Introduction: Design a Simple Smartphone Amp in Fusion 360

About: Metalworking, woodworking, welding, homesteading - my interests are all over the map!

So, you have a CNC - maybe a Shapeoko or X-Carve, or even homebuilt. You've been learning the basics of Fusion 360. You can sketch pretty well and create simple 3D models. Maybe you've designed and made some accessories for the CNC itself like fences and hold-downs. But you want to make something that isn't for the CNC or the shop. Something someone can use. Well, here is a simple but useful and fun little project: A passive amp for a smartphone.

While it is fairly basic, you can learn some valuable lessons such as how to use parameters and constraints to make your model more flexible. Maybe allowing you to make it from some contrasting hardwoods like walnut and maple. Or make the slot bigger to accommodate your kid's giant phone. It can also be a good jumping off point because you can use the same process to design an amp with a more complex and interesting shape.

For this project, you'll need:

  • Fusion 360: This is not intended for an absolute beginner to Fusion 360. But, it isn't geared towards an expert, either. In the video I state that it is for what one might call an "advanced beginner". You have it installed and can create sketches and basic 3D models. You've done some CAM and have your CNC in a functional state.
  • A CNC router: Just about any small (or large) CNC can handle this job. You might have to increase the number of passes and take smaller cuts. Or, maybe divide the setups into 2-3 different jobs.
  • Wood: This example is made from baltic birch. You can make it from just about any decent wood though.

Know from the start that this is not a "polished" video and I am by no means a Fusion 360 expert. My intention is actually to show that you don't have to be an expert to use Fusion 360 to create models to make on your CNC. I make a few mistakes along the way and, rather than edit those out, I leave them in and show how I recovered from them. This Instructable is primarily a narrative of the video with timestamps. At my level of expertise I really don't feel I could effectively teach the design process in print alone. I have also attached .f3d, .dxf, and .stl files if you just want to make one.

Step 1: Define User Parameters

Starting approximately at 0:55 in the video, we set a handful of user parameters. These parameters are very useful in Fusion 360. Especially when used with constraints, they can help make your model more flexible.

Step 2: Design Top Piece

The top portion has the slot for the phone to sit in and runs from about 3:20 to around 9:30 in the video. In this part you'll learn to use construction lines (which I mistakenly call dimension lines a few times). You'll also see where I accidentally define the rectangle for the slot as a construction entity (which can't be used for extrusions and such). Rather than edit the mistake out, I show how I fixed it.

I also introduce a little trick that I like to use on layered assemblies like this: holes for alignment dowels. They are really easy to place accurately on the CNC and they make gluing up the layers much easier.

Step 3: Design the Bottom Piece

The bottom is fairly simple and starts around 9:35 in the video. Only alignment holes and a hole and slot for a charging cable to come up through the bottom. Of course, I start it off with a boo-boo when I create the sketch on the face of the top rather than on the X-Y plane. But again I show how to recover using a recently added capability in Fusion 360 that shows this mistake must not be all that uncommon.

Step 4: Design Center With Sound Reflector

At around 18:35 in the video I start designing the middle layer, which is the heart of the passive amp. I use a pretty arbitrary shape created using a fit-point spline. By creating construction lines in the center, I am able to do half of it and mirror it across the that line. This is a great way to create sketches more easily.

If doing this today I would have more likely used some arcs or some other entities where constraints might have been used to make the model change more gracefully if the diameter were increased.

Step 5: CAM Workspace, CNC, and Assembly

The CAM portion of the video starts at about 23:50. This example is relatively simple because the three parts are all made from the same material. A single setup is created with a fixed size box for the stock. I use cam locks (made on the CNC) to hold the workpiece, so I often "round up" the size to one that is convenient to hold without using spacers or with spacers I already have cut.

At 32:00 or so, I show the pieces being cut on my CNC. Not a lot of value there, just fun to watch! At 33:05 I show cutting the parts free of the tabs holding them and start the assembly. You can see how the alignment holes and dowels aid in putting the amp together.

So, that's it. As I said, this was not a "polished" presentation. Nor, was it intended to be an in-depth treatise on CAD/CAM. I am hoping it maybe gives some folks at that "looking for something to make" point some help and maybe provides a jumpstart to actually making things on the CNC.

CNC Contest 2020

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CNC Contest 2020