LETCHWORTH ENIGMAS – Electrical
The wiring on the back of the commutators runs from the binder posts at the top and bottom. Because the ‘go’ and ‘return’ paths are separated there are 52 wires from binder posts to commutator and from commutator to commutator. This adds up to 208 wires, each with a small tag soldered to each end. 416 tags in total. This all has to be multiplied by 36 to give the grand total. Between each commutator can be seen a wire guide. Wires have to be threaded through these before the second tag is soldered in place. Hence there are four sub assemblies to make up. These are then mounted on the jig as shown. When completed the whole set of commutators and binder posts are removed from the jig and transferred to the machine.
In order to obtain the correct drum brush pressure the commutators have to be shimmed out until an end reading dial gauge on a specially made ‘in house’ jig indicates the correct reading. The dial gauge is rotated over the face of the commutator to ensure that there is no ‘swash plate’ error. If there was this had to be corrected before continuing.
When the sub assembly is in place the binder posts are screwed to their mountings. Then, when a whole bank of twelve Letchworth Enigmas are in place the single pins on the end of the cableforms can be plugged into the binder posts. These cableforms were previously fitted
In this view the small tags can be seen. They are fitted under flat brass washers and held down by small 3-48 screws. Just fitting the washers and screws is not an insignificant task with around 16,000 of each required. Mary Hillyard fitted all these.