3D printer filament spool holder, fully-printable

(UPDATED 2014-10-31, details at the end of this section)
This spool holder design has a rectangular peripheral frame, supporting a filament spool's flanges on bearings or 3D-printed rollers. It is for use upright on a horizontal surface with a filament spool having intact rigid circular flanges. The design should not interfere with any filament which is below the height of the spool flanges, and if built using bearings it should have very low friction.
The spool holder is designed to use four inexpensive 608ZZ shielded skateboard bearings ($1-2 each in quantity 8 or more). 3D-printed pins are used to secure the bearings in the frame; they should be 3D-printed at precise sizes, as they are intended to be a light (hand) press fit into the 8.00mm bearing bores and the frame. A design for bearing-sized 3D-printed rollers is included as well, which should be a loose low-friction fit on the pins; although bearings are preferable, these rollers may be adequate, at an even lower cost. When rollers are used rather than bearings, they are most likely to work satisfactorily where the filament is pulled off the spool nearly straight up or generally down, rather than mostly sideways.
The designs are in OpenSCAD (SCAD files), and have a few feature switches, and are mostly parametric. To avoid binding, it is important that the spool flanges be a loose fit within the frame: 1-2mm of clearance in excess of the greatest width over the spool's flanges. Since the inexpensive 608ZZ…