Just one photo perhaps? I would love to see one somewhat close to what we are looking for. It would help narrow down the goose chasing.KenChan Wow! That is fantastic work! I am leaning toward your assertion that perhaps these are not perfect circles but abnormal holes. The larger photos are very helpful along with your detailed renders of your designed disc.
Possible side observation:
In some of those photos, the V8 Rod is missing, having been knocked off. Is it just me or does it appear that, based on the location of the larger hole on the disc, in relation to other features of the Webley, the disc itself is moving/rotating slightly? Perhaps that might be telling somewhat as to how the builders attached these discs?
I think there is some logic to your line of reasoning, however, the deeper I have dived into vintage high speed audio equipment that utilize pulleys (from the era that these discs/pulleys would likely have come from), I am regularly surprised by what would appear to be randomly positioned holes on pulleys (I am sure the reality is they are not randomly placed) for what I have to believe are reasons of balancing these pulley wheels at high rotational speeds. Even more strange is the varying quantity of holes per pulley, as well as their differences in hole size and in the arrangement of each hole to one another which typically, to the naked eye, is not what one would consider symmetrical (which one would assume to be necessary for balance).
I don’t want to infer every one of those pulley wheels was custom balanced, nor do I want to make it seen that most or even half of them are this way (the vast majority are not like this), but a surprising number of them are very irregular.
Of course now that I’ve said this I can’t seem to find any good reference pics.