches to the boss near the centre of the right-hand plate. The "feet" under each plate secure the whole assembly into the case. The serial number is stamped into the "tail" at the top rear of the left-hand support plate, as well as into the keyplate near the leftmost "1" key.

The "Rock Frame" is a major sub-assembly which mounts in the gap at the lower front of the main frame. It is constructed in the same fashion, with three supporting rods and spacers. The rock frame has its owm serial number, stamped into the right-hand end plate.

The rock frame houses part of the gear train and the carry mechanism (described later), and "rocks" forward during clearing to disengage the gears and allow the numerals to return to zero.

The case and frame to this stage contain over 600 manufactured parts.