Millability describes whether a digital design can be manufactured on a specific milling machine in a specific material. It requires three conditions: a geometrically valid data model, compliance with material-specific rules such as minimum wall thickness and edge stability, and reachability of all surfaces by the tool in the chosen machine setup. A technically flawless STL file is not automatically millable.
What does millability depend on?
On the interplay of geometry, material and machine. The same file can be millable on a 5-axis machine and unmillable on a 3-axis machine, work in PMMA and chip in glass ceramics.
Learn more: What Mill Check checks