A friend is building a CNC table for his plasma torch. The stuff for the X and Y axis will be purchased as kits.

He was wondering if I could build a Z axis controler (torch height controller).

The torch needs to be positioned away from the work based on the current flowing through the torch to the work.

Some other means of measuring the torch to work distance would prevent the controller from slamming the torch into the work.

On the surface this seemed to be a workable project.
What do you think ?

The folks at Plasmacam make tables for plasma torches. You might take a look at their design and see how they do it. Torch height is certainly done via software controlling the Z-axis, but I don't know if they use any type of feedback to do this.
Jeff

It does, they call it Digital Height Control™

It adjusts the height based on the voltage between the tip and the work. Not the current as I said in my OP.