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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 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. Sadly, it is one of the least used machines in the lab.

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. FreeCAD would probably just pick the largest side or use the camera, but that is 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. This is something I need to keep in mind. Anyways, now onto VCarve.

VCarve

VCarve is an interesting software, and personally, I don't understand how it works. But that is not important for this week, so I continued. 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.

Disaster

Now, onto the cutting. I started on Thursday to cut everything, but when we started, we noticed that something was not aligned and we had selected a bit that was too large. Now, the bit problem was easy; just change it in VCarve and recompute. But the more we dug into the machine, we noticed that you could move one side of the Shopbot more than the other, and it seems the motor for the toolhead to move is unaligned, After a couple hours we learned how to tell the shopbot that one side was a little misaligned and finally where able to continue, You can read how to do that here