Tiny Book Earring — a wearable book that really opens, print-in-place hinge, no supports

A book small enough to hang from an ear, and it really opens. It comes off the plate as one piece — the hinge is printed already assembled, pin and all — and there is no hardware in it beyond the ear wire you hang it from.

Closed it is 22 × 17.6 × 4.2 mm and weighs about 1.5 g. It prints in roughly 25 minutes with no supports.

What it does

Off the plate it is lying open flat, both covers coplanar. Work the hinge once to break it free, then fold the front cover over. It clicks shut on a printed detent — a hemispherical bead on one cover's rim dropping into a dimple on the other, 0.15 mm of grip. Put a thumbnail into the scallop cut in the fore edge and it pops back open.

Inside is a real page cavity, and the message ONCE UPON engraved across the inner cover, so it is hidden until somebody opens the book. Both are on the inside faces on purpose — see below.

Three things about it that are deliberate

The covers are smooth and undecorated, and they have to be. Folded flat for printing, both cover exteriors face the build plate. Anything engraved into a bed-facing face is a roof over open air, and it prints as a sagging mess. So all the detail lives where it prints face-up or on a vertical wall: the message and the page cavity on the inside, the page-line grooves and the thumb scallop on the three free edges. The exteriors come off a smooth plate looking like polished leather, which is the consolation prize.

The spine is frankly a piano hinge, not a bound leather back. A 180° fold puts both covers at the same height on the plate, so each cover can only reach the barrel at the knuckles it owns and the gaps between them are unavoidable. Seven knuckles at least make it read as the raised bands of a hand-bound spine rather than as a mistake. Hiding the hinge inside a rounded spine is possible, but it needs a mortise joint, which means two separate prints and a loose Ø1.6 pin to thread — a worse object at this size.

It hangs spine-up on purpose. The bail is a flat ring on the barrel's axis, so the hinge axis stands vertical when it is worn. A vertical pivot has no gravity torque on it at all, which means the front cover physically cannot fall open as you walk. That is why the detent only needs 0.15 mm of grip — enough to shrug off a knock, light enough to open one-handed.

Printing

The STL is already in its print orientation — place it as-is and do not rotate it. Flat on the plate, covers open.

• 0.20 mm layers, 3 walls, 20 % infill.

• No supports. Nothing in the model overhangs past 45° except the knuckle bores, which are small enough to bridge.

• Slow the first layer to about 25 mm/s. The knuckles have to bridge cleanly over the hinge gaps, and that is the one place a fast first layer bites — it is also the only thing that will ever weld the hinge shut. If yours comes off the plate stiff, work it once with a fingernail; if it is genuinely fused, your printer is laying down fatter than the 0.20 mm axial gap the hinge is built around, so slow that first layer or open pin_axial a notch.

• PLA or PETG. The pair in the photos is PETG, which holds the 0.20 mm hinge clearance without fusing and takes repeated folding better than PLA.

• Do not scale it. The hinge clearances are absolute, not proportional — scale it down and the hinge prints welded, scale it up and it rattles.

Wearing it

The bail hole is Ø2.4 mm, which swallows any standard 0.7–0.8 mm ear wire or an 8 mm jump ring. Nothing else is needed. It hangs spine-up, book closed.

Make it yours

The .scad is fully parametric and every variable is at the top of the file with a comment on what it does. The ones worth touching:

book_h / book_w 22 / 15.5 page height and cover width, in mm cover_t 2.1 one cover's thickness msg_line1/2 "ONCE"/"UPON" the engraved message msg_size 2.6 cap height - see the warning below pin_axial 0.20 hinge clearance; the one printer-dependent number n_knuckles 7 spine bands bead_r ... detent grip - raise it for a firmer click

One thing not to break: keep msg_size at 2.4 mm or above, because below that the letter strokes drop under one nozzle width and the slicer emits nothing at all rather than something thin.

Render it with:

openscad -o book.stl tiny_book_earring.scad