A Software-Only Post-Processor for Indexed Rotary Machining on GRBL-Based CNCs

Affordable desktop CNC routers are common in education, prototyping, and makerspaces, but most lack a rotary axis, limiting fabrication of rotationally symmetric or multi - sided parts. Existing solutions often require hardware retrofits, alternative control lers, or commercial CAM software, raising cost and complexity. This work presents a software - only framework for indexed rotary machining on GRBL - based CNCs. A custom post - processor converts planar toolpaths into discrete rotary steps, executed through a br owser - based interface. While not equivalent to continuous 4 - axis machining, the method enables practical rotary - axis fabrication using only standard, off - the - shelf mechanics, without firmware modification. By reducing technical and financial barriers, the framework expands access to multi - axis machining in classrooms, makerspaces, and small workshops, supporting hands - on learning and rapid prototyping.