Bonnet.

January 28th, 2018

Finally had a good solid day of car stuff. I started making the bonnet.

First though a few other little things. I have a new job, a permanent one this time (bit sick of contracting and wondering if you’ll be paid and doing your own tax and so on). I am with an IT agency and they farm me out to various places. So I am now doing test automation for a big government department. This is the view from my desk.

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The big building in the foreground is the Old Government Building. It looks like stone but is actually made of wood. The Devo hat looking thing in the middle distance is of course the Beehive.

Whenever I get a new job I allow myself a present. So this time, since it is a good, well paying job, I splashed out on a TIG welder. It’s only a 200 amp unit but it will do DC and AC, which you need for welding aluminium. I’ve been practicing a little and it definitely needs more hand/eye coordination than other forms of welding.

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It is most like oxy-acetylene though. With one hand you have to hold the torch at the right angle and height and move it at the correct speed while simultaneously dabbing the end of the filler rod into the weld pool as you weld. All this is done with heavy gloves on of course. You also have to get the machine set up right – the right tungsten, ground and set correctly, the correct amperage, right AC balance, pre and post flows and so on. This welder only has a on/off trigger but it seems you can get a foot pedal for it. This allows you to control the amperage as you weld which would be very handy. Especially when on small pieces that heat up so you don’t need as much current to finish the weld.

The model I have is the home version but it takes the same accessories as a more up market, industrial one. I was able to find a circuit diagram and pin outs for that one so I can see how the pedal is wired in (it’s basically a 10K potentiometer). I have ordered a connector to fit the machine online and will do some experiments to see if it will work then I can buy or make a pedal for it.

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I definitely need more practice. So far I am just running beads. The hardest thing is getting the right amperage, the lumpy welds above were too low, and feeding in the filler rod evenly. The black marks on my test plate are where the filler hits the tungsten. You get a pop and black mess everywhere and you have to stop and regrind the tungsten again. I am not sure starting on aluminium was a great idea, it’s meant to be harder than steel to weld. I found steel was much gentler probably because the DC arc is far more stable.

The other little job I did was finally set up my stump. My log for bashing bits of metal on. I bought it with me from Auckland where, just before I moved, I had some large trees cut down. I flattened off the base (with a chisel and some fine adjustment with a coarse flap disc on the angle grinder) so it sits without wobbling and also dished the top a little. It’s good for bashing things on and also for putting the sand bag on.

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But, onto actual car stuff. I have had Joss explain the bonnet side hinge arrangement to me several times now, he’s done drawings and talked me through it and I have examined Richard’s car as well but it’s still a tricky one to get your head around. So I made a little 3D model in Fusion 360 so I could see how it works.

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The beauty of the CAD model is you can set up the actual joints and motions and manipulate the parts as if they were real. So I was able to see how the hinge works. I next made a small model test piece. I made the measurements ‘safe’, i.e. made things so I knew they would fit so the slots and so on are rather generous. On the actual bonnet I will tighten things up a bit now I know the correct measurements to use.

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One thing I am not certain of is the bend around the pin (which is 3/16 brass rod) on the upper piece. It folds over 180 degrees then wraps around the pin but the pin sits two metal thicknesses above the back of the panel. So the 180 fold isn’t quite 180 since the pin has to sit up a bit. In my test I made the first fold before the wrap around the pin a 90 degree one. I ended up levering each section up a fraction to provide the clearance. On my next one I will make the fold softer, I ground a curve onto the enge of a bar of 6mm steel I will use to hammer around. Hard to describe but you can see it in the picture and in the 3D model.

The test hinge itself works great. It moves freely but smoothly with no slack in it. It’s quite a satisfying thing to make by hand and have it work well. Basically this kind of hinge will fold completely back on itself. I did all the square folds without annealing the pieces but then annealed all the little tabs that wrap around the pin before hammering them round.

Once I knew my test would work I started on the main hinge. First I made the two top pieces. I cut them well oversize and then made the 180 degree fold for the top hinge. Not having access to a brake I did these by hand. I used my 6mm flat bar and g clamped it to a steel plate (I use that as my welding table usually) and hammered a 90 degree flange.

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Next I hammered it to 180 degrees but with a piece of 2mm steel plate under the flange to provide the slot for the hinges. I had filed the corners of the plate to provide a radius to wrap the aluminium around.

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The 2mm plate isn’t long enough obviously so I had to do this in stages, shuffling it up and down till the whole fold was done.

Then it’s just a matter of sliding the middle hinge pieces into place. Some were a little tight but a nylon hammer sorted that out. With both halves done I could rest the panels on the car and test the middle hinge. It worked great!

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Obviously the bonnet isn’t a flat panel so next job was to pull the pin out again to separate the halves then put the bend into the panels. This I did around whatever I could find. The argon bottle from the TIG was a good start then down to smaller diameter bits of tube and pipe then finally bending it over the slip roller top roller. I ran out of time before I could finish so I still have a bit more shaping to go but these are simple bends so nothing too complicated.

This is where I am at now. I think the shape is close enough to be able to start trimming a little so there is less metal to fiddle with.

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The green tape shows the approximate line the hinge will follow. The beauty of this style of hinge is there are no rivets or bolts or anything through the panel. So it should look very clean.

2 Responses to “Bonnet.”

  1. Andrew Shepherd Says:

    HI

    Spooky to think i am at the same stage as you, I am rolling my bonnet tomorrow! (sounds like an euphemism, but its not!)… and I was only thinking yesterday I need tig welder!

    Why dont you join the Austin seven specials Facebook page?
    All the chaps on there are very helpful.

    Feel free to get in touch for a chat.

    Andrew, 00 44 7979 080105
    UK

  2. Christian Soothill Says:

    Excellent stuff, keep up the good work!

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