Cetus Z axis clamp

Improved design see:
https://www.thingiverse.com/thing:3586841

Works much better than the original Cetus part.

This clamp design incorporates more degrees of freedom to compensate for printer manufacturing tolerances which results in a more consistent clamping force. Equally important is this approach makes two threaded stepper holes free for a Z axis brace. The Z axis shakes whenever the extruder stepper motor is accelerated and the vibrations are frozen in the print surface.

PLA makes a poor braking surface because friction causes heating and then the PLA becomes a lubricant which is followed by the Z axis crashing into the print bed.

A strip of shim brass isolates minor PLA viscosity changes. Then the compression spring compensates for any minor PLA shifting from a layer hill to a layer valley.

Print on fine with a 0.1mm layer thickness. Use a 0.4mm nozzle but choose a 0.3mm extrusion line width. The PLA is thin 0.6mm around the sprag clutch bearing to distribute th