Grimoire Box — a hinged spellbook with the magnets sealed inside

A spellbook that opens like a book.

Not a lid on a box — a real barrel hinge down the spine, five knuckles on the small size and seven on the large, closed by one printed pin. The cover carries blind tooling: a raised frame bead, an incised line, a diaper lattice, a sigil ring and an eldritch eye. The three cut edges are a page block — the covers stand proud of the sheets the way a binder's square does on a real binding, and the sheet lines are cut into that rebate.

120 × 85 × 30 mm (small) or 170 × 120 × 45 mm (large). Three printed parts make a complete box. No supports anywhere, no screws, no glue, no inserts.

Before you start

Filament — one colour is enough. Measured from the geometry (PLA at 1.24 g/cm³); a real slice with sparse infill comes out 10–20 % under these.

Non-printed parts — four Ø5 × 3 mm neodymium disc magnets, the same size for both box sizes. That is the entire hardware list: no screws, no glue, no inserts. The magnets are optional as well — the lid seats on the rim and stays shut under its own weight, and one switch in the source deletes the pockets and both pauses.

Tools — tweezers (the pocket is Ø5.3 mm and 3.2 mm deep, fingers do not reach in cleanly) and a marker, which is the whole polarity method below.

1 — Print three parts

Base, lid, pin. Everything prints in the orientation it is exported in — no supports, no rotation, nothing to flip.

0.2 mm layers, 3 walls, 15 % infill, ironing off on the cover face. PLA is fine for the small box; on the large one print the pin in PETG — it carries the whole lid's moment.

The cover prints art face up on purpose. That is why the lid is a separate part instead of a print-in-place hinge: a coplanar PIP hinge puts both cover exteriors on the bed, and cut art on a bed-facing face is a roof over air.

2 — Stop the printer twice and drop the magnets in

Both magnet pockets are sealed cavities. The printer stops, you drop a disc in, and the next layers bridge straight over it — so the magnet ends up fully inside the part with nothing visible in any face, nothing to glue and nothing that can be picked out.

Slice, drag the preview slider to that layer, right-click → Add Pause. Set both pauses before you start the plate. The lid's pause is four minutes into the print by design — the seal sits on the bed side precisely so a missed lid pause costs four minutes, not hours.

Polarity — the one mistake you cannot undo. Backwards magnets push the lid open, and once the bridge closes it is final.

1. Stack all four magnets. They self-arrange into the only orientation they can.

2. Mark the top of the stack and run the line down the side, so every magnet keeps a witness mark.

3. Take them off the top one at a time and drop each into its pocket marked face up — all four, both parts.

That works because the lid gets turned over onto the base, which puts its marked face away from the joint and presents the opposite pole. North meets south and the box pulls itself shut.

Press each magnet flat to the pocket floor with tweezers, check the mark, and resume. No glue: the pocket is 0.2 mm deeper than the magnet and the bridge holds it.

3 — Interleave the hinge

Lay the lid onto the base so the barrels mesh along the spine — base, lid, base, lid, base. They only go together one way round: art face up, title toward the head of the book.

4 — Push the pin in

Feed the pin in from the head end. It bottoms out on a blind bore 0.4 mm short of the far end, so it cannot fall through, and the crush ribs behind the head grip the first barrel. A firm push, not a hammer. No glue needed — a dab on the head makes it permanent if you want it to be.

That is the box. The lid swings past 110° and lies back against the spine. The two magnet faces end up 1.3 mm apart through the closed joint, which is a soft positive click rather than a snap.

Any word on the cover

Five lids are exported ready to print — plain, CODEX, GRIMOIRE, BOOK, NECRONOMICON — but the title is a parameter, and an included script turns any word into a lid STL plus a preview render:

./make_title.sh SPELLBOOK ./make_title.sh "MY BOOK" large

Only the lid carries art, so a new title costs one part — the base and the pin you already printed are reused.

The glyph size is solved, not guessed: the word is measured in the actual font and the size derived from the plaque width, capped at 9 mm of capital. The file refuses to render below 4.5 mm and says why — under that a condensed bold's stem falls below one nozzle width and the letters come out missing, not thin. About 14 characters is the ceiling.

Four colours, optional

The _4c files are one STL carrying five named solids: Import → right-click → Split to Parts, then assign filaments. Coordinates are exact, so each colour lands in the body rather than beside it, and the art is welded into single shells by a buried web — you assign four parts, not thirty.

lid_seal arrives as two discs, so the split yields six parts. Keep all six: they are the material that encloses the magnets, and Bambu fuses touching parts of one object so they weld into the lid underside. Give them the tooling colour by mistake and you get two visible dots on the underside.

Fewer than four filaments is fine — assign the same one to two parts. And the cost is real: the colour band spans 1.1–6.4 mm off the bed and the busiest layers carry all four, so expect 15–20 g of purge, about a third of the lid's own mass again.

If you miss a pause

Do not scrap the lid. It has two empty Ø5.3 × 3.2 mm cavities buried 0.6 mm — three layers — under the underside. Print mag_jig (~3 g, five minutes), hook it over the fore edge, and its bore sits dead over the buried pocket. Cut the skin out with a 5 mm drill turned by hand, stop the moment it breaks through, then turn the jig end-for-end for the other pocket. Glue the magnets in with a dot of CA, polarity checked against the marked stack.

A rescued pocket is 0.6 mm deeper, so the pair pulls a little softer. It costs you some latch, not the print.

Files

Three files make a box: base + lid + pin.

Parametric source

The OpenSCAD file is included and everything is a variable: size, title, title_font, use_magnets, the clearances (axial_clr, radial_clr, swing_clr), the page block (page_rebate, page_pitch, page_cut), and the multi-colour switch ink_web. Two sizes and any cover come out of one file.