First Inlay With a CNC

Written By Baptiste Depalle

For the first test using my newly built CNC machine, I chose to make an inlay form a simple motif. I decided to use a simple and small drawing with some sharp corners, to see how well it performs and to test the accuracy of the machine.


Converting an image into a tool-path: choosing the right software

In order to communicate with the CNC, I had to convert the jpeg image into G-code, which is the most widely used numerical control (NC) programming language, and the one I will be using to control my machine.

Penguin image used as a model for CNC inlay

There are several ways to convert an image into NC language. One can use a software like V-Carve Pro from Vectric, which can convert the image directly and gives some great results. Despite the quality of the software, it is not cheap. There are other alternative available in the open source community that are generally less user friendly but can provide good results after a bit of practice.

The first route i explored was an open source program called DXF2GCODE which is available here. DXF, which stands for Drawing Exchange Format, is a CAD data file format developed by Autodesk in 1982. Despite its age, the format is still relatively common in the CAD community. Converting a simple line image to the DXF format is fairly easy. I used Inkscape to convert the jpeg into a vector image. The vector image can be saved directly into the DXF format. My experience with DXF2GCODE was not extremely successful. The conversion into G-code works fine but it lacks the ability to control the carving process.

Finally, I settled on Fusion 360 software developed by Autodesk. It can seem like an odd choice since I have previous experiences with other CAD software like Solidworks and Solid Edge which offer similar functionalities.

I chose this software for multiple reasons.

First, Fusion 360 is not only a CAD software, it is a very complete suite that combines multiple design tools including CAD, Computer-Assisted Engineering (CAE) and Computer-Aided Manufacturing (CAM). The 3D CAD software is powerful and despite being somewhat different from other software I already know, the transition was relatively smooth.

The CAD environment can be used to do some classic parametric modeling, where the design is incremental and all objects and features are recorded in a history tree and can be modified at any time. The parts are mainly build from sketches using geometric and functional relationships. But the 3D models can also be created using explicit modeling. In this case, the geometries can be created and sculpted directly allowing for introduction of more organic, aesthetic and ergonomic features into designs. Combining the two modeling approaches will be very useful for my future projects. The CAM part of the suite is also well made and give me great control over the carving of my models on the CNC. It provides multiple tool-path strategies and gives great options to fabricate my design with the limited amount of tools that I currently have. The toolpath can be directly exported in the G-code format which I can use with my CNC.

Second, Fusion 360 offers numerous tutorials and has a very active user community. A lot of professionals are using this software but also makers and artists who offer a wide variety of innovative and original approaches to solving problems Every time I have an issue with the software or if I have some doubts about a design strategy, a quick google search will most likely give me a solution.

Finally, one of the main reasons I chose Fusion 360 is that it is basically free. Autodesk provides the software free of charge for makers using it for non-commercial applications and for students or educators.

Creating a model in Fusion 360

As for all modeling, there are often multiple strategies to reach the same goal. In this case, since I had a clean vector image, I was able to directly import it in the CAD software. I first created a simple block representing my stock piece of wood and I imported the vector image on the surface of the block. By extruding the contours of the penguin I could create a 3D representation of my final piece.

3D model of the inlay

Since I have several sharp corners in my model, I decided to use two different tools to crave the inlay. First I used a rough pass with a 1.2 mm bit followed by a fine pass over the contours with a 0.7 mm bit.

Carving the inlay with a CNC

At the time I only had ball end bits which turned out to be less than ideal. The bits were too fragile for the hard wood I used for the inlay, a block of pitch pine (Pinus rigida), and I broke several before getting an acceptable result. I should have used stronger end mills but little did I know at the time… Nevertheless, with a very slow cutting feed rate of 50 mm/min for both bits I was able to get a pretty decent inlay.

After exporting the toolpath in G-code format using GRBL post configuration, I could feed it to my CNC with Universal G-Code Sender (version 1.0.9).

Computer generated path (left) and resulting carved geometry of the penguin (right)

The carving for the inlay took about an hour to finish. As I mentioned earlier, the carving time and quality could have been increased with proper end-mills but I am still quite happy with the end result. To finish the inlay, I poured some epoxy resin mixed with black stain. Here again, for a better result, sealing the wood is required before pouring the resin to avoid some bleeding. Oh well, as they say: Practice makes perfect!

Despite a bit of bleeding of the tinted epoxy resin, the final inlay looks quite promising…

Equipment used:

Baptiste Depalle
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