Spool Puck: sealed twist-lock dry box for filament spools (TPU seal, optional hygrometer window)

What it is

I set out to make a new filament spool container design that was better than the designs I could find. Something made of fewer parts, to increase durability and deliver a reliable seal. Something easy to print and easy to assemble. Yet something efficiently sized, that didn't waste material to print.

This is a round box for one filament spool with a lid that twists shut. The lid and the body can each print on one 256mm plate, with a third plate that's a TPU ring to make the seal, and a fourth for two label cards. A fifth plate is the same lid without the hygrometer window: print one lid or the other. A sixth plate is an optional extra: the same body in PETG Translucent, instead of plate 1. It lets you see a little of what is inside, but only a faint sense of the spool's colour comes through.

The lid has six small tabs inside its rim; the body has six ramps on its outside wall. Drop the lid on with the arrows lined up and turn it clockwise about 12 degrees to close: the tabs ride under the ramps and pull the lid down 1.5 mm onto a soft TPU lip ring that sits in a groove on the body rim. The lip folds flat under the lid roof, so the seal has no screws, no gasket to glue, and nothing to lose.

Also in the lid: an optional window for one specific mini LCD hygrometer (Amazon B0CJM5R5N6, the 49 x 29 x 15 mm type with spring clips on its short ends; the window was sized from caliper measurements of that unit and test prints, and no other hygrometer is supported; if you don't want one, print the lid without a window, which has a plain solid roof and is otherwise identical), 36 shallow grip scallops around the rim so it turns easily, and six small keeper lugs that hold the label card down. The body has a slot on its side for a 60 x 24 mm label card, which you print flat on a smooth plate so dry-erase marker wipes off it. Two runners under the body let the puck stand on its edge.

Size

• Closed puck: 239 mm across, 95 mm tall.

• Takes spools up to 210 mm across and 74 mm wide (a standard 1 kg spool with room to spare).

• Desiccant: there is no built-in holder. A loose desiccant bag or a small jar fits in the ring of space around the spool (about 10 mm all round for a 200 mm spool).

Parts you print

• 1. Body. Material: Bambu PETG Basic, white (any PETG). Plate type: Textured PEI, no glue. Notes: 5 mm brim. 233 x 235 x 90 mm.

• 2. Lid with hygrometer window. Material: Bambu PETG Translucent (clear). Plate type: Smooth High Temp plate, thin wipe of glue stick. Notes: Prints roof down, so the roof face comes out glossy. 239 across, 23 tall.

• 3. Lip ring. Material: Bambu TPU 95A. Plate type: Textured PEI, no glue. Notes: 0.2 mm layers (set in the file). Dry the TPU first.

• 4. Two label cards. Material: Any PETG, your choice of colour. Plate type: Smooth High Temp plate, glue stick. Notes: Glossy face down. 60 x 24 x 1.2 mm.

• 5. Lid without window (print instead of plate 2). Material: Bambu PETG Translucent (clear). Plate type: Smooth High Temp plate, thin wipe of glue stick. Notes: Same lid with a plain solid roof. Same size and settings as plate 2.

• 6. Body in PETG Translucent (optional, print instead of plate 1). Material: Bambu PETG Translucent (clear). Plate type: Smooth High Temp plate, thin wipe of glue stick. Notes: Same body as plate 1. 5 mm brim. Shows only a faint hint of the spool's colour.

Nothing else is needed: no screws, no magnets, no inserts. The hygrometer is optional: one mini LCD hygrometer, Amazon B0CJM5R5N6, only for the lid with the window.

Print settings (what the 3mf already contains)

Sliced for the Bambu Lab X1C with a 0.8 mm nozzle at 0.4 mm layers, OrcaSlicer profiles "0.40mm Standard @BBL X1C 0.8 nozzle". Walls are designed as whole numbers of 0.82 mm lines (rim 3 lines, scallop bottoms 2 lines), so the slicer lays clean perimeters with no gap fill.

• 1 Body. Filament slot in the file: 2, PETG Basic. Bed: 70. Nozzle first layer: 245. Nozzle after: 255

• 2 Lid. Filament slot in the file: 4, PETG Translucent. Bed: 80. Nozzle first layer: 260. Nozzle after: 245

• 3 Lip ring. Filament slot in the file: 1, TPU 95A. Bed: 35. Nozzle first layer: 230. Nozzle after: 230

• 4 Cards. Filament slot in the file: 2, PETG Basic (change to any PETG). Bed: 70. Nozzle first layer: 245. Nozzle after: 255

• 5 Lid without window. Filament slot in the file: 4, PETG Translucent. Bed: 80. Nozzle first layer: 260. Nozzle after: 245

• 6 Translucent body. Filament slot in the file: 4, PETG Translucent. Bed: 80. Nozzle first layer: 260. Nozzle after: 245

Both lids and the cards are set to 100 % infill with 10 top and 10 bottom layers, so the clear parts are fully solid: sparse infill shows through translucent PETG and spoils the look. The translucent body is solid only where you look through it: 3 walls make the 2.46 mm wall exactly three solid lines, and 6 bottom layers make the 2.4 mm floor solid; the thick legs, spool rest, rim and ramps keep the normal 15 % infill. In another slicer, use the body STL with those two settings. Check the plate-type tab on plates 2, 4, 5 and 6 before slicing (they should read High Temp Plate; the rest Textured PEI).

Not tested: a 0.4 mm nozzle. The STLs will slice at 0.4, but the wall thicknesses were chosen for 0.8 mm lines, so expect gap fill in the 2.46 mm rim and check the ramps' 45 degree undersides print cleanly. If you try it, say how it went in the comments.

Assembly (five minutes)

1. Lip ring: lay it in the groove on the body rim, with its thicker foot down in the groove and the thin lip leaning inward, toward the centre. It seats with a little nudging. Optional: a few dots of superglue in the groove (never on the lip) before inserting the lip ring, and then hold the lip ring in place for a few seconds while the glue sets. If you glue it, leave the lid off for a full 24 hours; superglue fumes leave a white haze on clear PETG inside a closed box.

2. Hygrometer (optional, lid with window only; the B0CJM5R5N6 unit above): push it into the window from the outside of the lid until the bezel sits flat. The two spring clips on its short ends click out behind the 4 mm end walls. It is held by those clips; to remove it, squeeze the clips from inside.

3. Label card: with the lid off, slide a card down into the slot on the side of the body from above. Its own spring holds it; the lid's keeper lugs sit over it when locked.

4. Lid: match the small raised arrow on the lid rim with the one on the body wall, drop the lid on, turn clockwise until it stops (about 12 degrees). To open, turn back and lift.

What is proven and what is not

• Proven: I've printed a number of these on a Bambu X1 Carbon and they work very well in my tests. The twist lock, the window (size J latches the hygrometer above), the seal (the lip folds flat, the lid pulls down evenly), and the lid with scallops and keepers have all been printed and work.

• Printed on the sister design (the TPU Feeder Puck, same wall, same slot): the label card holder and the cards. The card fits well and the holder lips print cleanly.

• Still waiting to see how this lasts over months. The hygrometers in my own pucks are an ongoing test, and so far the seal is much better than any printed spool case I have used before.

• Not supported: any other hygrometer. The window fits the one unit above and I will not be measuring others. If yours is different, print the lid without a window, or edit the STL: the window is a simple rectangle through the roof.

• Printed: the translucent body. It prints well and looks nice, but translucent PETG is not very see-through, even from a very good print: you get a slight, very faint sense of the spool's colour, nothing more. Treat it as a small extra, not a window.

• Not printed yet: the lid without a window. It is the proven lid with the window filled in solid; everything else on it is unchanged.

• Not tested: 0.4 mm nozzle, other PETG brands, other materials.

What could go wrong

• The lid is a big flat clear print. Glue stick on the smooth plate is there to stop it sticking too hard, not to help it stick. Let the plate cool fully before lifting.

• Clear PETG on a 0.8 nozzle: a faint stripe may show along the bottom of each grip scallop where the wall is thinnest. Cosmetic only; the lock is on the inside of the rim.

• Printed holes come out small at 0.8. The window is sized from prints, not from the drawing; a different slicer or filament may shift it a tenth of a millimetre, which is about the whole margin the hygrometer's clips allow.

• TPU 95A prints the ring at 0.2 mm layers. Wet TPU prints stringy and the lip will not be smooth. Dry it first.

• The translucent body will not show you the spool's label or how much filament is left.

• The lid pulls down hard onto the lip. If the lid will not turn to the stop with the ring in, check the ring foot is fully down in the groove all the way round.

Design notes

Own design, written as a parametric script, not a remix. All undersides on every part are 45 degree chamfers so there are no supports anywhere. The body is printed floor down, the lids roof down, all flat on the bed.

Companion design by the same account: TPU Feeder Puck + Slack Case (this puck turned into a bearing-mounted desiccant dry box that feeds TPU to the printer, with an experimental case for the TPU the printer backs out).