Having spent many years assembling and using electronic wiring, if the connector has only 4 pins it is because it needs only 4 pins: there are only 4 wires in the cable. Nothing wrong with “aircraft”-type rather than D-connectors, especially if genuinely to military or high-grade commercial quality. You’d need change them only to suit the replacement units. Why replace those anyway?
My milling-machine is a second-hand one too old to have been designed for DROs and the like, but I installed a 3-axis set by M-DRO, not something unknown from some Internet supermarket; and I am very happy with it.
The company knows our needs, and can supply what is right for the machine as well as user. I think I placed my order at the company’s stand at one of our exhibitions – certainly discussed it with the stand staff.
[Besides “our” suppliers deserve and need our support even if their goods are imported. Amazexpress and their ilk, don’t!]
It has many functions I have yet to use, including the halves. That can be overcome by setting the middle feature to (0, 0, 0) and read plus-so-far one way, minus-so-far the other, although that will lose any prior datum setting elsewhere on the work – often, a corner or a main axis. It also has PCD and arc calculator – oh, and calculator! – among various goodies I have yet to explore in the few years since I bought it.
Its only drawback is that switching between mm and inches (not within the same work!) seems to want the whole unit turning off and back on to register, which seems wrong – but that might be my fault. I may have missed something in the instruction-book! Which I have to say is very well written, in British English, not brave attempts without proof-reading.
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Calculating pcd co-ordinates is not ever so hard though a bit laborious.
The Zeus books even include the appropriate factors. Or at least my editions do.
If you use ‘Excel’ or similar, create your own spreadsheet-calculator, using the diameter and hole-count as absolute-reference inputs. You could add further functions to give each hole’s co-ordinates from the primary datum on the work-piece.
CAD (2D or 3D) will let you plot a PCD anywhere on the item from its own centre, and obligingly gives that option of dimensioning everything from that primary datum.
As Dave says, be accustomed to what you have rather than what you think you want.
I think with careful planning you will find your apparently-basic DRO willl cover most of your milling, and the unusual rest by augmenting it with external help by calculator, spreadsheet, CAD or pencil-&-paper.
Let’s be honest – we are spoilt! A few decades ago we all had to count little marks on dials! (I still do, for small, simple operations.)