Chinese Puzzle Ball: 4 Nested Spheres Printed Inside Each Other (print-in-place, 4 colours, no supports)

The animation (GIF) shows the real motion: the three inner spheres turning inside the outer one, rendered from 36 positions that were collision-checked in code.

A Chinese puzzle ball (the classic carved "ivory ball") you can print: four pierced spheres, one inside the other, that come off the bed already nested and turn freely in every direction. Nobody can see how they got in there. It sits on an elegant turned pedestal.

Four lattices, four colours

• Outer, ivory, Ø64 mm: four-pointed geometric stars and diamonds (432 openings).

• Second, gold, Ø58.4 mm: honeycomb (306 hexagons).

• Third, blue, Ø52.8 mm: seigaiha waves, fans of concentric arcs (210 openings).

• Core, coral, Ø47.2 mm: cherry blossoms with five petals (286 openings).

• Pedestal: blue with an inlaid gold ring and a small HANMA mark. Ø56 mm, 31.6 mm tall. On the pedestal the ball stands 86 mm tall.

How it prints without supports

• The outside of every sphere only goes down to 44° below the equator (the rest is steeper than 45°). Below that, each sphere has a round opening at the bottom.

• Inside, each sphere does not have a dome ceiling: it has a 47° conical crown that touches the inner sphere. The cavity still contains a whole sphere, so the inner ball still turns freely on any axis. The crown leaves a smaller opening at the top, which is the window you look through.

• All lattice openings are convex or arch-shaped. Where their ceiling is flatter than 45° it is a short bridge (8 mm or less, most under 3 mm). No piece of material hangs downwards into an opening.

• The three inner spheres start above the bed. Each one rests its bottom rim on a thin sacrificial ring that rises from the bed through the bottom openings. The ring touches the sphere with 24 small teeth. After printing, cut the teeth with flush cutters and pull the rings out through the bottom. This is the only cleanup. Use a brim: the outer sphere stands on a 1.1 mm wide ring.

Print data (Bambu Lab A1 mini, 0.2 mm layers, PLA, ball and pedestal on one plate, 128 × 64 mm)

• 4 colours (AMS lite: ivory, gold, blue, coral): 21 h 37 min, 243.9 g. Every layer contains all four spheres, so the printer changes colour 3 times per layer. Most of that weight is purge waste.

• 2 colours (ivory spheres 1 and 3, gold spheres 2 and 4 plus pedestal): 10 h 14 min, 120.0 g.

• 1 colour, like a real ivory ball: 4 h 05 min, 53.2 g. Three 3MF files are included.

How it was checked

• Radial clearance between spheres is 0.6 mm. At print position, every pair of bodies (spheres and sacrificial rings) has 0 mm³ overlap and is at least 0.600 mm apart. Control: with a 0.1 mm clearance they fuse.

• Free rotation: 24 random sets of rotations of the four spheres gave 0 mm³ collision and at least 0.59 mm clearance. Control: a naive "teardrop" sphere with a 45° cone underneath hits the outer sphere when turned 90° (775 mm³).

• Trapped: the largest opening of each sphere (Ø46.0 / 42.0 / 38.0 mm) is smaller than the sphere inside it (Ø58.4 / 52.8 / 47.2 mm). Each inner sphere was moved 2.1 mm in 26 directions × 2 orientations: it hit the outer sphere every time (0 free moves out of 52). Control: with the bottom opening raised to 10° below the equator, the sphere gets out.

• No supports: each body was cut into 0.2 mm layers. Every island in every layer rests on the layer below. Control: without the sacrificial rings, the inner spheres start in mid-air. Every overhang steeper than 45° is a bridge of 6.9 mm or less. Control: a dome ceiling gives a 38 mm overhang. Lattice walls are at least 0.80 mm and openings at least 0.97 mm wide.

• Nothing floats: each colour is a single piece that touches the bed.

• See-through: radial rays with random rotations pass through the outer sphere 51% of the time, the gold one 66%, the blue one 62% and the coral one 36%. The coral core can be seen through all three outer spheres in 13% of directions.

• The ball rests in the pedestal cup at any orientation without touching the foot. No colour overlaps another.

About this design

Designed with AI assistance and checked in code before release (see above). Pictures are 3D renders and the slicer preview, not photos. Not printed yet: makes and feedback are very welcome.

Español

Bola china de marfil imprimible: 4 esferas caladas (estrellas, panal, olas seigaiha y flores de cerezo) que salen ya una dentro de otra y giran libres, sobre un pedestal. Sin soportes: solo tres anillos de sacrificio que se cortan. 4 colores: 21 h 37 min y 244 g; 1 color: 4 h y 53 g.

العربية

كرة صينية مخرمة قابلة للطباعة: أربع كرات مثقبة بزخارف هندسية (نجوم، خلية نحل، أمواج، أزهار الكرز) تخرج من الطابعة متداخلة وتدور كل منها بحرية داخل الأخرى، على قاعدة أنيقة. بلا دعامات، فقط ثلاث حلقات صغيرة تقطع بعد الطباعة.