See that most floating Z axis use a linear rail or duall v bearings mounted to the plate that is driven by a lead screw. I love the mantra if it aint broke don't fix it, for production work this is true, however I like to try something new (I think) but do not want to waste my effort if it has been tried before.
Why not couple the motor and the lead screw with a splined coupler, allowing the additional vertical movement, thereby eliminating the need for the extra linear rail or v bearings? The entire plate assy can move up and down. The lead screw would need to sit in a bronze bushing at the bottom to allow it to travel verticaly and the motor which is fixed would support the top of the screw.
The only problem I can forsee is the extra preasure exerted on the torch tip, but I do not think that it would be substantial.
Thoughts or comments
You mentioned "torch tip". Is this a flame cutting/plasma torch cut-out machine you're referring to?