Thor, or should that be Zeus?

[Chaz]

One other thing not mentioned or consdiered is weight.?

The combined weight of Spindle cartridge, motor and all that concrete will most likely require some form of counter balance. Servo alone unless large KW won't be enough I think.

My big mill has got Int40 (Same as taper BT40 with slightly different holder) spindle with 5.5Kw Inverter Motor which spins at 7500rpm and the motor alone is too heavy for one man to safely handle. The pulley alone (which uses 2 x multi V belts not HTD.!!) must weigh same as 2.2Kw spindle.

Recently I removed the head unit from column and reckon it must weigh 500kg. There is 10" sqr 3ft long Solid steel block runs down the centre of column that counter balances it. The whole thing can be lifted up/down turning the ballscrew by hand.!!

Yep, this is a valid concern. This is probably another reason why I will be a bit limited. That said, I could look at doing something to counterbalance - just adds some cost / time to the project.