top mounted ballscrew, would it work properly ?

[m_c]

Each ball screw will give you a single direction of travel so unless you are only intending on cutting straight lines you are going to need at least 2 axis of linear actuation. 3 axis if you want to vary your depths of cut.

I suspect what Rory meant, was only having a single central ballscrew on the long axis, instead of twin ballscrews with one either side, not an entire machine that runs on a single ballscrew.