Introduction: A Third Leg — 4-Axis CNC Milled Limb

Picture of A Third Leg — 4-Axis CNC Milled Limb

In the process of fabricating a wooden leg as component for a recent art installation entitled Street Feet (2017), I navigated a variety of technological and practical issues. These issues were the result of both machine and human limitations that challenged my problem-solving abilities and made me question my overall intentions to make such an object for the sake of absurd and comedic rhetoric.

Street Feet was a satirical shoe store/ contemporary cobbling shop located within the Visual Art Center exhibition space in Austin, Texas. The meat of the conversation being conducted was a jab at contemporary trends in revivalism that appropriates and exploits past traditions and cultures. This leg was a strange, uncanny prop of the cobbler's workshop, intended to convey a deeper sense of disturbed discomfort.

Let's get into the process...

Step 1: 3D Scanning

Picture of 3D Scanning

Capturing an accurate model of my foot was one of the most challenging aspects of the process, almost purely due to my lack of ability to hold my toes still for the length of time required to replicate the full limb. I used a GO!SCAN hand-held 3D scanner in a dark room (with the help of a friend) to capture the model. In order to depict a clean set of toes, I ended up having to patch together a few scans into a single foot using the 3D scan editor Geomagic. A few hours of tweaking and polishing across a number of 3D editing applications resulted in a nearly-realistic scan of the foot. The milling machine couldn't capture the truly exact details, so some wiggle-room of accuracy was allowed.

Step 2: Milling Prep

Picture of Milling Prep

The next step was to adjust the model for fabrication based on the specs of the milling machine. The Roland MDX-540A 4-axis mill could not render the full form of my leg and foot in a single piece, so the limb had to be separated into two pieces for manufacturing.

After using Rhinoceros 3D to sever the foot from my already-severed leg, I added the proper armature require for secure and safe milling. Additionally I alined a peg and hole system that would allow me to adhere the two piece after fabrication.

Next came a trip to Austin's Fine Lumber warehouse to select a hard piece of poplar to laminate into the proper block needed for the full form of the leg.

When I had my materials ready to go, it was time to get the mill up and running. This was my first 3D milling experience, and I was not yet fully aware of the limitations of this machine. I quickly learned that the girth of my meaty calf was larger than the maximum diameter of the mill. As a result, I was forced to scale the model by 10%. I was disappointed to have to alter my project for no excuse other than the machine limitations, but this smaller size proved to be more useful in the end. The foot needed to be a holder for a variety of shoe sizes, and my size 13 foot reduced the capabilities of this prop.

Step 3: Milling and Assembly

Picture of Milling and Assembly

Next, it was time for fabrication. The milling of the two pieces took almost 20 hours, including 2 roughing passes and 2 finishing passes for each, with progressively smaller bits. The armature required for milling left me with some clean-up to do by hand, which practically doubled the total time for fabrication. After polishing each piece, I alined, clamped, and glued the two pieces into the full leg.

Step 4: Finishing and Presentation

Picture of Finishing and Presentation

As a finishing touch to the leg, I decided to create a faux-vintage look to accentuate the nature of its presence within a revivalist cobbling shop. I applied a white pickling finish to the wood, and then sanded and worked the surface to replicate some wear-and-tear and bring back the gorgeous grain of the poplar.

Next, it was time for the exhibition opening! The leg sat propped in a bench vise on my shop table as I performed in the space as a worker and attendant to the retail store. Though none of the items were actually for sale, the nature of the entire installation left people in an uncomfortable space of uncertainty—a limbo state where I think an audience is most susceptible to contemplating new ideas. The project collectively drew some intriguing criticism and conversation, and has sparked the current path of my work.

Check out the full multimedia project here!

Comments

tytower (author)2017-07-22

Hey ! That looks like my leg that I lost . What are you Dr Frankestine or something ? Send it back.

Swansong (author)2017-07-22

You got a surprising amount of detail into the leg. :) I hope the exhibition went well!

About This Instructable

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Bio: Hello! My name is Henry, I'm an artist and designer from Chicago. I currently live and work in Austin, TX after receiving a fine ... More »
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