alex_holden
Member
- Messages
- 33
I've made a bit of progress on the heater I'm building for my Morris Minor, but hit a snag too. I had some difficulty getting hold of a sheet of new steel, so I thought I'd use a set of scrap 1mm steel shelves that were fly-tipped near my office instead. In hindsight this was a mistake.
I dismantled them, carried them home on the bus, cleaned the ingrained gunge off using caustic soda and a wire brush (I suspect a local takeway dumped them because a health inspector was coming round), bashed the folded edges flat, marked out the panels, roughly cut them out using a pneumatic nibbler (unfortunately the compressor at home can only supply enough air to power it for about ten seconds every couple of minutes, but it was still easier than doing it by hand with a pair of tin snips), cleaned up the edges with a hand file, and made the folds by clamping along the fold line in the jaws of a cheap workmate clone and bashing with a mallet. At this stage of the process I was feeling quite proud of what I'd achieved so far as it's the first time I've fabricated something this complicated from sheet metal and nothing major had gone wrong yet.
This photo shows roughly how the matrix and blower will fit inside. The box is quite big compared to a standard heater, but it's a snug fit inside even so. There's going to be a frame in the bottom half that the blower mounts to with a sort of "diaphragm" on the top which seals the bottom half from the top half:
Here's a dummy build of the outer panels. There are some more holes to cut out for the water and demister pipes yet, and there'll eventually be a flap to control the front vent:
Then it was time to break out the welder. The white paint proved to be very tough plasticky stuff (presumably some kind of two-pack) that was very difficult to sand off, so I only did a narrow area where the welds were going. Unfortunately the welding proved very difficult. The weld pool didn't seem to want to form properly, and every time I fired an arc up a wide area of paint around it and on the back of the sheet burned off, and huge plumes of noxious white smoke poured off. I wound up going outside, taking a breath, coming back in, welding for a few seconds with my breath held, then going back outside to breathe and wait for the smoke to blow away. I tried a couple of times to sand more paint off around the weld area, but it didn't seem to help. I tried to use the "thin metal technique" but I couldn't get the bursts to join up and I ended up with dozens of individual tacks instead.
Tonight I decided to solve the paint problem by removing it all with chemical stripper. Once I'd done that it became obvious what the main problem had been all along - the metal is galvanized under the paint! Never having tried to weld galvanized steel before I hadn't recognised the symptoms and put the difficulty in getting a good weld and the plumes of smoke down to lack of skill and not removing sufficient paint. I added a couple more tacks and that confirmed it - even with no paint left it was still producing plumes of white smoke and leaving white sooty deposits behind. Here's a picture of the result:
I guess the only thing I can do next, other than getting hold of some non-coated steel and starting again from scratch, is to spend ages sanding the zinc off the edges where I'm going to be welding the front and top to the main body of the unit
I dismantled them, carried them home on the bus, cleaned the ingrained gunge off using caustic soda and a wire brush (I suspect a local takeway dumped them because a health inspector was coming round), bashed the folded edges flat, marked out the panels, roughly cut them out using a pneumatic nibbler (unfortunately the compressor at home can only supply enough air to power it for about ten seconds every couple of minutes, but it was still easier than doing it by hand with a pair of tin snips), cleaned up the edges with a hand file, and made the folds by clamping along the fold line in the jaws of a cheap workmate clone and bashing with a mallet. At this stage of the process I was feeling quite proud of what I'd achieved so far as it's the first time I've fabricated something this complicated from sheet metal and nothing major had gone wrong yet.
This photo shows roughly how the matrix and blower will fit inside. The box is quite big compared to a standard heater, but it's a snug fit inside even so. There's going to be a frame in the bottom half that the blower mounts to with a sort of "diaphragm" on the top which seals the bottom half from the top half:
Here's a dummy build of the outer panels. There are some more holes to cut out for the water and demister pipes yet, and there'll eventually be a flap to control the front vent:
Then it was time to break out the welder. The white paint proved to be very tough plasticky stuff (presumably some kind of two-pack) that was very difficult to sand off, so I only did a narrow area where the welds were going. Unfortunately the welding proved very difficult. The weld pool didn't seem to want to form properly, and every time I fired an arc up a wide area of paint around it and on the back of the sheet burned off, and huge plumes of noxious white smoke poured off. I wound up going outside, taking a breath, coming back in, welding for a few seconds with my breath held, then going back outside to breathe and wait for the smoke to blow away. I tried a couple of times to sand more paint off around the weld area, but it didn't seem to help. I tried to use the "thin metal technique" but I couldn't get the bursts to join up and I ended up with dozens of individual tacks instead.
Tonight I decided to solve the paint problem by removing it all with chemical stripper. Once I'd done that it became obvious what the main problem had been all along - the metal is galvanized under the paint! Never having tried to weld galvanized steel before I hadn't recognised the symptoms and put the difficulty in getting a good weld and the plumes of smoke down to lack of skill and not removing sufficient paint. I added a couple more tacks and that confirmed it - even with no paint left it was still producing plumes of white smoke and leaving white sooty deposits behind. Here's a picture of the result:
I guess the only thing I can do next, other than getting hold of some non-coated steel and starting again from scratch, is to spend ages sanding the zinc off the edges where I'm going to be welding the front and top to the main body of the unit