Computer-Controlled Machining
Group Assignment:
- Complete your lab's safety training.
- Test runout, alignment, fixturing, speeds, feeds, materials, and toolpaths for your machine.
Individual Assignment:
- Make (design + mill + assemble) something big (~meter-scale).
- Extra credit: Don't use fasteners or glue.
- Extra credit: Include curved surfaces.
Our CNC
The CNC in our lab is a 2008 Shopbot PRS Alpha (as old as me!). It is in its own room with the computer outside. It has a dust collector and an indexer, but that's pretty much it.
Design
I decided to make a shelf for our lab this week. It will hang above the workbench in the Shopbot room. I started by measuring the space and opening up FreeCAD. After a while, I had a large shelf, the legs, and a couple of test pieces to ensure everything fit together. I hoped to make it parametric, but like last time, it was just a headache to figure out, so I scrapped that idea. Once done, I had to export it as an SVG, but that also proved to be complicated. This week was the first time I designed something with multiple bodies in multiple planes, but I thought it would be easy to export. I assumed FreeCAD would just pick the largest side or use the camera, but that was not the case. When I exported it to an SVG, it would export just the side of the object. Despite trying again and again, it just would not work. So, I decided to Google it and found out you can use the Draft Workbench 3D object to path to make a 2D image so I could export everything, The instructions can be found here in the FreeCAD Wiki. This is something I need to keep in mind. Anyway, now onto VCarve.
VCarve
Here I used VCarve, which is CAM software. I started by importing my SVG and closed all open vectors. Next, I used the fillet tool to make all holes that were used to snap everything together into dog bones. Then, I made the toolpaths and was ready to cut.
A Little Machine Error!
Now, onto the cutting. As always, when you're in a bit of a hurry, something goes wrong! I started cutting everything on Thursday but quickly noticed an issue. Frosti and I investigated and found two problems: first, I had selected a bit that was too large in VCarve, which was easy to fix by changing the bit and recalculating the toolpaths. Second, we discovered that one side of the Shopbot was moving more than the other, the motor on the right side was misaligned. After a couple of hours, we learned how to tell the Shopbot that one side was slightly off and managed to recalibrate it. You can read how to do that here. Once everything was aligned, we were finally able to cut all the parts!
Final Thoughts
Then I sanded all the parts and it was done! Everything clicked together nicely and the joints were stiff. The only thing I would like to change is to add more function and style. However, I am still quite proud of this!
