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 bearings are only 7mm wide, each frame width is only suitable for a single width of spool. STL files are included for frames with two common widths, for 8" MakerBot spools (frame310, 3.10" inside frame width) and for 6" wiring-type spools (frame395, 3.95" inside frame width), but frames for spools of other widths or which are "virtually wider" due to warped flanges may easily be generated with OpenSCAD. Via parameters, the designs also could be customized for double bearings, or wider rollers, or to have the pin and bore diameters all in metric sizes (in case one has only metric drill bits).
UPDATE 2014-10-31
A new version of the openSCAD source file for the frame, "frameV2.scad", has been uploaded. This version has some additional functionality, selectable via additional flags in the source.
A few new ".stl" files have been uploaded; for other combinations of features or dimensions, one should expect to use openSCAD to generate customized ".stl" files for printing. Two new ".stl" files are intended to produce frames for use with MakerBot XL and XXL sized filament spools, and should be printable on MakerBot Replicator (dual) and Replicator 2-sized printers. Four other new (and more experimental) ".stl" files (with suffix "m" for Mini) are for various widths of 8" diameter filament spools, and are intended to be printable on 3D printers with small print beds, such as the MakerBot Mini. None of these frame sizes have been tested with rollers, and it is recommended that these only be built with bearings; this is due to the high spool weight of the XL and XXL spools, and due to the reduced bearing spacing to allow the small frames to be printed on 100mm printbeds.