Hi Folks,
I am not an experienced welder by any means, so happy to receive advice on this project. Our Community Shed, (like a mens shed but we also have female members) was recently given a commercially manufactured trailer which has seen better days. It is relatively large for an unbraked trailer at 8 X 4 Feet internal dimension, all steel, but very lightly constructed. The main chassis is or more correctly was 40x40x3 angle. It had a very light checker plate floor, pretty well rusted out, and we will replace that with 30mm Macrocarpa boards, and the sides are 1.6 or maybe 2mm profiled steel, similar to that used for the sides of a flat tray ute. I have almost finished cutting out the bottom 80 mm of the sides, which were pretty rotten, but the rest of them look ok. The lateral members of the chassis were folded 1.6mm steel with a 40mm square U profile. The checker plate floor was stitched to the open end of the U shape, and these will be replaced with 40x3 mm RHS, I would have preferred a wall thickness of 2 or maybe 2.5mm, but I got what was available at the time.
Now some questions. A couple of the original U profiled lateral members, have rotted out on the ends hence their replacement with the RHS, but at least one must have trapped moisture leading to some deep corrosion of the angle, which I estimate to be near half the original thickness. Would it be OK to just lay down some beads of weld to build up the reduced thickness? Or will this lead to possible premature failure? Would pre or post heating of the area be of any benefit?
I have not measured the drawbar, but I think that it is probably 75 x 50, but not sure of the wall thickness. I note that it has been welded across the top as well as the sides where it attaches to the angle chassis frame. While I have not yet checked closely, I don't think that there is any cracking yet in this area, but short of replacing it completely, I don't see any easy fixes for that shortcoming, but some of you may have suggestions for a remedy I haven't thought of!
I have some 2mm galvanised strip to replace the section cut out from the sides, and bearing in mind my limited welding experience, (plenty of YouTube experience though) what would be your suggestions for welding that in. I have a Metalmaster 215 multiprocess TIG, stick and plasma cutting machine, and The Community Shed has a Michigan Mig welder, but I have to work under cover but outside, and although it is fairly sheltered, depending on the day it might be hard to get good gas shielding for mig or tig. I will have to get some more electrodes if I stick weld, as we only have a few old 6013s in 2.5mm I think, any suggestions for suitable rods for pretty well a novice, or at least someone with limited recent welding experience?
I will enclose some photos of the WIP Thanks in advance for your useful suggestions and advice,

Rob.
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The photo above with the corroded section of the angle out of focus unfortunately.

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This photo shows the upside down trailer frame with A frame welds shown from bottom view, and the cutout of the rotten section at the base of the sides.

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This photo shows the welded across the top of the "A" frame.

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A general view down the length of the trailer frame with one of the lateral members removed, the first one in from the tail end. The nuts welder the lateral members were used as cable guides for the brake, tail and indicator lights wiring, really rough and basic, I was surprised that the manufacturer got the compliance rating for this trailer, no jacket on the wiring between each tail light assembly and no grommets for cables passing through drilled holes in the metalwork either.
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