"Practical" maximum size of cantilevered bed?

Just like the title states, I'd like to have a discussion in regards to bed size limitations. For the printer I'm designing, the bed size is roughly 400 mm by either 400 or 600mm with the bed being a 6mm cast aluminum plate fixed directly to the cantilever. The lifting mechanism will be a 16mm ballscrew and either 20mm smooth rods or liner guides. Does this seem reasonable, or am I being a bit optimistic?

My main concern is how much sag I'll get and how that will affect print quality. Lateral stability is also of concern.
I'm open to other Z solutions, but as I'm not using Chinese junk components, price is a factor to be considered. As an aside, I'm very opposed to the idea of more than one stepper for the Z-axis.

Any insight would be much appreciated.

Edited 1 time(s). Last edit at 04/03/2016 03:33PM by The Mechanic.

I'm working on a printer that originally had a cantilevered bed about 400mm x 400mm that was mounted to 2 smooth rods at the rear and drive with a belt drive. I was made from 4 pieces of 2040 extrusion and topped with a 1/4" cast tooling plate. It was too heavy for my motor to move it.

I ended up deciding to switch over to 3 lead screws that are driven by a single motor driven by a single belt. Still waiting on parts, but it is a proven solution for large beds so I'm pretty confident it will work.

With a large bed (ie. anything over 300 x 300), I wouldn't bother with cantilevering. It gets too difficult for a sub-optimal result.

Edited 1 time(s). Last edit at 04/04/2016 09:15AM by gmh39.

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I plan on using a rather larger nema23 motor, so I'm not worried about power.