Computer-controlled Machining

This week, we use the ShopBot to machine 2D parts for assembly into "something big". Most of the week's time was spent on training for the ShopBot and familiarizing oursevles with how to operate the machine effectively and safely. The shopbot is a powerful mill spindle that can move in three dimensions over a large bed surface area--though this week, we focus on planar cuts. Keeping with the space theme, I selected R2D2 as my subject for this week's fabrication skill, and decided to make a life-sized rendition of the beloved droid.

To begin, I used AutoDesk 123d Make to slice an R2D2 stl model into layers that could be machined on the ShopBot. The software has improved significantly from it's first release, and can generate complex interlocking scaffolding to suggest the exterior curvature of a complex shape, in addition to just slicing the model in cross-sections. The program also generates vector files (dxf) which can be imported into VCarvePro, PathWorks or other tool path software to create instructions for the ShopBot. Here's a screenshot of the interface below, where you can control material thickness, orientation of the slicing, and more:

And a close-up of the R2D2 model, with features approximated at the resolution of 2" thick slices (for a 3' total height). It needs to be BIG after all :)

Here are the dxf files to import into the ShopBot software. Some post-processing was required, as the shapes were nested too closely for the coarser ShopBot profile cuts. I also removed the numbers, as these threw errors in the VCarvePro software.

Now for the machining! Among many key steps, there are two critical aspects to setting up the shopbot task correctly:

• Generating a proper toolpath
• Selecting the proper end-mill and setting its multifarious parameters in the toolpath software

For the first, it's important to clean up the vector lines, remove extraneous lines and space the cuts with an awareness of the thickness/resolution of the tool and the types of features (i.e. notches) that you're hoping to cut. Also important to account for where your fastening screws will be (for mounting the material to the ShopBot surface), and avoid placing vector cuts near the border of your material dimensions.

For the second, the CBA shares a guide for proper tool settings by size, material, thickness, etc. It's still a good idea to check with Tom and to carefully tweak these with his supervisions and suggestions. Below is a screenshot of the custom parameters I used for a 1/4" end-mill, cutting through 2" foam.

When ready to use the ShopBot, you'll open the software, zero the tool on the designated corner of your material, and load your pre-generated toolpath. Please refer to your lab's safety training for a full set of steps for safe parameter settings and proper initiating proceedures.

Below, you can see the various stages of the ShopBot process, from blank board fastened down with screws along the edges, to the initial cut, to the growing stacks of R2D2 as I pop out the foam pieces and begin the assembly!

And the final R2D2, stacked & assembled!