OpenATC

Open-source modular automatic tool changer (ATC) for hobby CNC routers, using spindle inertia for reliable collet tightening.

OpenATC is a DIY automatic tool-change system designed to be easy to build, easy to retrofit, and fully open for modification.
The system uses a unique inertia-based tightening mechanism: instead of relying on weak cams or springs, the spindle’s rotational inertia is used to lock the ER20 collet nut with a controlled, sudden deceleration.

This repository contains all CAD files, 3D-printable parts, LinuxCNC configuration examples, documentation, and sourcing information required to build your own OpenATC.

---

✨ Features

• 🧩 Modular tool holders – add as many as you like
• 🔄 Automatic tightening using spindle inertia
• 🧱 3D-printable components (designed for PETG)
• 🛠 Easy to build with common tools and off-the-shelf fasteners
• 💻 LinuxCNC-compatible with example macros included
• 🌍 Fully open-source (MIT) – build, modify, and use freely

---

⚙️ How It Works

Commercial hobby-grade ATC systems often rely on limited mechanical leverage to tighten the collet nut.
OpenATC instead uses:

• A standard ER20 2.2 kW spindle, typically at ~700 rpm
• A mechanism that brings the nut to a controlled stop
• The spindle’s rotational inertia to generate tightening torque

This results in approximately 8 Nm of tightening torque

The design is intended to be safe, simple, and replicable with common hobby CNC equipment.

---

📁 Repository Structure

OpenATC/
├─ hardware/
│  ├─ cad/          - Fusion 360 source files, STEP models, and mechanical design data
│  ├─ step/          - 3D-printable parts for the ATC system
│  ├─ drawings/     - Optional 2D drawings, DXF files, and technical documentation
│  └─ bom/          - Bill of Materials and sourcing information
│     ├─ openatc_bom.csv
│     ├─ alternates.md
│     └─ sourcing-guide.md
│
├─ cnc-config/
│  ├─ linuxcnc/     - Example LinuxCNC macros, HAL snippets, and M6 remap files
│  └─ other/        - Reserved for future controller support (Mach, GRBL, etc.)
│
├─ docs/
│  ├─ assembly.md   - Step-by-step assembly instructions
│  ├─ setup.md      - CNC configuration and integration guide
│  ├─ theory.md     - Explanation of the inertia-based tightening mechanism
│  ├─ safety.md     - Safety considerations and testing notes
│  └─ faq.md        - Frequently asked questions
│
├─ media/
│  ├─ photos/       - Pictures of the prototype and community builds
│  ├─ renders/      - CAD renders and visualisations
│  └─ animations/   - Motion diagrams or demo animations
│
└─ examples/
   ├─ gcode/        - Sample G-code for testing tool changes
   └─ projects/     - Demonstration projects using OpenATC

---

📦 Bill of Materials (BOM)

OpenATC uses a small number of purchased components such as:

• Compression springs
• Standard metric screws
• Hardened washers

The full bill of materials, along with alternates and sourcing guidance, is located in:

TBC

These parts are intentionally generic so builders can source them locally.

---

🛠 Getting Started

1. Print the step parts from hardware/step/
2. Source the bought-in components listed in the BOM
3. Assemble the ATC using docs/assembly.md - TBC
4. Install and configure your system using the examples in cnc-config/linuxcnc/ - TBC
5. Test tool changes with the example G-code in examples/gcode/ - TBC

---

🔒 Safety Notice

OpenATC intentionally uses controlled deceleration of a rotating spindle to tighten the collet nut.

Before operating:

• Always test without tooling first
• Verify spindle braking and acceleration settings
• Ensure guarding is in place during testing
• Use appropriate PPE
• Confirm that all 3D-printed parts are structurally sound

You build and use this system at your own risk.

---

🤝 Contributing

Contributions are welcome!
You can help by:

• Testing the design and reporting issues
• Improving documentation
• Submitting CAD/model refinements
• Adding controller configuration examples
• Suggesting improvements or new tool holder types

OpenATC is intended to evolve through community input.

---

📜 License

This project is licensed under the MIT License.
You are free to use, modify, and redistribute the design for personal or commercial use.
See the LICENSE file for full terms.

---

📧 Contact / Discussion

If you have questions, ideas, or build results, feel free to:

• Open a GitHub Issue
• Start a Discussion (if enabled)
• Share your build photos or improvements

OpenATC is a community-driven open hardware project — enjoy building!