There’s something about light shades. I see them as an opportunity to introduce a sculptural element into home décor while still being functional. (Being an engineer, I disagree somewhat with the famous William Morris quotation: I prefer to fill my house with things that are both useful and beautiful.) And the fact that illumination is involved makes it all the better, somehow.
This time a couple of years ago I was working on a light shade design for the pendant fitting at the top of our staircase and learning how to use the CAD/CAM software Fusion 360 in the process. The end result was this shade based on a 60-sided polyhedron, and it continues to make me happy whenever I see it lit up. Should you wish to make an identical one, or just something like it, all is explained in my Instructable, Polyhedron Light Shade.
There’s a second pendant light on our landing and, I’m ashamed to say, it still has the same shade that the previous owners left behind in 1986.
It’s made of a woven cane and very dated. I don’t much like it, but we’ve never got around to changing it.
I’ve been working on a replacement. I could have just made another of the polyhedron ones, but where’s the fun in that? And this light is round the corner from the top of the stairs so you can’t see them both at once. I felt that something less tall than a 38cm globe was sensible, given that it doesn’t have the ceiling height of a top-of-the-stairs light.
I started playing around with torus (doughnut) shapes and discovered that, hidden within every ring torus are oblique circles called Villarceau circles (after the mathematician of the same name) in addition to the move obvious circles that define the cross section of the torus and its overall diameter. It’s explained very neatly in Wikipedia’s Villarceau Circles article. This discovery opened up the possibility of creating a torus shape in a more interesting way than simply cutting a bunch of cross section circles and arranging them in a ring of the right diameter.
I squashed my doughnut to stop it from being too tall, which makes my Villarceau circles into ovals. I used the design software to explore how to form a torus from the crescents created by overlapping Villarceau ovals, and how many such crescents would best give enough bulb coverage to prevent glare while still allowing plenty of light to escape. The first attempt, rendered using Fusion 360, I reckoned was too squashed.
I settled on a more moderate degree of squashing with 5 crescents sloping to the right and 5 to the left. Each one intersects with 5 of the other variety, at 3 different angles, which means the slots by which they fit together have to vary in thickness from a narrow one in the middle to the widest ones near the tips.
Well, it’s all very well designing something but sooner or later you have to find out whether it’s actually buildable. Having modelled it to suit the 1.5mm thick plywood I want to build it from eventually, I then re-sized the slots to suit some thicker corrugated cardboard I retrieved from a large wheelie bin outside a convenience store.
Corrugated cardboard isn’t an ideal material for laser cutting, it can catch fire very readily and the burning isn’t obvious if it’s within the layers. I watched it like a hawk with one finger on the pause button and a damp cloth in the other hand, which I did need to deploy a couple of times. The end result was that several of the 10 crescents were slightly charred in places, but good enough to use.
Assembly was a nightmare, especially by the time I’d got 7 or 8 of the crescents slotted into place. I’d taken the precaution of orienting the corrugations to give a little flexibility in the tip-to-tip direction where it’s most needed when trying to interlock each crescent with its 5 neighbours. I don’t think you could build this from a completely stiff sheet material. Fortunately, my plywood is also slightly bendy in one direction.
This does seem to have worked and, holding it up near the existing light, it looks to be a suitable size and shape.
I still need to decide how best to suspend the shade from a pendant fitting but I have the confidence to go ahead and cut the real thing from plywood now.
It should look something like this rendered image when I do.
YorkshireCrafter 