Make a Speakerboxxx
Having long since become the norm in industry, digital fabrication is now a standard practice across much design education. This How To walks you through the basic steps of the digital fabrication process using a CNC 3-Axis milling machine, from design conception to digital modeling, toolpath design, and milling of a simple object: an iPhone speaker. Although the process may be effectively scaled up in many ways, this How To will give you a grounded understanding of the digi-fab workflow. Get ready to cut!
Step 1. Build a Digital Model
Although this video shows a process for making model in SketchUp, this process may be accomplished in a variety of programs, such as Rhinoceros 3D or a variety of Autodesk Products. Regardless of digital modeling platform, Henry outlines a few general suggestions for constructing models for CNC milling:
Make copies of parts before making new changes so it’s easy to revert back.
Work at full scale. Milling a site model base? Shrink the model.
Build the speaker in halves: top & bottom. This allows you to machine the “funnel” that directs the sound down into the speaker dish. This dish projects the sound outward:
Step 2. Create Toolpaths
Many software applications exist that translate geometrical data into actionable movements for a CNC router. At the Boston Architectural College the router uses Vectric software (Cut 3d). Critical settings include the bit size and shape, material size and other properties, and paths of the bit through the material. In this video Henry explains what the various settings mean while setting up the Speakerbox file for milling.
While using Vectric software (Cut 3d) the software consistently wanted to machine the outer perimeter of the piece, despite my best efforts to “tell” it not to do this. As a result, the machine time was three times as longer than necessary.
Step 3. Set Up Machine
After spending so much time at the computer, it’s time to stand up and affix your material to the milling machine’s spoil board. Listen closely to Henry’s explanation of this critical (if a bit messy) element:
When preparing to machine the speaker, secure the “blank” from which the speaker is to be machined to the table with industrial grade double-sided tape. This is the best way I have found to hold the parts in place once they have been cut free from the blank. DO NOT SKIMP HERE! Use a high grade commercial carpet tape. Make sure to cover the entire back of the blank evenly, and that the spoil board is dust free. If this tape fails… I don’t even want to think about it.
For example, when the sound hole in the top half is machined, it is done so as a sculpted contour, not a pocket. This means that the center disc is free once the cut is complete. Tabs are challenging here because the contour is curved (it is the top half of a hemisphere).* A screw in the center is challenging because the bit surfaces the entire top before beginning its cutting paths and if it hits a screw you’ll be buying lots of new bits. If I were going into production with this little honey, I would design a vacuum fixture specifically for this design, but that presents its own challenges.
*As far as I can tell Cut 3d software does not allow you to put tabs on 3-D surfaces. This makes sense in that it would be difficult to easily “clean off” the tab once the part was completed.
Step 4. Run the Job
Typically a minimum of two passes are required to create a smooth surface. In this demo we only performed one pass for sake of time.
I have found that for the cleanest possible resolution / surface of the final product, you should use a small diameter ball nose or radius bit. In addition, originally I had the machine make multiple passes in different directions: 1 pass in the X direction, one in the Y, one at 45 degrees to both the previous passes, then one at 135 degrees to all the previous. However, this means your total machine time is well over an hour for this little thing. So, to speed things up, you can play with the step-over and jog speeds, but at the end of the day, we just went with one pass and some added hand finishing.
Step 5. Remove, Extract, Finish
Often, parts will remain attached to the material after milling so as to not let small pieces fly around. In that case you’ll have to remove the part from the excess material, which may require only a knife, or power tools depending on the material and remaining material. Afterwards, spend some time with various grades of sandpaper if the milled surface textures aren’t to your liking.
As stated above, we hand-finished our speaker parts and then glued the halves together. At one point I was toying with the idea of machining my own spherical sanding ball that I would put on a spindle and chuck up in my drill press. This would allow me to sand out the hemisphere perfectly every time. Again, if I were going into production with this, that’s probably what I would do.