This week's assignment was to make something big. The general idea being that we should do something that requires use of either the waterjet cutter or the ShopBot.

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The waterjet cutter is a computer-controlled tool that sprays an extremely high pressure jet of water at some object through which you would like to cut. The water alone has sufficient force to cut through many materials, but the machine also sends a stream of powdered garnet crystals that flows along with the water, providing an abrasive action that easily cuts through various metals, glass, marble, wood, etc. For more on that topic and the particular machine, see http://www.omax.com

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The ShopBot (http://www.shopbottools.com/) is a vertical axis CNC milling machine, much like the Roland Modela machine that we used to mill circuit boards and wax molds. The most obvious difference is that the ShopBot machine is much bigger -- capable of cutting a 4 ft by 8 ft surface (or in the configuration we have at the moment, 4 ft by 4 ft, simply due to lab space constraints).

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I used the ShopBot to cut 1/2"-thick MDF sheets into parts for two monster chairs and a table to go with them.

For the design of the chair back, I took some inspiration from creatures on one of Jace's outfits. First I did a very quick low resolution black and white drawing in Adobe Photoshop. Bringing this into Adobe Illustrator, I took advantage of a function which fits vector curves to the stairstepped raster drawing. This created a result with some nicely varying line widths with a funky look for which the sloppiness of the original drawing turned out to be a positive asset:

Though I used Photoshop and Illustrator, the Gimp and Inkscape work equally well for this task, and are free.

I was then able to export my drawing from Illustrator as a .dxf file, at which point I enlisted Heather's help to provide CAD-monkey services, and we laid out the rest of the parts in AutoCAD. For a task this simple (straight lines and fillets), pretty much any CAD program will do. Here's the set of parts required for a table and a chair:

If you wish, you can make your own monster chair using the monsterchair.dxf file.

From the .dxf file, I then had to define the toolpaths and send the instructions to the machine, which I did with the ShopBot PartWizard and controller software, respectively.

The cuts into the MDF left very furry edges which had to be sanded down. You can see them here:

Notice that I told the ShopBot to route out the monster facial features. There are four discrete levels, each .030 inches deeper than the previous. This turned out to be a little too subtle to be apparent to the casual observer, and it took a long time for the ShopBot to do the area clearance, but it helped make masking and painting really easy. Here's an extremely close-up view of the layering (looking down at the eyes and mouth) after painting: