Originally Posted by Roadracer_Al
Agreed -- you ***really*** want to radius the edges, because the weld will crack if you just put a bead on a 90* corner.
You can easily whip up a set of T-Dollies for this job. They're designed so the stake rests on the cross-bar of your vise -- make sure that the stake is long enough so the round dolly part sticks up 3~4 inches above the vise jaws.
Use the T-Dolly to form the half-round-over on each side of the edge ( the intersection of 2 planes). Corners (intersection of 3 planes) are a bit tricky, but a little practice and you'll get the hang of it -- basically, leave the corners long, and file them back to about 45* after you've rounded the corner over.
I suggest that you fit everything first, just taping the pieces together so you can weld it all at once, preferably with back-gassing.
Also, I strongly suggest investing in some aluminum files - you'll never know how you got on without them if you do much aluminum fab. They cut fast and don't clog. You'll like'em, I promise.
Regarding your bends, make sure that you use a generous radius -- aluminum doesn't like to be bent sharp or crisp -- it will break along a sharp bend. The minimum recommneded radius depends on the thickness of the material, but a wider radius is always better b/c it won't crack as easily. Again, you have to build your corners carefully -- they'll be the meeting of 3 radiused edges.
I looked up T dollies and found a youtube video of some guy doing this. looks cool. What's the difference though when you join the parts together? It's still a butt joint or am I missing something? I can make one of those dollies easy enough and the actual forming doesn't look difficult at all.
My other issue is that I have designed this part to fit fairly snugly in the hole and the wildcard of making those radius corners as that I'd have to redesign it and not really know how the bends would turn out.
I've been bending 90 degree sharp corners on 5052 aluminum and it comes out great. I made my second set of panniers this way and the bends worked great no issues with doing it that way.
I have some aluminum files and they do make a big difference. Cut aggressively and leave a razor sharp edge
I'm going to make up a prototype from aluminum today and see if I can get it to work. I'll offer it up for critique and you guys can mark it up and tell me where I should be radius-ing corners.