Despite growing interest in multi-colour FDM printing, current methods remain limited by hardware complexity, material waste, and the inability to produce smooth gradients. This research investigates a novel method for multi-colour printing using a single nozzle combined with dual-colour and triple-colour filament, with controlled rotation, to influence perceived colour blending and transitions.

A standard Ender 3 printer was modified to include a rotational B-axis, with hardware enhancements such as a slip ring and belt-driven stepper motor to reduce torsion and nozzle deviation. Custom G-code was generated via Grasshopper, linking image-based colour data to nozzle rotation angles, allowing for systematic testing of smooth gradient and snappy colour switch performance. Extensive testing was conducted on 2D and 3D samples to evaluate the effects of parameters such as rotation angle, step size, speed, and print direction on colour reliability and gradient quality.

The results demonstrate that nozzle rotation can produce smooth gradients and snappy colour switches without purging, with reliable reproduction of the base colours and limited success with intermediate colour filaments. Mechanical factors such as nozzle deviation and filament torsion still affect reliability, but calibration and passive settings can reduce these effects significantly. These findings position rotational nozzle systems as a promising third category in multi-colour FDM printing, combining expressive colour control with relatively simple hardware adaptations and low waste.
.