Adjustable Spool Support

I started this project from tdanro's "Adjustable spool holder for the Original Prusa i3 MK2"
(https://www.thingiverse.com/thing:2122419), but it evolved into a shelf mounted unit, and
the capacity was enlarged somewhat.

This is admittedly total overkill, but I had some of the hardware already & just wanted
to learn more about putting together a more complex project in CAD.

It's designed to print with default settings and without supports (at least it prints fine
without them on my Prusa MK3, but YMMV).

The printed parts/quantities:

(1) Center.stl
(1) Center_top.stl
(1) Pinion_bottom.stl
(1) Pinion_top.stl
(1) Knob.stl
(2) Slide.stl
(2) Rack.stl
(4) Roller.stl
(4) Standoff.stl

Hardware:

(2) 8mm x 200mm shafts https://www.mcmaster.com/6112k44
(4) M8 x 1.25mm socket head bolts https://www.mcmaster.com/90128a276
(4) M8 x 1.25mm nylock nuts https://www.mcmaster.com/94205a260
(4) 8mm LM8UU