Thanks Gents,
It will be a while before I can comment on much of this, but….

I had not included a release in my Z axis, which is similar to Robins (but not as pretty … no surprise there!), so you have saved me from myself, and a time consuming re-make. (two Hobgoblins).
I am using a smaller motor for the Z, as it will be geared and therefore should be approx. the same torque ( although slower).

Irving (Hi ), said you would not use a boring tool on a CNC, why not?

I don’t have one and have been cutting large holes using a mill and my rotary table, but I would have thought that having a fine a constant feed down would be beneficial, giving a more accurate (round) bore, with a better finish, would you enlighten me?
I remembered watching a program on TV, where a company building Drag Racers had received a part with a bore (about a foot across) cut in it, which was not round.
The chap commented that it must have been cut using a CNC machine (and therefore circular interpolation).
I am concerned that my bores for the Z bearings will not be very accurate, so I was intending to buy a boring bar.

I have just received my MT3 collets today, so haven’t tried them yet.
I use an Osborn Titanic collet chuck, which seems quite sturdy, so I will compare the cuts with the collets and see how much difference there is.

It seems that we have the wrong spindle for CNC, are we stuck with it? The R8 is presumably not any different in operation.
I guess the proper CNC machines have much larger quills, allowing the larger tapers to be used, is the lower bearing the limiting factor?

Cheers for now.
Mark