CNC Post Processors

Custom CNC Post Processor Development: Complete Guide

A custom post processor is built around one machine, one controller and one shop's way of working. This guide walks through the full development process, from data collection to machine proving.

July 3, 20269 min readENGIMANDI CNC Team

Step 1: Collect machine information

  • Machine: make, model, type (VMC, HMC, 5-axis, lathe, mill-turn).
  • Controller: brand, model and software version, installed options.
  • Kinematics: axis names, rotary configuration (table-table, head-table, head-head), pivot distances, directions and limits.
  • Tooling: tool changer type, pre-select, maximum tools, tool length measurement method.
  • Options: TCP, tilted planes, high-speed modes, probing, through-spindle coolant, chip conveyor.
  • Sample programs: hand-written or edited programs that run well today.
  • Machine manuals: programming manual and MTB-specific M-code list.

Step 2: Agree the output specification

Sit with programmers and operators to agree the exact format: header content, comments, line numbers, tool change sequence, safe start codes, preferred cycles, rotary output and end-of-program behaviour. Write this down as the post specification; it becomes the test checklist later.

Step 3: Choose the base and language

CAM systemPost language / tools
Autodesk Fusion, Inventor CAM, HSMWorksJavaScript (.cps) with the Autodesk post engine
Siemens NX CAMPost Builder / Post Configurator, Tcl event handlers
MastercamMP language (.pst) with machine and control definitions
SolidCAMGPP language (.gpp / .mac) with VMID machine files
hyperMILL, PowerMill, Esprit, othersVendor-specific post generators and scripting

We usually start from the closest proven base post for the controller, then customise it. Writing from scratch is reserved for unusual machines.

Step 4: Develop

  1. Configure machine kinematics and limits.
  2. Implement program structure: header, safe start, tool changes, end.
  3. Implement motion: rapids, linear, arcs, rotary and multi-axis.
  4. Implement cycles, compensation, coolant and machine options.
  5. Add safety checks: limit violations, unsupported operations, missing data.

Step 5: Test with a standard program set

Post a set of test parts covering every operation type the shop uses: facing, pocketing, contouring, drilling, tapping, boring, 3+2, simultaneous 5-axis, turning and threading as applicable. Compare output line by line with the specification.

Step 6: Simulate

Run the NC code in G-code based machine simulation (for example VERICUT, NCSIMUL, NX ISV, CAMplete or Fusion machine simulation) with an accurate machine model to check motion, limits and collisions.

Step 7: Prove on the machine

1. Dry run above the part, feed and rapid overrides reduced
2. Single block through tool changes and rotary moves
3. Air cut on the real setup
4. First part with operator at feed hold
5. Fine-tune and release

Step 8: Document and support

Deliver the post with a change log, a list of post properties and options, and the test programs. Keep it under version control so future changes are traceable.

A post processor is only finished when it has cut real parts on the real machine.

Start your custom post project

See our CNC post processor development service, or read how commissioning works.

EM
ENGIMANDI CNC Team

We develop, customise and commission CNC post processors for Fusion, NX CAM, Mastercam, SolidCAM and other CAM systems.