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Fusion 360 for 4 axis CNC Foam Cutters

For some time I’ve been wondering if I could use Fusion 360 to generate g-code for a 4-axis hot wire foam cutting. Unfortunately, AutoDesk doesn’t include foam cutting in the Manufacturing section. I’ve had a request in the AutoDesk forum for several years but never received any response from them.

Parallel Cuts Only

So is there any way to use Fusion for foam cutters? After some pondering, I thought if I just copy the X and Y axis on a 3 axis router type cut to the U and Z. I could use the cutting option in the manufacture section to generate g-code. The original Z-axis would just be ignored.

If you are fairly handy with a text editor search and replace functions you could do this to the g-code generated from Fusion. I did try this and it does work but is prone to fat finger mistakes.

The cuts produced are just parallel cuts, so the U and Z just follow the X and Y path, but this will still be useful for some foam cutting jobs. So to reduce the fat finger mistakes we need a post processor which I will explain in the next section

Post Processor

In the Fusion 360 Manufacture section, you can create tool paths from the geometry you have designed. Although g-code is pretty much universal across different CNC machines, not all g-codes are implemented. A lot of m-codes are very much dependent on the type of machine

So the job of the post-processor is to make sure the codes are correct for your machine. That’s probably oversimplified but hopefully, you can see why we need them.

Fortunately, AutoDesk who make Fusion 360 has made these available to customize. Many more can be downloaded from the HSM library, and you can even import your own.

For foam cutting, I’ve modified the GRBL Laser post-processor to copy the X and Y axis to U and Z. It will also move the wire to the 0,0 position for the X and U axis. This makes sure the wire comes out of the foam and doesn’t just stop and the end of the cut.

It ain’t clever

What do I mean by that? Because we are using 3 axis geometry to create tools paths and converting it to 4 axes in the post-processor we have to imagine how the hot wire will travel. Unlike a 3 axis machine which can retract its Z-axis up and out of the material, we can’t do that with a hot wire. So we need to plan our geometry knowing where the hot wire is and how it will travel. Extra sketch lines may be required that are not part of the model to bring the wire in and out of the foam.

You can see an extra 10mm line at the front of the fuselage to start the wire and end its travel on the video. Running lots of simulations with Fusion 360 and DevSim CNC foam is a must before you commit any foam.

Simulation is a must

Before you try any g-code on your foam cutter you must run the simulation in Fusion 360 and after that the free DevSim CNC Foam application. You need to ensure the wire follows the path you expect. You may need to add extra helper sketch lines to do that.

The Fusion 360 simulation will show the paths are taken by the tool(hot wire) but still thinks it’s 3 axis. Once we post the g-code then the post-processor will convert it to 4 axis. That’s why it’s important to check it with DevSim CNC Foam after the conversion.

Using the 4 axis post-processor

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Fusion 360 Post Processor for Foam Cutting 4.89 KB 913 downloads

This download contains the post-processor based on the grbl laser post-processor…

I’ve made a video series that shows how to use this. So please watch them a couple of times before you begin. Part 1 shows how to install and use the post-processor. Part 2 shows how I make a Piper L4 Grasshopper fuselage in two parts, very similar to the FliteTest Bushwacker. Part 3 shows the foam cutter making the parts.

Final Thoughts

Please use this post-processor will extreme caution. I have tested it on my machine and it works well with my simple fuselage design. You could damage your machine if you don’t run the simulations. As I have said it’s very basic and not clever but if used with these limitations in mind it could be very useful. If you are looking for something much better than this then try Dev Foam. I haven’t used Dev Foam but have used the RC airplane specific versions DevWing Foam and DevFus Foam. I have tutorials on these as well on the website.

Happy foam cutting

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