Thanks to Bob's link previously to Precision Parts
, that has given me the nudge required to design an adapter between a FD 50mm f/1.2 lens and a donor EOS lens mount I recycled from a dead Sigma. This was supposed to be my cheap way to get f/1.2 on a DSLR compatible lens, but I failed in my previous attempts to bodge the mount and lens together.
It took 4 designs and the whole evening, but I got finally something is can be made for a sane cost. The biggest problem was that the screws required to join the adapter to the lens are covered by the opposite end required to connect to the donor mount. So I set about creating a two part design, one part each joining to the two ends, and can also be joined together easily.
Design 1: internal thread screwed together. Non starter. There just wasn't the space for it.
Design 2: outside thread screwed together. This made it much wider, but this could work. The biggest drawback was the complexity of both parts, thus I abandoned this as too expensive at $300 estimate for the two parts.
Design 3: No threads, screw the two parts together using screws through them as opposed to threads on the parts themselves. While it eliminated the costs of the screw threads and simplified the parts, the through holes weren't much cheaper, and even worse if you wanted them tapped. Plus there isn't much space to put screws sideways anywhere as the whole thing is a nominal 3.3mm thick.
Design 4: Single block. Cheapest yet! But higher risk as it means I have to do the drill holes myself. Blind holes for the lens side join is quite high risk. Mount side can just tap in easily enough I think.
I am now officially sick of measuring things. And as I had a drink before starting, I'm not trusting my figures so I'll double check these tomorrow. As they say, measure twice, cut once.