Some confusion about the free end of a Z axis lead screw became apparent on the CETUS2 Kickstarter forum when the printer backplate was shown removed. The intuitive reaction from some members was the end bearing was missing.
I’ll get to the point. The free end Z axis lead screw is NOT a problem as far as function. It is a BEST-PRACTICE (in this application) to not have a fixed bearing at the non-driven far end. Light weight lead screws this length are seldom PERFECTLY straight, but are functionally straight. They need slight wiggle room at that far end.
On some CNC and 3D print machines with exposed screws, the end will be protected from deflection by a NON RESTRAINED free floating bearing. Just in case the exposed screw is impacted by flying debris or user contact action. Concealed screws need no such deflection guard.
My Anycubic Vyper has two exposed Z axis screws with floating deflection guards on the ends. As do my two Geeetech 3D printers. I can grab the free ends and they will slightly wiggle.
A rigid bearing on the non-driven end is not a “better” design. However, some heavy duty machine tools (like a metal cutting lathe) will have substantial bearings on both ends of their (also substantial) lead screws. They must deal with high thrust loads and are often *driving from both ends*. (Manual and power feed)
On the CETUS2 without the backplate, the Z axis screw is far too exposed to accidental contact and deflection bending. An end deflection guard is an extremely good idea. With the backplate in place there is some protection for the screw. A user could print a top deflection guard bracket and attach to the backplate.
CETUS should consider adding this deflection end guard. It isn’t necessary for normal (no touch) operation. Professional operators know this. But the screw is still accessible to any and all user contact and perhaps become damaged when moving the machine and grabbing the wrong part. The copious grease on the screw is a clear no-touch deterrent to most aware users.
Now you know. Far end bearing not required, but a far end deflection protection guard is good practice when the screw is accessible.