Tubing and Board Questions

I am making sure if it would be better to use the structural/plumbing pipe that is painted black. I only ask because the emt at Home Depot is not that smooth at all. I would like to know is the Archim board good to have turn on and control the speed of the spindle and height with a z probe or is there something better that can do all that?

The EMT is better for a few reasons, if it seems really rough the zinc usually wears off really fast, or you can sand it.

All the boards are the same in that respect. All can Z probe, none can directly control spindle speed with out added parts.