Good suggestion regarding the weight.

For the spindle, the motor I will be using has a max speed of 8000rpm. The spindle has a max speed of 12000rpm.
I will put a 60T HTD5M pulley on the motor and a 40T on the spindle. I will still get a large amount of torque on the bottom end - 15.7N.m. I don't really imagine I would need more than this, given that the BF20 I have only has 3.6N.m. with a 1.8kw servo - and I have not managed to make a cut using all the available power yet.

As for the counterweight, originally I was going to have the counterweight slide on a round or HIWIN rail at the back of the column. With the new changes on the column I am starting to think that I may be better with a gas spring next to the ballscrew to push the column up.

Thoughts?