final project -- weekly assignments -- about me -- fab academy
Week 13: Wildcard - CNC Plasma Cutting
We don't have that many things to test out for a wildcard... Well, not that many that are not too dangerous and offer digital workflows. So, for this assignment, I asked for, and was allowed to use the CNC plasma cutter at the Anomalous Materials Laboratory Technical Center for Thermal and Mechanical Process Engineering - A big thanks to Prof. Seabra and Daniel for not only allowing me to use their tools, but also teaching me how to do it.
The Part
For this assignment, I made the front plate for my new (emergency) final project, an electromechanical clock. Since the goal for the optics of if is to have as much tech visible as possible, a somewhat roughly finished metal part is a good front for it - I thought about doing a folding construction with a top and sides (or even a back), but... That's so closed... I could have done it, though, as it's just a bit more drawing and we have the tool to fold it. Cutting time would only have been marginally longer.
Preparations
There is not that much to prepare. The CAM software reads DXF files (version 2004 seems to be optimal), so I had to export the inventor part I had already made as a DXF. Which is, as it turns out, really easy: Open the part, right-click onto the face of it you want to export, select "export face as", and you get an export dialog:
The "Options"-button reveals a diolog to change the dxf format version, which has to be set to AutoCAD 2004 for the CAM to read.
Other preparations came down to acquiring a bit of metal foil - As I was once told at an old job, everything below 1" is foil, not sheet metal. As both Daniel and I wanted to see how cutting aluminium works (the cutter is usually used to cut steel parts), we both bought 3mm aluminium foil.
The Plasma Cutter
The Plasma Cutter is a machine built by Prof. Seabra himself, for his own company. The plasma part is bought, of course, and ia a device made for building up CNC machines from it, while all the rest is self-built.
It cuts under water, not only for being less loud and obnoxious, but mostly for safety reasons - For once, you don't want to have sparks of molten metal flying all over your workshop, and, even more important, water is an excellent UV filter, so you don't need a welder's helmet for working with it. Still, safety precautions apply, of course - Normal safety glasses are an absolute must, and you should wear appropriate clothes and shoes for handling heavy and sharp metal parts. For testing the cutting of aluminium, we used thin, disposable gloves so we were still able to feel how good the results were, but that requires being quite careful - Usually, whoever handles the material while cutting will wear thick, cut-proof rubber gloves.
CAM
The CAM process used for the cutter is a somewhat specialised software called SheetCam. It looks and feels like a computer straight from the 90s, but still seems to be under active development. It is about as intuitive to use, though, as one would expect from the looks.
The CAM process itself is pretty straight forward. First, the dxf with the part has to be imported, and moved (with a tool called "" that first has to be activated) into the right place. That, itself, is a bit strange, as the zero-point of the cutter is at the bottom right corner, and all X-coordinates are negative. If the inner and outer edges of the part are all on one layer (as they were for me...) you can now select them, put them on different layers, and see to that the inside-layer is the first one in the list. Then (first activating the "" tool), you can generate cutting tracks for both layers, again first for the inside cuts, then for outside:
The plasma cutter will make a not-so-nice hole where it first burns through the material, so the tracks automatically get to include punch-through locations outside the piece, and little arcs to meet the actual cutting tracks.
Lastly, as with most CAM processes, the postprocessor has to be run. It does all the little odds and ends to make g-code matching that special machine controller from the paths generated in CAM, and adds stuff like the safety height during fast travel.
Cutting
The plasma cutter uses Mach 3 to run, with an extra plugin to control the height of the cutting head during cutting, depending on the arc resistance. If your material is not purrfectly level and all other conditions are not absolutely stable, that is a necessary addition to get usable results.
Using it is just like with most CNC machines - You can move the machine manually if you need it to set up, you could (theoretically) even cut manually using the keyboard. It is essential to set up the Z-zero point, as it must be on the surface of your metal foil for the plasma arc to ignite. Then, you just load a file of g-code and hit "Cycle Start".
The whole cutting process is pretty quick and takes just a few minutes for the front plate.
Results
The cutting went pretty well, so there is not that much to say about the results. The edges are, of course, not super smooth, but that was to be expected - The cutter is running way to slow to make really smooth edges in aluminium, and we can't easily make it faster. For a clock that is supposed to look tech-y, that's OK, though. The bits of molten-and-rehardened metal are easy to file off, as they only stick at the very edge.
The source files are available, of course.
final project -- weekly assignments -- about me -- fab academy
