Cypher machines maintenance and restoration spanning sixty years

Cryptologia, Jul 2003 by Clarkson, Dorothy

For the Mark III I had the assistance of another Volunteer whose main interest was teleprinters but who, in the fifties, had had a course on the machine, had never worked on one but had a set of notes which proved invaluable, especially when it came to setting up. Earlier I referred to this machine as "portable" -I think a more accurate description would be "transportable" as it is quite large and heavy. For those who are not familiar with this machine the following may be helpful: it uses the same drums as the Mark II series but is hand-cranked although there is provision for the attachment of a motor drive. The speed is governed to a maximum 60 operations per minute against the 300 of the Mark II series. Printing is by means of a wheel with the characters embossed on the periphery, continuously inked by a roller and against which the single strip of paper is pressed, hence there is no reference tape. The mechanism revolves once for each key press, the wheel being raised for upper case characters. Electrical power is produced by an impulse generator at the beginning of each revolution, stored in a capacitor and released when the appropriate character reaches the printing head to energise a small relay which trips the printing head to press the paper momentarily against the wheel. Because of this method of printing and the small amount of power available, all adjustments are very critical.

Superficially the machine appeared to be in a similar condition to the 22, having been kept in the same cabinet, both having appeared in the TV programme but far more dismantling was required to enable the removal of dried-up lubrication. There were several wiring faults where tight lacing had precipitated fractures and careless assembly had crushed two wires, causing short-circuits. The counter required a new internal non-return spring, which I was able to manufacture but again the main problem was the drum drive, in this case all five pawls being immovable. Fortunately there were no parts missing and although the capacitor was below its nominal value it was still good enough to operate the relay satisfactorily. Partly because of my unfamiliarity with its mechanism but mainly because of the critical nature of the adjustments, this machine consumed some 140-150 man hours, spread over twelve weeks but was eventually fully operational.

Finally to the Mark 23 and that was a different story altogether: I was told that it had been used for instructional purposes and frequently dismantled and had obviously been left uncovered for long periods. It was very dirty, clogged with dried oil and grease and with a number of parts missing, in addition to those that I had removed. The drum feed mechanism had the same seizures as the Mark III and several of the printer solenoids had broken cheeks and connections. On one printer the casting carrying the paper and ribbon feed mechanism was distorted, with two corners broken off, leaving two bearings floating in mid-air. It-is virtually impossible to straighten castings of this type (so-called 'white metal') as they are very brittle and I didn't even try, in fact I was surprised that this one was still basically in one piece after the knock that it must have received. The general appearance indicated that the assembly had been dropped while in the 'open' position. I managed to build up the casting, positioning the bearings so that the shafts were in the correct alignment and manufactured replacements for all the missing parts, with the exception of the paper reels and guards which were beyond my capacity as I did not have the necessary materials. A large number of screws were missing, of various sizes and lengths and all to the old B. A. (British Association) standard. I was told by every merchant that I visited that these were available to order but only in commercial quantities and none had any in stock. (In some places younger members of staff didn't even know what I was talking about!) Fortunately I had some of the larger sizes in my scrap box, left over from various projects carried out many years ago and finally found the smaller sizes in a local model shop. Eventually, after around 130 hours of work, much of it in my own workshop, the machine was serviceable but not usable because of the lack of the tape reels.