Sunday, March 28, 2010

Wagon forecarriage

My son has just called me a twat. He was practising Dvorak's Humoresque; I felt moved to accompany him as if it were funeral march. After five bars of this he looked scathingly at me for a silent moment and declared
'God you're a twat,'
and I felt very proud of how discerning he has become.

Because I am.

Anyone else would have designed the pivot of a wagon in an instant; it took me days and days to think of a head tube. Which, eventually, I did because it admits of a full lock, and your first wagon, which has a feeble half lock, soon teaches you that the front wheels need to be able to turn right round and point backwards if the thing's going to be used in the garden. And that leads to another design concern: maximum body height is 20 inches or the thing will topple over from time to time when a female person of the opposite sex treats it like a mobile compost heap, which I strongly suspect will happen since she bloody well never empties the cart, the hateful witch. - Not that I would ever criticise my wife, other than here in this obscure little corner of the Internet which I happen to know she doesn't visit - Given that this is a monocoque and that one axle needs suspension so that irregularities of the ground don't result in an occasional aerial wheel, this dictates 16 inch front wheels and in turn this necessitates nicking them off my bike trailer because those ones are already sprung.

I use car valve springs because they're free: your New Zealand Councillor has decided that recycling a car shall cost you fifty dollars, and the result, predictable to everyone bar politicians, is an endless supply of donor vehicles up the Old Coach Road. (Or was. Until they clear-felled it, when dumping became rather more risky.)

Car valve springs bounce up and down rather excitably so you have to tame them by lashing several under compression with big zip ties. We dignify this makeshift by calling it 'pre-load' so that wives-and-daughters think we know what we're talking about. In theory the bouncy bit needs a firm attachment to the not-bouncy-bit. In practice notched tubes work though I do weld tiny internal stubs to the dead axle, around which the bottom springs are jammed solid.

For this wagon the bike trailer's four springs were augmented with two more, making three for each wheel, piled on top of one another and tightened down with my zip ties.

Basic welding turns a head tube into a rotating tripod, the verticality (is there such a word?) being determined by using a kitchen cupboard door as a welding jig, bolting the supports to it before welding. Yes of course there's some distortion. That's what hammers were invented for. Anyway how accurate d'you want the steering to be for goodness' sake? It's only a hand wagon. And before my son affords me any more schoolyard commentary, the cupboard door was pre-chucked-out. My family are astonishingly stupid, admittedly, but not stupid enough not to note a sudden surfeit of drilled holes and welding scorch marks on the kitchen furniture.


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