All of those thermal tests on the MK5 head gave me plenty of time to ponder the problem of what to do with the filament bundle. Thingiverse has many plans for spools that fit over, under, or beside the printer, but they all seemed complex and fiddly. Besides, I didn’t have the printer running yet, so I couldn’t print up the parts… much less laser-cut anything.
The Parts Heap disgorged a 4-inch Lazy Susan bearing, some double-layer corrugated cardboard, and odd bits of wood. The end result fits neatly atop the Thing-O-Matic printer:
The base is 2 x 3-inch (actually measuring 1.5 x 2.5 inch) lumber, cut to exactly fit between the front and back plates of the printer box. The boards also butt against the socket-head cap screws securing the printer’s side plates, so they’re not moving. A scrap of 1/4-inch plywood bridges the two; it’s held in place with hot-melt glue atop the lumber. The weight of all that wood holds the assembly in place; making it lighter might not be productive.
The filament coil rests on a hexagon of double-thick corrugated cardboard, cut about 12 inches across the flats and 13 inches across the points; you could glue two single-thickness sheets together. I laid it out with compass-and-ruler techniques, but do what you like.
The pegs are 7/16-inch wood about 2 inches tall; the outer ones are on the hexagon points and the inner pegs are on a circle 1.5 inches inside the outer pegs. The rectangular caps on the inner pegs prevent the filament from creeping upward while feeding and are angled to let it slide off into the conduit. They’re held in place with hot-melt glue, of course, and a bit more glue stiffens the hexagon points.
The only store-bought part is the 90-degree PVC elbow originally intended for electrical work: it’s a “1/2-inch Schedule 40 Rigid Nonmetallic Conduit” elbow. I slipped a spring inside the bore to prevent collapse, applied a hot-air gun until it was flexy, bent the second right angle to align the end bell with the incoming filament, and introduced it to Mr Belt Sander to angle the entrance bell more-or-less at right angles to the incoming filament.
The Lazy Susan bearing must be centered on the top of the printer, but the hole for the conduit must be forward of center to align with the MK5 Extruder head’s filament entry. As it turned out, butting the conduit against the forward rim of the bearing (the non-rotating base part) worked perfectly. More hot-melt glue holds it in place.
This front view shows an out-of-focus peg and filament pile at the top, the Lazy Susan bearing between the plywood and cardboard, and the filament dropping straight into the MK5 head.
The spool easily rotates backwards when the extruder motor reverses. You can lift the spool off, put it down next to the printer, fiddle with the extruder machinery, then replace the spool without cutting the filament. Trust me on this, I’ve done it a lot.
If I hadn’t dropped the filament bundle, it would probably have slipped right into the spool without any fiddling; the coils are about a foot in diameter as shipped. I devoted a few minutes to feeding the greatly enlarged and somewhat tangled mess neatly into the spool, after securing the bitter end to the cardboard with (wait for it) a dab of hot-melt glue.
If I ever build another spool, I’ll replace the cardboard with either 1/4-inch plywood or acrylic, then print up some better-looking peg-like objects. A shot coat of paint couldn’t possibly hurt its appearance in the least, either…