Monday, 29 April 2013

Cube X Grows Feet

Machine feet
I've been wondering for a long time how to make the corners of the cube pieces of the giant Soma cube for Nowhere. There needs to be some separation between the faces, so that they don't scrape against each other. There also needs to be some sort of protection of the corners themselves.

I have already built a small test cube for working out things like this, so I have been experimenting on that.

I found a company that sells machine feet and ball corners. The feet work well and even look okay, but at £5 for 12 I'd be looking at £200 worth of feet! Even buying in bulk from China, it looks like £100. Meanwhile, the ball corners looked surprisingly ugly, were slightly too small, and weren't really round enough to stop one cube piece damaging another.

Prototype tyre-based corner
My plan B was to cut up some used car tyres and nail them onto the corners. Yesterday I went looking for tyres. Tyre shops aren't open on Sundays, but I found a stack of moribund tyres outside one and that was enough to realise that they'd be far too big and heavy for this purpose. Then it dawned on me that I should have been thinking about bicycle tyres all along. And, what's more, Get a Grip Bicycle Workshop is open on Sundays. So I walked over there, picked up a bunch of old tyres and spent the afternoon cutting them up. The result is promising.

I can get about 40 strips out of each tyre. I'll need about 500 strips in total. But I've made a jig to help cut the strips, so it should only take 2-3 hours to cut all of them. It'd be even faster if I had some sort of shears or guillotine suitable for cutting rubber.

The strips of each corner can be glued together with rubber cement. Once fabricated, the completed corners can be left unattached where necessary, to permit disassembly and final assembly on site.

Monday, 22 April 2013

The Birth of Cube X

It's been a while (over seven weeks, in fact) since I noted that I'd proposed to build and paint a giant Soma cube for Nowhere. And the reason is: I got a grant for it! So I've been working on realising this thing.

Each piece of the full-size cube is made of three or four small cubes. The pieces need to be affordable, light enough to lift, and yet strong enough for excited people to climb on. They should also be relatively environmentally friendly, and suitable for flat packing for ease of transport. I started researching plywood.

It wasn't easy to find out which wood to use for the faces. Timber merchants sell almost exclusively to builders, who just want cheap wood at known sizes with known structural properties. So, I learned, they generally don't know how much a sheet of any given material weighs, and look at you funny down the phone line when you ask. Three different suppliers gave me three different figures for the density of the same product.

I wanted to build a prototype to see whether my choice of materials would work, before throwing time and money at building the full project. (I had meant to make two prototypes, in fact: one for each of two possible choices of wood for the faces, to see which worked better. That plan was abandoned when I learned that no timber merchant actually stocked the plywood that I suspected would be the better choice – given the lead time they quoted, I'd only be able to make a single order.) Since I'd named the pieces of the Soma cube after letters of the alphabet, the prototype would be called Cube X.

120kg of plywood, in thirds of sheets. Joy
The wood for all the faces arrived one Wednesday, at the same time as a severe migraine. Luckily I'd had the timber merchant cut the sheets into thirds to make them less cumbersome. I lugged 120kg of plywood into the building without being sick, but left it at the foot of the stairwell till I felt better. Later, Mike helped carry it all upstairs.

Each third of a sheet is enough to make six small cube faces, so the prototype would only need one of those thirds. For the frame, I picked up some off-cuts from a Brixton-based burner who answered my ad.

How to McGyver a skill saw onto a vacuum cleaner
On Saturday, I set about cutting. But first I needed something to connect the skill saw exhaust to the vacuum cleaner. Mike suggested fashioning an adapter out of an empty tonic water bottle. I didn't think it would work but, in the absence of better suggestions, gave it a go. Once we'd filed down the thread on the top, it worked amazingly well.

One prototype's worth of wood
Setting up the workbench and some templates for efficient output was interesting and time-consuming. But it won't need to be worked out again. By mid-afternoon, I'd cut all the parts I needed (and learned a lot about how to control the tools along the way).

Next, I made a template to help get screw-holes in the right places quickly and accurately. This is important because the full project needs almost 2000 screws! But other than that, I tried to cut as many corners as possible – I don't want to over-engineer the thing because time is precious, so I wanted to see how little I could get away with.

I had already guessed that it would be sensible to label the insides of all the faces to show how they go together. Doing this means the faces only need to fit together in one way (i.e. they don't need to be interchangeable) which in turn allows me to be a lot less precise about the location of screw holes.

Another thing I learned is that it'll be good to have a scheme for discreetly labeling the outsides of the pieces' faces, to indicate the order in which they should be removed when dismantling them. Arabic numerals are probably best (Roman numerals are useless – they look like accidental marks, and even if circled they look confusingly like 1 and 11). So that means I should use a different sequence to name the faces on the inside.

It probably took me 45 minutes to assemble the complete thing.

So, without further ado, here's Cube X in all its glory. It's 400mm on a side, weighs about 7kg, of which half is the faces and half is the frame. (I'll need the production frame to be a bit lighter.) It has 96 screws in it. It doesn't mind if I jump up and down on it.
Cube X
Next, I need to get hold of more wood for the frame – about 30x30mm should be right. I'll need about 100m of it! Also, I have some Cunning Plans for making bumpers to prevent the pieces from damaging each other. And meanwhile I can carry on producing the faces of all the pieces.