What is the right stepper motor for the laser table?

[karl25]

Hi, my laser machine has “only” a manual controlled, driven laser table (Z-axis) with the Up and Down buttons, and I want to change that. The table has four threaded rods connected with a chain, driven by a typical standard motor (with a gear on the top).

I read some posts that others installed hybrid stepper motors, and I found lots of them, but I have no idea how strong the motor should be 3, 6, 8, or 12 Nm. What is enough, and what is the minimum? I know the strongest is always ok, but I think why should I buy, for example, 12Nm when 8Nm is perfectly adequate.

Has someone of you an idea what type of stepper motor I need and how strong it should be?

In addition to that, I saw in some youtube videos that they sometimes use the existing power units of the x-/y-axis for the motor of the z-axis. I think it is better to install a separate power unit for the Z motor.

What is your opinion?

Thanks in advance