Here's my idea for a Z axis drive for an Ingentis or derivative. Again, all three axes are shortened by 200 mm to keep everything in view.
The M6x1.0 threaded rod gives 0.005 mm per whole step, but will be admittedly slow. The threaded rod is supported by 696-ZZ bearings. I didn't want to support it at both ends, but with the Z stroke I think I can get, it will be 425 mm long. The green piece carries the nut and isolates the carriage (blue) from any wobble in the screw. It's a derivative of this piece: http://www.thingiverse.com/thing:20147
The nut carrier will twist slightly on the screw with any wobble, leading to small, cyclic Z position errors. If I have any noticeable banding, and I can't straighten the screw, I'll have to come up with a nut carrier that doesn't twist with wobble.
But all that's beside the point. The point is, driving the Z axis with a screw like this gives you a simple Z axis drive that won't fall when power is lost, and there should be room for 300 mm of Z axis stroke within the standard Ingentis frame dimensions.
The pulleys for the Spectra line are 624-UU U-groove bearings. The square tube is more 10x10x1 aluminum.
It just occurred to me that the bearing at the motor end of the screw is redundant. And I have an idea now for a way to decouple screw wobble from the carriage without inducing any Z error. I'll implement that as the rest of the design matures.