Michael,
An excellent summary of multi-function machines in general.
Regarding your (3), I think the reason this concept keeps getting reinvented can be best identified as Greed.
The punters are greedy to get as much functionality as they can, in terms of (i) financial expenditure, and (ii) allocation of space. … They want it to be possible.
The manufacturers are greedy to Sell a lot, whilst Providing only a little … If I can persuade you that my multi-machine is three machines in one; then I can easily charge you for [say] two of them. <etc.>
MichaelG
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For those who may not have looked …
Mr Urwick's Patent, although it uses the metalmaster as an example of implementation, really concerns the triangular gib key. This, as Michael indicates, is nothing very special in terms of its apparent function … but the important thing [and the patentable invention] is the novel approach to obtaining alignment on a cylindrical shaft.
It is generally much easier and cheaper to make matching 'shafts and holes' circular in section; but then there is no positive alignment in rotation. Users of the small mill/drill machines will be familiar with the problem. … hence my earlier comment in response to KWIL.
The patent offers a low-cost manufacturing solution … the end result cannot be "better" than the equivalent square or triangular alignment mechanisms BUT; for a given level of accuracy it will be much cheaper to manufacture.