Switch manufacture
Manufacturing details of switches are not widely known. Some details are disclosed in patents, but many others remain a mystery.
Contents
Assembly
Switch production was initially manual to some extent. Meryl Miller provided a photograph of a factory worker assembling a Datanetics DC-50 switch using a special jig, although the switch elements (the metal–mylar sandwich) were automatically fabricated on a continuous production line.
In 1974, Oak Industries placed an advertisement in Electronics in which they mentioned what they considered to be “the most sophisticated fully-automated keyboard switch assembly facility in the industry”. The advertisment covered Series 400, 415 and 475 and did not state whether this automated production line covered all their series, or just one or two of them.
Cherry M8 was reported by Peter Cherry to have been the “first keyboard switch to be assembled automatically, a feat that everyone said could not be done.” The exact date of introduction of M8 remains a mystery but it appears to have been somewhere between 1979 and 1981. How this claim compares with that of Oak’s claim for fully-automated assembly in 1974 is not known, owing to lack of specific details of either production line. MX assembly in Germany was fully automated.
Some Tai-Hao APC Series switches have a reversible base, that can be attached in both the 0° and 180° orientations. The reason for this design, they reported, was to permit automated assembly of the switches. As APC Series was introduced around the start of the 1990s, it would seem that automated assembly reached Taiwan fairly late, as the reversible base appears to have been a later modification and one that would later be removed.
Moulding
Günter Murmann, formerly Cherry’s VP of engineering in Germany, cited a limit of 5 million shots per mould for keyswitches before the moulds needed replacing, with a nine-month turnaround time for mould replacement. For Cherry MX, the moulds contained over 60 cavities, for a total of 300 million switches per mould produced within the mould’s lifetime. The actual lifetime of an injection mould depends on the quality of the materials used: there is a trade-off between cost and longevity.