How to Source CNC-Compatible Models for Subtractive Manufacturing

CNC machining with the Carvera and Carvera Air opens up a world of possibilities for creating intricate and functional parts. However, before you can start milling, you need the right models to import into CAM software. There are two main ways to get projects and files: designing your own models using CAD software or downloading existing ones from file-sharing platforms.

If you want complete control over your projects, designing your own models in CAD (Computer-Aided Design) software is the best approach. Programs like Fusion 360, SolidWorks, and FreeCAD allow you to create precise 3D models tailored to your needs. When designing for CNC machining, keep the following factors in mind:

• Ensure that the model is CNC-friendly, meaning it can be cut with rotary tools instead of built layer-by-layer like a 3D printer.
• Avoid overhanging features that cannot be milled without special setups.
• Avoid internal features that cannot be reached with a cutting tool.
• Consider tool access and machining strategies, especially for 4-axis milling, which allows for more complex geometries.
• Design with the material in mind. Some materials can lose rigidity when machined, which may cause models to deform.
• Design with work holding in mind, as the part needs to be supported until the finishing processing stage.
• You can also modify existing downloaded models that may not be CNC machinable.

For reference, here is a quick comparison of common CAD tools:

For those who want to start milling quickly, file-sharing platforms provide ready-made models:

• Thingiverse – Primarily for 3D printing, but some models can be adapted for CNC machining.
• GrabCAD – A vast library of engineering and manufacturing-focused models.
• Instructables – Offers not only models but also step-by-step guides.
• CNC-specific repositories – Some websites focus on CNC-ready files designed specifically for milling.

When you browse these platforms, do not just look at the shape of the model. Pay attention to:

• The original manufacturing method the designer had in mind (3D printing, laser cutting, or machining).

• Whether the designer mentions tool diameters, minimum wall thickness, or fixturing in the description.

• The file formats provided (for example, STEP files are usually easier to adapt for CNC machining than STL files when you need to modify features).

We are also in the process of developing our own project-sharing platform, where you’ll be able to access models optimized for the Carvera and Carvera Air machines. This platform will include detailed instructions to ensure a seamless machining process.

Not all 3D models are suitable for CNC milling. Here’s how to differentiate them:

• 3D Printing Models: These are designed for additive manufacturing, meaning they often include features like thin walls, overhangs, internal features, and enclosed structures that CNC machines cannot easily create. (Keep in mind that you can modify a 3D printing model in CAD software to make it CNC machinable.)
• CNC Machining Models: These are optimized for subtractive manufacturing, meaning they are designed to be cut from solid material and machinable with rotary tools.
• 3-Axis vs. 4-Axis Models: Simple parts with flat features or reliefs without overhangs can be milled on a 3-axis machine, whereas 4-axis machining allows for more complex angled geometries, such as cylindrical or rotational relief cuts with some undercut features.

The table below summarizes the main differences between typical 3D printing models and CNC machining models:

Our CAM (Computer-Aided Manufacturing) software, MAKERACAM, supports a variety of file types:

• Images (JPEG, PNG, SVG, BMP) – Convert 2D images into engravings or vector-based tool paths.
• 2D Files (DXF, SVG) – Used for cutting or engraving designs.
• 3D Files (STEP, STL) – Used for milling solid models in either 3-axis or 4-axis operations.

When working with CNC machining, material selection plays a significant role in the final outcome. Materials like wood, acrylic, aluminum, and brass all behave differently under a CNC tool. For example, softwoods may require different feed rates and tool paths than metals to avoid chipping or burning.

The table below gives general tendencies you can use as a starting point when planning toolpaths for different material types:

Additionally, CNC machining requires careful planning of tool paths to ensure the most efficient cutting process. Using CAM software, you can generate efficient tool paths that consider cutting depth, step-over, and spindle speed to optimize machining performance and extend tool life.

By leveraging these sources and understanding CNC-compatible models, you can make the most out of your Carvera or Carvera Air machine. Whether designing your own projects or using shared models, the possibilities for precision machining are endless!