A Special Builder's Notes


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01 March 2013

Last Time I Looked...

... I'm sure it said that phosphor-bronze filler rods were just the ticket for TIG brazing. Anyway, when the rods arrived I thought I'd get re-acquainted with the process and revisited a couple of welding forums. I was concerned to read that most people seemed to have problems with the phosphor-bronze filler and certainly wouldn't use it on mild steel - except one chap, who wouldn't use anything else and it was the answer to most of his prayers. I was beginning to envisage further delays whilst the rods were returned and I undertook further research but in the end I went with the chap who'd got the results and gave it a go.

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As far as I'm concerned it did everything I wanted it to do. I'm a beginner when it comes to welding but I could see immediately that this process in the hands of an expert would produce superb results. I imagined that the braze would, like in gas-welding, flow around the joint, but it doesn't - well, maybe it's meant to but it didn't for me. It looks exactly like a TIG weld but with a bronze finish. With a flame the heat would be distributed more widely and make it easier for the filler to flow perhaps? The TIG torch produces a much more localised heat so the filler moves very little. That's actually the tricky bit; depending on the thickness of the metal and the surface area adjacent to the braze, the amps must be adjusted so that 1. there's not enough heat for the parent metal to form a weld pool but just enough for it to fuse with the filler as the rod melts and 2. that the heat doesn't dissipate before the filler has melted and formed the fillet. So there's quite a lot going on in a very short space of time and plenty of scope for disaster. Half an hour on some practice pieces got me into the swing of things and established that between 22 and 35 amps was my range. I should really have attached the pedal control but I find that rather awkward for the small amounts of TIG that I do. Of course, the other thing about TIG is that if you're not sitting or leaning or otherwise comfortably supported, don't even begin.

And here's the first of the friction dampers...

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I've just got to bore the centres for the bronze bush....

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...squeeze in the rubber inserts and drill a couple of holes in the chassis for the mounting bolts. By the time they're powder-coated, I think they'll look every bit the part - I must say I'm very pleased with the way they've turned out and the TIG brazing process is going to be extremely useful in the future. In fact, as soon as I'd finished the dampers, I got straight on with the brake pedal and shaft brazing so that's all ready to go back in the car over the weekend and I can measure up for the extra bellcrank that will operate the front brakes' master cylinder.

The other excitement this week was the collection of the ash for the body frame and Douglas Fir for the floorboards - courtesy of The Great Collector. In another aborted career, I used to build what I called a 'Merchant's Chest'. It was a 24 drawer piece of furniture that was going to take the world by storm - how could anyone live without one?

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With ease, it transpired. But the point of this digression is that I made these chests entirely from reclaimed Victorian factory floor joists - Douglas Fir. There wasn't a knot to be seen anywhere in the planks; the grain was straight and it had a warm, pinkish hue. It was also incredibly hard-wearing though apt to splinter if too dry. The French light aircraft manufacturers, 'Jodel' (I had one of those) made use of Douglas Fir in their main spars, so it must be good stuff. Anyway, that's what the floorboards will be made from; I knew you'd be interested.

And, as if that wasn't enough for one week, yet more excitement came with the arrival of the stainless steel mesh...

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It's the same as the stuff on all the racy Astons and Bentleys, last time I looked.

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