Itty Bitty Double Extruder

[printbus]

Properly tightened, the eight M5 bolts that hold the X-motor and X-idler plates to the horizontal v-rails turns the x-carriage into a pretty firm assembly. The z-rods can really only be used for minor adjustment once those M5 bolts are tight. As csader is seeing, you can't use a z-rod to pull down one side very much without the nut pulling out of the bracket on that side. The nut is intended to back out like that in case of a failure that causes the Z-motors to attempt driving the extruder into the print bed. Here, it's the other side of the x-carriage being held up by the other Z rod rather than the extruder hitting the print bed. Different cause, same result.

EDIT 4: Removed portions of the post that were a bad idea...