Discarded and decayed: most farms have this corner, the space where things are left. Not intentionally to rot, but a purposeless place. Things that have run their course. Mangled machinery. Broken down, perhaps with a vague notion that it will one day be repaired, but in reality, just another layer in the strata of redundancy. The wagon wheel, melting into the landscape, sits at the edge.
Ubiquity is the best disguise of all: we are blinded by it, our eyes dimmed to it’s wonder. Once these wheels were everywhere: wood and iron, bonded and bounded. The technology of agriculture and trade. And now, splintered and decayed.
The wooden wagon wheel is elegant: a device held in compression, holding an internal energy, barely caged. It’s construction, a matter of heat and sweat, temper and craft.
At the centre, the hub: an iron tube, which sheathes the axle. Iron to take the friction and heat, held in place by a simple pin. Before rivets and welding, simple wooden pegs were the mainstay of many types of fastening: clothing, timber frames, gates. Utilitarian, ubiquitous, unremembered.
The iron hub is encased in a wooden structure that needs mass: it’s the housing point for the spokes, but one that takes two types of force: compression, as all the spokes are pushed in by the rim, but also shear, the sideways force as the wheel does not always run straight.
Compression is a relatively simple force, especially for a material like wood, which is strong against this force, if applied down the grain. The mass of the hub presumably relates more to shear, especially as the spokes act as levers, amplifying the shear force from the rim to the hub. If the wheel is tightly bound, rigid, this force will presumably be distributed both around the rim, and around the hub, but any looseness and it will focus on one spoke. I suspect disintegration is both rapid, and terminal, in this case.
The hub is also our first encounter with the interface of wood and iron, and the application of bands. This leaves us to consider two factors: firstly, temperature, and, secondly, interfaces.
Temperature is the mechanism of coherence for the wheel: the wood remains as a stable temperature, but the iron bands are heated up to red, or white, heat on the charcoal of the wheelwrights forge. In an ironic twist, the heat that is needed to both smelt the iron, and to heat the band, is only possible through the use of charcoal (or other fossiliferous fuels, like coke or coal). Wood alone, in it’s primary form, will not generate the heat.
Charcoal is made by ‘burning’, although the term of the burn is a misnomer, as not all the wood is burnt by the charcoal maker: around a third is sacrificed to heat the wood around it, enclosed in an earthen or steel kiln, which allows you to control the oxygen flow. The wood which receives oxygen is sacrificial, burnt to create the heat, but the rest of the wood is effectively baked, and it’s this baking which creates charcoal. First, the water within the wood is steamed off, leading to clouds of white smoke from the kiln. But after maybe 24 or 36 hours, the smoke turns a gunmetal blue, at which point, the water, tar, and other organic compounds, have boiled out, and just the carbon remains. Now you are burning charcoal itself, and the kiln i banked, deprived of oxygen, until it’s starved to death, cooling, plinking, as it dies down.
The almost porcelain sound of cooling charcoal is not one that you forget. Charcoal is, of course, just a subset of wood, but carries several advantages: firstly, it’s much lighter to transport to the wheelwright, as all the water has gone. Secondly, it burns much hotter, maybe three times hotter, than wood itself, enabling iron to be worked in smithy and forge. As well as your BBQ.
But back to the wheel: the iron band, as heated, expands, as the energy from the charcoal is imparted to the iron, exciting the atoms, moving them apart, imbuing energy.
The red hot band is then placed, with care, onto the wooden hub, held in tongs, protected by leather gloves, and hammered down into a tight fit. But the tight fit when hot is not enough: the red hot iron is doused with cold water, causing it to spit and steam, and contract. Now, it’s already tightly hammered onto the wooden mass, so this contraction caused it to pull the central wooden mass more tightly together. It literally clasps it into place. The whole contraption held in compression.
But the technology of creation also holds the seeds of decay. Remember, our second factor: interfaces. It is typically at the interface that we find the issues: the interface between outside and in, the interface between brick and earth, the interface between wood and iron.
Each material behaves differently: iron, as we know, expands in the heat, but is reasonably stable in the damp, at least in the short term. Wood, however, has it’s own mechanism of expansion and contraction: damp. When first cut, the green wood carries a massive amount of water, but as the timber is dried, it gives much of that moisture up, distorting, shaking, as it does so. But subsequent immersion will move the wood again, causing it to warp and crack, as it differentially expands. Wood will also decay, as it’s organic compounds are consumer by multitudinous creatures. So in it’s very inception, the wheel creates the conditions of it’s own decay.
The spokes fit into this hub. They are shaped, appropriately enough, with a spokeshave, a tool that you hold in both hands, and draw towards you. Suitably sharpened, it is a decidedly satisfactory experience, the fresh wood carving almost like butter.
But why wood, and not iron, for the spokes? Wood is a tactile, and mobile, material, with a certain amount of give. In a wheel, that gives us a small amount of movement to play with. To a very small extent, wood gives a smoother ride than iron would. Plus, it’s cheaper.
With spokes in place, the outer wooden rim can be formed, held loosely in place, before the ‘tyre’ is added. Not rubber, of course, but rather another iron band. Affixed by the same technique, it’s this outer band that pulls the whole wheel firmly into it’s state of compression.
Any imperfection will be shown up at this stage, if they spokes are not aligned, the wheel can collapse from the pressure.
Interestingly, although i have described the mechanisms of manufacture in terms of solidity, and heat, compression, and shear, the wheel is, at heart, a creation of sunlight itself.
It’s sunlight that is used by the tree to grow, laying down concentric growth rings. It’s sunlight, ultimately, that is trapped in the wood, laid down as coal, burnt into charcoal, used to forge the iron, and held trapped by the wheel.
The wooden wheel was a triumph of engineering, and mainstay of agricultural technology. But nothing lasts forever. Leather did not last well, when affixed to the outer rim, but rubber was transformative, as was the subsequent invention of steel, which led to leaf spring suspension, and an altogether less bumpy form of ride. The wagon wheel became redundant.
It would, naturally, have lived on, especially in farms, where nothing is ever truly thrown away, and much use is seasonal. But in time, that inbuilt weakness, the interfaces of wood and iron, would have signalled it’s weakening, and eventual decay, at which point it was thrown to one side.
Today, of course, the same fate awaits our modern wheels: the latest DARPA efforts are for wheels that can reshape into tracks, dynamic shapes, moulding from circular, to triangular, tyres into treads, capable of tackling every terrain.
Ubiquity is no guarantee of eternity: redundancy is built into all technology. It’s hubris to imagine we are safe in any context. But it’s worth remembering the art of the wheelwright. Mastery of internal forces, art and craft. An honest technology.