Well only two years later and my mill has become my primary project and I have made some progress.

I have the RMHV controller hooked up to the EM806 drives connected to the original steppers. I have also connected the home switches. I have used the original power supply and relay board for this.

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This gives me the following good things.

1) Movement on all three axis
2) Control of all three axis using either the buttons on the controller or a MPG pendant
3) Homing set up.

What isn't so good is
1) the z axis brake is errrr .... broken (I managed to loose the spring that applies the brake)
2) More of an issue is I let the smoke out of the spindle dc driver. The good news is they are still available off the shelf the bad news is they cost about 200 quid....
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I have a replacement (https://www.transdrive.co.uk/shop/pr...q-non-isolated) and I'm in the process of wiring it up.

To start with I have copied the settings (potentiometers and dip switches) from the old board but I'm now beginning to doubt the wisdom of this as the old board died on me and at some point previous to me finding it on a scrap heap someone has written the word BAD on the heatsink.

I'll need to find some info on the motor as the old board is set for max voltage of 50V which seems a bit low (ISTR Triacs go up to 180V). I'm also trying to figure out how to use the 0-10v output from the RMHV controller to set the speed as I'm not sure if I need some form of isolation between the two.

Hopefully I'm not too far from being able to cut some chips although I'm starting to think that I might be better off using MACH3/4 or Linux CNC rather than the rather limited RMHV controller.