counterbalancing the spindle

[johnsattuk]

No doesn't happen and if you have the correct size motors the holding torque is enough.

If you have a very heavy Spindle then having a counter balance will help the motor but it's still down to the motor to hold it unless you have a break on the motor.

Once upon a time, many years ago I worked at a place which had a large vertical boring m/c, the spindle weighed 7 tons and was c/balanced with a large iron casting via a rack and pinion system. Apprentice left in charge wound the spindle up past the end of the rack. Felt the earth move a quarter of a mile away.