4rth axis to lift/lower mill head?

I have a "homebuilt"mill that has a z-axis travel of about 2.75" via the quill. The whole mill head is mounted on a set of linear guide rails that I can raise and lower with a gearmotor, but I never really know where the head is in relation to the table.
Would it be as simple as replacing the gear motor with a stepper, and setting up another axis "A?" in the software that would allow me to raise and lower the head and know were it is in relation to the table?

Seems too easy.

Rick4004 wrote:

Seems too easy.

Yes it is.
You can also add a home switch so it homes whenever you home the machine, that way you know exactly where the table is and can lower/raise from gcode.