3D Models for CNC
Most of our customers start with 2D projects on their CNC machine. While there are an unlimited number of CNC projects that are strictly 2D, our Shapeoko CNC Router and Nomad Desktop CNC are both capable of running full 3D projects and many users eventually decide that they’d like to try something more challenging.
While we’re talking most specifically about our CNC machines, the information applies to all CNC routers and desktop CNC machines.
Here’s some preliminary information to help you get started with files for 3D CNC.
File Types for 3D Models
First, there’s nothing special about models for CNC compared to models for any other use, like 3D printing or animation. In fact, CNC software is more forgiving of funky files than 3D printers because a CNC machine doesn’t need to build up a complete object from nothing; it just needs to machine the outer surfaces.
STL files are the most common file type to save a 3D model. The STL file format began long ago as the default standard for 3D printers and over time became a reliable way to exchange 3D objects between all kinds of programs.
STL files can represent a complete object, including all sides of an object as well as internal features. While this is very useful for a 3D printer, which has access to the internal structure of a model, a CNC machine can only get to the outside of a part.
STL files represent the underlying 3D model as a series of triangles, even if the original design is from a very high-end CAD program like Solidworks. Some users think this leads to a loss of accuracy in the finished part since a series of triangles cannot fully represent a 3D model. This is untrue for a couple of reasons:
- A 3D STL can be generated to almost arbitrary accuracy and it can definitely be more accurate than your CNC machine.
- Almost all modern CAM software will convert your design to a series of triangles before creating a toolpath. The math is much to slow and error-prone to not operate on triangles.
Some 3D STL files take this triangle count to the extreme and create a MASSIVE number of triangles. This can lead to a long toolpath calculation time, a lot of memory use, and not generate a toolpath that leads to a better final product. In our experience, using more that 1 million triangles will not create a better finished product on any common CNC router. (Realistically, 250k triangles is more than enough)
OBJ files are very similar to STL in that they represent the 3D model as a series of triangles. The differences come in where the files come from, and where you can use them.
OBJ files are preferred by animation software so most of them come from 3D design programs that are made to be consumed by animation or video software; they’re not models for CNC. You’ll find that most CAM software, the software used to create a toolpath from a model, cannot open an OBJ file. While there are conversion programs available, we’d recommend that you steer clear of OBJ files and prefer STL unless there’s something very compelling about a particular file.
DXF is another long-lived CAD file format. It was developed by Autodesk for Autocad years and years ago and is widely used to move CAD files from one program to another. While it’s vastly more common to see DXF used for 2D models, it’s also capable of storing 3D models.
DXF files, both for 2D and 3D models, are widely supported by CAM software but you probably won’t find a lot of 3D models in DXF format to download. 3D STL files are much much more common.
Heightmaps and Images
Heightmaps and really more of a specialty and their use depends completely on the software that you’re using. We cover them here to be complete, but they’re usually not what people are looking for when they go searching for 3D models for their CNC machine.
A height map is basically a grid of height values that can represent a 3d objects. Because each location can only have a single height value, a height map cannot represent multiple sides of a 3D object so they are best suited to relief-style designs.
Some programs will allow you to convert an image to a heightmap, where each pixel is converted to a height based on brightness with lighter pixels being higher than darker pixels (or vise-versa).
Common uses of height maps include:
- Terrain maps
Where to Get 3D Models
Purchase a 3D Model
As CNC machines get more popular, it’s becoming easier and easier to find places to buy a model; they’re available for sale from a lot of places that were never made for digital products that you download. They have the added advantage of being made for CNC routers so they should be easy to use.
- Etsy - Search for “3D Model”, “3D STL” or “Models for CNC”
- EBay - Search for “Models for cnc”or “3d stl models for cnc router”
- Facebook groups - There are a number of model-sharing facebook groups that you can join, and many focus on CNC router files.
What Does a 3D Model Cost?
The prices of 3D models can vary greatly but, from what we can tell, most come from content creators in China and Russia. Most are priced between $3 and $50, with some sellers offering content packs with a bunch of model priced much lower. In almost all cases, they’re delivered as a 3D STL file.
Download from Sharing Sites
Free models are also widely available from sharing sites. These are generally free to download but they may not come with the rights for you to use the commercially so it’s worth looking into the details of each site or user.
How to Create a 3D Model From Scratch
Creating a 3D model is a big topic that’s better suited to its own page but we can give you a few starting points:
3D CAD/CAM Programs for Reliefs
- Carbide Create Pro
- Vectric Aspire
Both Carbide Create Pro and Vectric Aspire let you create 3D reliefs from scratch using a simplified workflow compared to full 3D CAD programs like Alibre or Solidworks. They’re literally just built for 3D modeling for CNC.
There are limitations to what you can make but, if you’re targeting a CNC router, then it’s generally a very good fit.
3D CAD Programs
Alibre and Solidworks are both what we’d consider “high-end CAD programs”. They will let you make almost anything with very high accuracy and with a great deal of control. Alibre is very reasonably-priced, given the capabilities of the program. Solidworks, by contrast, is very expensive but has wide industry adoption.
If you came here looking for “models for CNC”, these are probably not the programs you’re looking for.
How to Use 3D Models for CNC
Once you have a file you’d like to use, you need some way to convert it to a toolpath to run on your CNC router. (Hopefully, it’s a 3D STL file)
Our best recommendation is to use MeshCAM, 3D CAM software, to convert the STL file into a toolpath for your CNC router. MeshCAM makes it relatively painless to load an STL, enter your tool information, and then get gcode out.
Another alternative is to check out something like Fusion 360, which is also capable of loading STL files and generating a toolpath. Even though Fusion can do it, we have two reservations that keep us from recommending it whole heartedly:
- STL files are not really a first-class file format for Fusion 360. It’s really much better at dealing with native designs or STEP files.
- Fusion is a subscription product so you never really own it and you have to pay every year.
In spite of that, Fusion 360 is a very popular option for owners of CNC routers so it’s worth taking a look at if you don’t mind the price.
- Use STL files if possible.
- Limit STL triangle counts to 1 million triangles for best results on a CNC router.