Manufacturing & engineering
Postprocessor
Definition
A CAM postprocessor converts software-neutral toolpath data into the NC code dialect and program structure expected by a specific CNC machine and controller. It maps motions, coordinate systems, tool changes, canned cycles, spindle and coolant commands, and other machine behavior into executable output.
Also known as: CAM postprocessor, NC postprocessor, post-processor
Updated
Between the toolpath and the controller#
A CAM toolpath describes where and how a cutter should move. The postprocessor writes that plan in the syntax, codes, and sequence expected by the selected machine control.
Onshape's G-code export guide describes the postprocessor as the translator between generic toolpath data and a machine's G-code dialect. Its CAM workflow requires a machine selection and exposes post settings such as block-number output before code is generated.
Why the machine match matters#
Controllers differ in supported canned cycles, tool-change behavior, work offsets, rotary-axis conventions, program headers, and custom commands. The LinuxCNC language reference, for example, documents its own RS274/NGC-based command set and modal behavior. Another controller can implement a different subset or add proprietary codes.
A postprocessor is therefore part of the machine configuration, not a generic export option. Qualify it with the exact controller, machine axes, tool changer, workholding, and shop procedure. Simulating a CAM path does not by itself validate the posted program.
Sources
Related terms
CAM
CAM is software that turns CAD geometry into toolpaths and machine instructions, such as G-code for a CNC mill or lathe. It needs clean solid geometry, and it is where problems like unreachable corners and missing tool clearance show up.
G-code
G-code is the line-based programming language family used to command CNC machine motion and state. A program can set positions, feeds, units, coordinate systems, tool and cutter offsets, spindle direction, coolant, canned cycles, and program control, with controller-specific dialects and extensions.