Top Free & Open Source CNC Post-Processors and Post-Processing Tools

Every CNC programmer eventually learns the hard truth: CAM does not output real G-code. Post-processors do. Most problems blamed on machines, operators, or CAM systems are actually post-processor problems. Wrong feeds, unsafe rapids, broken tool changes, inconsistent probing logic, controller-specific quirks — all of that lives in the post.

For shops running Fanuc, Haas, Siemens Sinumerik, or Heidenhain, post-processors are the translation layer between CAM intent and real machine behavior. And this is exactly where many shops are locked in, overpaying, or stuck manually editing code.

What qualifies for this list

Included tools meet at least one of the following criteria:

• allow editing or creation of CNC post-processors
• expose post logic in readable scripts or configuration files
• support industrial controllers (Fanuc, Haas, Siemens, Heidenhain)
• are free, open source, or realistically usable without paid licenses

Pure CAM systems with locked posts are excluded.

1. FreeCAD Post Processor Framework

Best for: Open, scriptable post logic for many controllers

FreeCAD includes one of the most open post-processing frameworks available. Posts are written in Python, fully readable and modifiable. Supported outputs include Fanuc-style G-code, Haas-like variants, Siemens-style syntax, and more.

What makes FreeCAD valuable is not the CAM itself, but the post architecture. You can:

• inspect exactly how every line of G-code is generated
• adapt posts to machine quirks
• standardize output across machines

License: LGPL / Open Source
Reality check: Requires Python comfort, but rewards control.

2. LinuxCNC Post Processors

Best for: Full transparency and machine-level control

LinuxCNC ships with extensive post examples and configurations tied directly to machine behavior. Even if you do not run LinuxCNC on the shop floor, its post logic is a reference goldmine.

You can study:

• axis formatting
• motion planning assumptions
• canned cycle implementations

Many shops use LinuxCNC posts as a learning and validation base for adapting other posts.

License: GPL / Open Source
Reality check: Not a drop-in solution for commercial controls, but excellent for understanding and adapting logic.

3. PyCAM Post Processors

Best for: Simple, readable G-code generation

PyCAM is an open CAM tool, but its post-processing layer is extremely transparent. G-code output is clean, minimal, and easy to modify.

Useful for:

• learning post fundamentals
• building lightweight custom posts
• understanding controller differences

License: GPL / Open Source
Reality check: Not suited for complex multi-axis machining, but excellent for fundamentals.

4. CAMotics Post Handling

Best for: Verifying post output correctness

CAMotics is not a post-processor editor, but it plays a critical role in post validation. It allows you to simulate and inspect the actual G-code produced by your post.

This helps catch:

• wrong plane selection
• unsafe rapids
• incorrect feed modes
• missing tool changes

License: GPL / Open Source
Reality check: Use it alongside post editing tools, not instead of them.

5. NCNET / Heidenhain

Best for: Understanding Heidenhain-style post logic

Heidenhain posts differ radically from Fanuc-style G-code. Community-shared examples and open references (often used with FreeCAD or LinuxCNC) provide insight into:

• conversational cycles
• plain-language commands
• coordinate logic

While not a single tool, these resources are critical for shops running TNC controllers.

License: Open documentation / mixed
Reality check: Heidenhain posts are harder to generalize, but open references help avoid vendor lock-in.

6. PostHASTE Legacy

Best for: Learning classic post structure

Although PostHASTE itself is legacy software, many shops still reference its logic and documentation to understand traditional post construction patterns.

Useful for:

• studying how posts evolved
• understanding controller expectations
• maintaining legacy machines

License: Legacy / educational use
Reality check: Not modern, but historically valuable.

7. Fusion-Style Open Post Scripts

Best for: Practical Fanuc / Haas customization patterns

While Fusion itself is not open source, many community-published post scripts are. These scripts illustrate:

• probing logic
• tool change safety blocks
• work offset handling

Studying these scripts helps shops replicate behavior in open frameworks.

License: Varies (often permissive)
Reality check: Use for logic inspiration, not dependency.

8. G-Code Templating via Python/Jinja

Best for: Custom, CAM-agnostic post workflows

Some advanced shops bypass traditional posts entirely for repeatable work. They generate G-code using Python templates tied to part parameters.

This approach works well for:

• fixtures
• probing macros
• standard operations

License: Open source tooling
Reality check: High control, but requires strong internal discipline.

9. OpenPost / ISO G-code Post Templates

Best for: Shops standardizing Fanuc-style output across machines

Many machine shops quietly rely on generic ISO G-code post templates maintained in GitHub repos, internal wikis, or community forums. These are not tied to a single CAM system and are often used as a baseline reference.

They typically define:

• safe start blocks
• tool change structure
• coolant and spindle logic
• coordinate system handling

These templates are often adapted into FreeCAD, PyCAM, or custom Python-based posts.

Why it matters:
This approach lets shops normalize output across different CAM systems and machine generations.

License: Usually permissive / open
Reality check: Not turnkey, but extremely practical when standardization matters.

10. NC-Code Parametric Macros (Fanuc / Siemens)

Best for: High-repeat parts, fixtures, probing routines

Some shops skip traditional post-processors for specific workflows and instead rely on parametric G-code generators built around controller macros.

Typical use cases:

• probing cycles
• fixture offsets
• drilling patterns
• repeatable machining logic

These generators are often written in:

• Python
• simple CLI tools
• spreadsheet-driven scripts and then expanded into controller-specific macro calls.

Why it matters:
This gives total control over output and removes CAM dependency for repetitive operations.

License: Open (user-authored tools)
Reality check: Powerful, but only viable with disciplined programmers.

Post Processing Tools Comparison

How shops actually use these tools

Most successful shops do not rely on a single post tool.

A realistic workflow looks like this:

• use an open post framework (FreeCAD or custom scripts)
• validate output in a G-code simulator (CAMotics)
• standardize safety blocks and macros
• version posts like source code

This eliminates constant manual edits and operator guesswork.

Final Thoughts

Post-processors are the most underestimated part of CNC software stacks. They determine safety, repeatability, and operator trust. When posts are locked or opaque, programmers compensate by editing code manually — every day. Free and open-source post-processing tools remove that dependency. They allow shops to own their machine logic, adapt to mixed controller environments, and scale without multiplying errors.

About MDCplus

Our key features are real-time machine monitoring for swift issue resolution, power consumption tracking to promote sustainability, computerized maintenance management to reduce downtime, and vibration diagnostics for predictive maintenance. MDCplus's solutions are tailored for diverse industries, including aerospace, automotive, precision machining, and heavy industry. By delivering actionable insights and fostering seamless integration, we empower manufacturers to boost Overall Equipment Effectiveness (OEE), reduce operational costs, and achieve sustainable growth along with future planning.