Tag: DIY

Parametrically Designed

CNC Plasmascreen Coffeetable

Being a university affiliated FabLab has some perks: we get to pull useful items from University Surplus (one department upgrades their computer lab, other departments call dibs on the old hardware, sometimes really new stuff, sometimes really old stuff).

Nearly all of the computer equipment at CUCFabLab was pulled second-hand this way, then topped off with RAM and upgraded to SSDs. A funny assortment of other supplies end up getting collected: decades old oscilliscopes, a 1980s bandsaw, and this big old 60″ plasma screen display.

It weighs about 100 pounds and is fairly low resolution (not quite 720p if I remember right) and it took up an awful lot of table space, so it quickly got basemented. That was until my Fab Academy assignment was to ‘make something big’ and I remembered that I always wanted a coffee table that was a giant computer screen.




The neat thing about plasma screens is that a lot of the electronics are bonded to the glass (tho I can’t recall where I heard that…) and as a result, they often have a pretty thick slab of glass to start with, so it’s sturdy enough that I don’t feel nervous about setting my laptop and maybe a cup of coffee on the screen (tho a spill of the latter might be fairly disastrous if you don’t contain it before it drips into the edges…).

Putting a big slab of acrylic or glass on top of a large display is often the most expensive part of this kind of object, so avoiding that part altogether meant I just needed a cheap MDF base for the TV to sit on. Like most TVs, there’s the front body of the screen that tries to be thinner while the power supply and mainboard sits in a sort of hump on the backside. So the design of a base that goes up to this edge but leaves room for the hump turns out looking like a pool table.



It was designed using the Rhino plugin Grasshopper, which proved to be a very intuitive interface for parametric design. It is a matter of dictating the size and position of 3 rectangles (the top of the table, the base of the table, and one that can be scaled and moved as a midpoint) and then creating “lofted curves” through each set of corners. This is an automatic function that creates the whole smooth shape pictured without any work on my part. I get to just change the position of the midpoint of the curve until I like the look of the resulting curve. Then I just subtracted a box with the inner dimensions I needed from the larger shape.

After that, I have a program to do the work of planning my assembly as well. The free 123D Make by Autodesk has a great workflow to open your 3D file, type in your material parameters (“I’m using 4′ by 8′ sheets of material 1/2 inch thick”)




I got the pieces cut at the architecture lab with lots of help. I learned that with this slotted construction technique it’s necessary to drill holes at every interior corner (so in the CAD file you select each of these corners and create ‘points’ on a separate layer to export as a drill file). This was about $40 worth of MDF and took less than an hour to cut out on Architecture’s giant fancy CNC machine.

Assembling it took a lot longer. Lots of rubber malleting.



I started playing with processing sketches (like the rainbow above), but it takes up a lot of space and there’s not a good spot for it at the lab, but the TV is unvierstity property so it can’t be taken off campus, so it is hidden in a corner — the interactive processing sketches will wait for now.

Printing New Frames for Old Lenses

I think it is not an uncommon experience for people who are bit by the 3D Printing bug to look at each object in their daily life and wonder “Could I print that?” It’s also fun to look at objects and think of how you would manipulate a cube, a sphere, or a cylinder (common ‘primitive’ shapes in 3D design).

So I had been practicing Blender and noted that the lenses of my eyeglasses just pop in and out of my super-cheap plastic frames — no screws required. And of course I thought “I could print that.” It wasn’t until a newcomer to Makerspace Urbana wandered in with the same idea that I made progress.




The second design iteration

Basically, I knew how to trace the 2D oval shape of the lens (take a picture, draw a bezier curve in Inkscape on top of the photograph, import that bezier curve into Blender, convert it to a mesh, and start building the frame outward from that. But the lenses aren’t flat, and I didn’t have a clue how to measure and mimic that curvature in Blender. I wish I could remember the guy’s name (this was a couple years ago) but an optician walks into Makerspace with he same idea, except he knows about these lookup tables where you can find the curvature of particular prescriptions. It’s a pretty straight forward set of numbers: a sphere of a certain radius a certain distance from the lens. That information made it trivial to take my bezier curve in Blender deform into the actual curvature of my lens using the “ShrinkWrap” modifier. Position the curve at the right distance from the sphere, and ‘shrinkwrap’ the curve to the surface of the sphere.



Modelling the outline and curvature of my prescription lens.

The lens has a bezel top and bottom which I could measure the height of, but the angle of the bezel was just eyeballed. I simply extruded this ring outward to create the first test fit (printed at MakerLab). Plastic is now one of my favorite materials because of how forgiving it can be: it stretches and snaps and even tho I did very rough measurements, the lens snapped right into place.




From there, I printed some pince-nez style frames that I wore around for a while before sitting back down to model the earpieces in Blender. The first iteration was printed in one solid piece, face down, earpieces being build straight into the air with no supports. This worked great for a few inches, but I learned that the plastic being extruded applies a significant amount of pressure on the plastic beneath it, so that as the towering earpieces grew, they began being pushed side to side as the nozzle worked on the next layer such that subsequent layers were not stacking up straight. The night that I was determined to finish a pair (I had by now broken my manufactured frames from popping the lenses in and out so much), I wanted to be able to see on the bike ride home, so I had to finish these. Our of desperation, I braced myself against the frame of the printer and held onto the earpieces to stabilise them by hand for the last 20 minutes of the print. They still turned out looking like a dog had gnawed on the ends of the frame (the misaligned top of the print) but that sits behind my ears and I told myself it gave it a more homemade touch.

To get the lenses to fit into these frames took a few more tries (I used the same file, but the original print was done in PLA on a Makerbot, and these were now in ABS, and between the expansion and contraction of plastic and the slightly differing calibration of printers, well, point is these things aren’t always consistent.)




I got a lot of mileage out of this design, printing a few alternative colors, including glow in the dark. They looked a bit toyish, which is a style of its own. The real trick though is that they were printed with the earpieces straight up and down at a width that’s just a bit skinnier than my head: so when stretched over my face, they actually pinch just enough that they never fell off (but were still suitably comfortable.)

The next iteration (pictured at the top) was designed with hinges, but without a lot of thought into how to prevent the hinge from swinging both ways. After printing the pieces separately, I drilled a 1/32″ hole through the pivot point, stuck 20 gauge copper wire into the hole, snipped off the remainder, and filled the hole top and bottom with superglue, pivoting the hinge as it dried so that it only adhered to the top and bottom.

I liked the look of these (that PETT plastic carries light like fiber optic, so they kind of sparkle), but they did fall off my face time to time owing to the backwards bending hinges, so when I accidentally stepped on them in my morning stupor, I just went out and got contacts.