Mechanical Rigidity/Lulzbot Taz4 V slot Openbuilds rework
Lulzbot TAZ 4 Vertical Upgrade using Openbuilds V-Slot and 8020 extrusion
This picture (taken from above) shows a vertical carriage held in place with V-slot rollers on solid, sturdy 8020 extrusion. Basically this ain't going anywhere. The 8020 extrusion will not be twisting, and the carriage will not be jumping up and down or rotating thanks to the V-rollers. As a result it is only the plastic that may deform under load that could potentially result in any kind of movement. However given that the parts appear to be at least 5mm thick, in practice the amount of bending should not be significant. The only dramatic improvement which could potentially be made to this design would be to turn the entire extruder around and also lift it up so that the nozzle is much closer to the underside of the 8020 extrusion.
Even without such an improvement, all the problems usually associated with rods (bending of the rods, "play" in the bearings) which are normally associated with Vertical Carriage arrangements have completely gone.