Hi,
why bother? Is your Z axis particularly heavy? The whole point of having a ballscrew is to convert a small torque exhibited by the servo/stepper and have that translate into a much MUCH
greater force, albeit at a slower speed.

A 5mm pitch ballscrew (note: does not depend on diameter) will exert 1250N (125kg force) of thrust for every 1Nm applied.

My 750w Servos are rated at 2.4Nm, so even if my Z axis including spindle and headstock weighs 125kg, the about 1/3 of the servos torque is required just 'to hold it up' but leaves another 1.4Nm to
accelerate it.....more than enough. I am in the process of fitting a new spindle (3.5kW, 380VAC, 40,000rpm) weighing 22kg, and another 12kg for the mounting block Over the next month or so I hope to have cast (in grey cast iron) a new
headstock which will weigh 50kg. That will bring my Z axis weight to about 94kg including the Z axis saddle, scarcely enough to even bother my Z axis servo. I do not have a counterweight or
gas springs at the moment and neither do I plan on having them when I fit my new spindle.....any day now!!!

The spindle monitoring, air solenoids and circulation pump are nearly done.

Craig

PS: Correction, just had a phone call to tell me that the 24VDC coils for the Seal Air and Taper Blow air solenoids have arrived from Auckland......so all the bits I need to fit my new spindle are done.
Been a long time coming, had a real battle and hiccupp with NZ Customs (my fault) when the spindle came into NZ, and there is always other new bit to buy!!!!