Thanks, not much to show but once I have a story to tell I will update the build. Lots of parts started, nothing done. But lots of fun.
Thanks Beans

The key to welding sheet metal is to get good penetration.
You can practice on some scrap metal. Go and get some strips from somewhere before you attempt this.
You will have good penetration when there are walnuts bleeding thru the back side.
You can then grind the proud and walnuts off without worry of the metal cracking as the whole thickness has melted together.

For butt welds, get the fit tight with no gaps. It's crucial for the two pieces to be flush before you tack them together. If they are not, grind the proud off your tacks and carefully tap with a hammer on dolly to get them flush before welding.


Be careful, penetration is good, but too much means you've over heated it and will warp the panels from the shrinkage that occurs when it cools off.

For butt welds, you can get the warp out with hammer on dolly on the welds after you've ground off the proud. You may be tempted to strike somewhere other than the weld because there is a hump off to the side but don't do it.

One final thing.............practice!
Do some corner welds, T welds, and butt welds.

OP: What welding method do you have?

Marten wrote:

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I have a small mig welder. Hobart 140 is the model.

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 That inside corner is not something you can MIG all the way up. Polishing out the lumps would be a pain.

It would probably warp the bed side as well, beyond repair.

Are the stake pockets attached yet? You could attach an L angle inside and then plug weld from inside the box.

 

Just make sure that the sheets are dead flush before pulling the trigger to tack.

MIG welds are more brittle than TIG or gas so you don't want to knock them too much.

Skip around and blast a couple of tacks in one spot at a time.

It will help from it getting too hot. The cooling off process is what causes distortion, so the less it gets hot, the less distortion.

Oh yeah, do some practice bits....or did I say that already?

Marten wrote:

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Thanks guys, I will try this out and see what happens. Pugsy, for the stake pockets I was thinking of tacking them on and then caulking them with seam sealer. Hopefully keeping the tacks small enough to be covered.

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 Use some kind of plastic tool with a 45° notch to spread a nice line. (You could use the wife's credit card for this.)

Make sure the notch is higher than the biggest tack.

Hey Marten, we've spoke about your box.  What you've done so far looks really great.   You are going to have such a great time with that truck when you're done, cuz you did yourself.  Good on you and keep it up...

 

Interesting look at stitch welds.  Worth a watch,  

 

And like every one else has already stated,  practice practice practice...