Llavero Cubo

A cube with a free-floating sphere trapped inside — a pocket-sized 'impossible object' on a keyring. *Llavero cubo* means, simply, cube keychain, and that's the clever trick here: a rounded cube is bored with a big circular hole on each face, and through those windows you glimpse a smooth ball rattling loosely inside the shell. The sphere is larger than any single opening, so it can never come out — it looks impossible, yet it prints in one piece with no assembly. A small hole through one corner takes a split ring or lanyard. Rendered in glossy gold here, it reads as a fun fidget-y trinket you can spin and roll between your fingers. Great as a stocking filler, maker-fair giveaway, party-bag novelty or a quick print to show off what 3D printing can do to the uninitiated. Print notes • The magic depends on clearance: the captive ball is modelled with a gap so it releases from the shell — do not scale the sphere and cube separately. • Print in place, no supports, with a raft off; a slightly higher wall count keeps the openings from sagging. • Slow the first few layers around the ball so the bridging over the lower holes stays clean. • Snappy in a single colour, or run a filament change so the inner ball contrasts with the cage. • Add a jump ring through the corner hole and it's ready to clip to keys or a bag.