Spheremill (2014)

DIY 3 Axis CNC milling machine for spherical object fabrication

Spheres or spherical forms in digital fabrication are typically approximated within a Cartesian coordinate system. A clear example of this approximation is seen in 3D-printed spheres, where distinct layers become visible near the poles. Cartesian coordinate machines generally require a minimum of four degrees of freedom, and ideally five, to process geometries that are perpendicular to the spherical surface. However, machines capable of performing this task are often prohibitively expensive for individuals or small fabrication labs, especially when the object exceeds 300mm in diameter.

Inspired by MIT's Center for Bits and Atoms’ MTM Snap project and the Eggbot from the Evil Mad Scientist Lab, Spheremill addresses this issue by introducing a spherical coordinate system. The prototype uses THK R-guides and a belt-drive mechanism to move the spindle along the polar angle (θ). Two rotary axis modules are employed for the azimuthal angle (φ), providing sufficient torque for processing the stock. The machine can handle spherical stocks up to 550mm in diameter with a maximum processing depth of 150mm.

The chassis is primarily constructed from 12mm high-density polyethylene (HDPE) sheets, utilizing a snap-fit joint design inspired by the MTM Snap, which reduces the need for tedious bolting while maintaining assembly accuracy. The total material cost is approximately $1500, though this could be reduced significantly by replacing the R-guides with a DIY solution.