Introduction: Scan | Fab Table
My roommate found this redwood burl a few years ago. I've always thought it had a wonderful shape, but it was not in great condition. It has been living on the porch on top of a wood box collecting spider webs, moss, and considerable dry rot. I thought I would take the time to refurbish the burl and come up with a novel way to make some legs. I've been fascinated with the 123D Autodesk software suite and its ability to easily digitize objects for modeling and fabrication. In this case, I used 123D Catch to scan and create a 3D model of the redwood burl, Meshmixer to edit, and Rhino to produce table legs that wrap around the surface of the wood. I then cut the legs out of 1/2" plywood with a 500 watt Metabeam laser cutter.
Step 1: 123D Catch_scan
First order of business was to create a 3D model of the redwood burl using 123D Catch. There are two ways to do this, using a smartphone app or taking photos and uploading them directly online. I choose the later for this project. In order to get a good scan, it is important to have even light and take at least 20-30 photos.
Step 2: Meshmixer_edit
I exported the 3D model from 123D Catch as an .obj file. I then edited the geometry in Meshmixer to clean up and repair the model. First, I used Plane Cut to slice the ground away from the redwood burl and then deleted extraneous background geometry that was picked up in the scan. Finally, I repaired the geometry in Analysis > Inspector > Auto Repair All. This last step is especially important if you plan on 3D printing your scanned object. I choose to do this to create a scale model and see if my process would work.
Step 3: 3D Modeling_legs
I wanted to create legs for the redwood burl that would wrap around the undulating contours of its edges. To do this, I brought the 3D geometry from Meshmixer into Rhinoceros modeling software. I started with a grid to work from and began by modeling the top part of the table legs, which I used in a Boolean subtraction to get the contour of the redwood burl edge. With the dupborder command, I separated out the edges and chose the outer most one to use for my cut file. I then added the bottom of my legs, which interlock vertically for added support. I also used a "Martin" compression joint in the middle of 3 legs since they needed to be assembled from each side of the redwood burl due to the curves along its edge. As you can see, my leg design is not made for efficiency, but rather an aesthetic of abundance, resembling a caterpillar.
Step 4: Scale Model
I decided to make a scale model to test my design. I 3D printed the redwood burl at 1/6 scale with an Objet printer and laser cut legs out of plywood.
Step 5: Laser Cut Legs
I was originally planning on using a CNC to cut out the legs, but when I decided on the "Martin" joint to connect split legs in the middle, it made sense to use our Metabeam Laser Cutter, which has a 4'x4' bed and can easily go through 1/2" plywood. Cutting out all of the legs only took about 20 minutes with some additional time to test laser speed and power. The main danger here, as you can imagine, is starting a fire.
Step 6: Sanding
I started by sanding off the laser cut burns from plywood legs with an orbital sander. Then I set about sanding down the top of the redwood burl, beginning with 80 grit and working my way up to 400 grit. I was happily surprised to find a beautiful pattern of growth rings below the weathered surface.
Step 7: Finishing
To bring out the wood pattern and preserve the surface, I coated the top and sides of the redwood burl with a finish. I decided to go with a water-based oil modified satin floor finish made by ZAR. I used a sponge to coat the top surface and brush for the sides. Wood burls often get a spray finish that will create a much more even surface coating. With my hand application, some streaks from the sponge were still visible at the right angle in light.
Step 8: Assembly
With so many legs, I decided to add rubber bumpers on the bottom so that they would all sit evenly. In order to assemble the legs in the correct places on the redwood burl, I used my scale model for reference while fitting the legs into each other. The split legs with a "Martin" compression joint fit together from each side, locking in the middle.
Step 9: Done.
After being refurbished, the redwood burl now has the dignity of showing off its growth rings and standing on legs of its own.
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