Screaming Skull – Pull-Rod Siren with a Bone Through the Head

Grab the bone, yank it through the skull – and it howls! A hidden siren inside spins up while the teeth rattle. Push the bone back and do it again. Fully 3D printed: no screws, no bearings, no supports – just a little glue.

HOW IT WORKS The bone is a gear rack that runs straight through the jaw joints. Inside the skull sits a small centrifugal siren: pulling the bone spins a 12-tooth pinion on the rotor, the rotor flings air through 12 ports in the stator ring – that chopped airflow is the howl. - At the end of the stroke the rack has a toothless gap, so the rotor spins down freely and the howl fades out

- Air is sucked in through the eyes, nose and blown out through the teeth

- An internal 45° "tent" wall separates intake and exhaust (prints without supports)

- The bone cap on the other side stops the bone, so it always stays in the skull

PARTS (7 printed parts) 01_Gehaeuse – siren housing with axle 02_Rotor – siren rotor with pinion 03_Deckel – lid (8 crush ribs, press fit) 04_Knochen – the bone (gear rack) 05_Knochenkappe – bone end cap 06_Bodenplatte – base plate with holding tabs 07_Schaedel – the skull YOU ALSO NEED - Glue (super glue gel or 2-component epoxy) for the base plate and the bone cap

PRINT SETTINGS Material: PLA (no silk PLA), PETG maybe also works (only tested it with PLA) Supports: OFF for all parts – all files are already oriented, don't rotate them Skull: use a Brim for better Bed Adhision Setting: 0.15mm Balanced

Printed on a Prusa Core One + (Gen 2) ASSEMBLY 1. Put the rotor on the axle of the housing, press the lid on until it sits flat. The rotor must spin freely (for better spinnig i used some oil). 2. Place the siren unit into the ring on the base plate. Turn it until the rack channel lines up with the holes. 3. Put the skull over it – face to the front, the jaw joints over the tabs. 4. Push the bone through the skull. 5. Press the bone cap onto the toothed. 6. Test everything: pull, let it howl, push back. 7. Glue: take the cap off and the bone out again, lift the skull, put a thin line of glue on the rim of the base plate, set the skull back on and let it cure. Then insert the bone again and glue the cap onto the toothed end. Note: once glued, the siren unit and the bone can't be removed anymore – so test first!

HOW TO USE Hold the skull with one hand and pull the bone quickly and firmly all the way.