Dave Calway worked in the machine shop and remembers having to be extremely precise with his measurements

In the machine shop, your lathe work or your milling would be within say perhaps, plus or minus a thou’ – one-thousandth of an inch and your general limits would be plus or minus ten thou’ and that was a very generous limit. But if you went on to grinding then, you know, you were down to tenths of a thou’ and your dimension or diameters would have to be accurate within the tenths of a thou’ and, of course, the finish had to be there as well. You had to have them gleaming. That’s precision work and obviously, you’d get more highly precision work, but that is precision work as compared to commercial work, which had got greater limits on them.

What equipment were you using for that?

Well, we used to use, in the main, there were micrometres which measured in thous. You had Verniers which were like, how can I say, a clamp which would measure to within a couple of thou’ and you also had dial indicators, you know calipers, which once you put them on a diameter, you would put a few little slits in there and they would measure within thou’s and within microns, well not microns but tenths of a thou, you know. The equipment was provided and it was regularly checked to make sure that they held the limits. Then, of course, we had plug gauges which were ground and brought in, that one end would fit and if the other end would fit it was too big and no good at all.

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