Attempting to box a frame for the first time, and having some issues which can hopefully be corrected. Here's the basic background. Its a 28 Chevy chassis, and its being step boxed. The frame has been sanblasted, and it is pretty pitted. Since I've never done this before, I decided to start on the center section of the frame, since its all the same height. There's about 4' between the two crossmembers I'm welding between. Welder is a Hobart Handler 140 run .030 wire, and 75/25 mix. I don't have a chassis jig, so I initially tacked in the boxing plates, moving around a lot, to avoid concentrating heat too much. Next, I started running my beads from one tack to the next, again moving around to keep from building up heat in one area. By the end of the night, I've gotten about 1/3 to 1/2 of the welding done. Two problems: 1. In one 5-6" long spot, and a couple of other smaller spots, I'm getting lots of porosity. I don't know why though. The biggest gap between the plates and the frame is about 1/16" (I cut them with an angle grinder, so they aren't perfect), I hit the frame with a 3M stripping disc to clean it up before welding. Any ideas? Is it all possible the shielding gas is getting behind the weld and causing turbulence. I'd understand if this was a problem everywhere, but its pretty isolated. 2. The frame is bowing outward a bit. On the driver's side its imperceptible, except with a straightedge. On the passenger side, its barely noticable visually, but with a 3' straight edge, against it, one end of the straight edge can be up to 1/8" off the surface. This isn't terrible yet, but I'd rather it not get worse. Since the distance between the cossmembers is 4', I assume I should have tacked a brace between the two frame rails at some point in between before I started? Any easy way to correct this, or should I continue finishing up the welds and see if it "self-corrects"? Thanks in advance for any advice.
It sounds like you are on the right track. You said "one 5-6" long spot". If you are welding that far at a stretch, that's a bit much. I try to keep it to 1 or 2 inches at a time and move several feet away, switch sides, go for a soda, you get the idea. The porosity thing is probably just the metal you are dealing with. If you haven't already, try cleaning the immeadiate weld are with a scotchbrite disc before welding. Sandblasting can leave a silica film that isn't very helpful. The wavy frame thing is probably an old issue from years of service. I did a '33 chevy chassis once that was so outta whack that I just cut it all apart and jigged it up on a chassis table. You could break it down and clamp the rails back to back if they are flat enough on the outside. I can't remember the shape. If that's not an option, strategic use of some pipe clamps (to both push and pull) could help square things up for lots of cross bracing.
Thanks - Its not bad enough to tear down - once it gets some paint on it, and a body sitting on top of it, it probably won't be noticeable. Most of my welds are 2-3", the 5-6" stretch was just two sections together that had this problem. I'll still try to shorten my welds, though. The more I think about it, the more I wonder if I didn't get something on the boxing plate in that area from carrying it around, or something. Another question - someone PM'd me and sugggested this, and also a structural welder in my neighborhood suggested this: Just stitch weld it instead of fully welding it. I know that can save it in case of crack propagation, but it seems everyone I've seen who boxes a frame fully welds it. Is either way acceptable? I wouldn't mind that underneat where its not going to be seen, but up front, I'd think it'd look best fully welded. Tim
Appearance is the only real concern. Unless you plan big frame twisting power, it doesn't matter. I don't like the stitch welded plates because I think each unwelded joint is a place to start corrosion in the long run. Not frame killing corrosion, just enough to mess with paint and such.
You might make sure your not welding near a magnet. Migs and magnets are not good friends. Also is there still moisture in the frame? WHat setting are you using for gas flow. Your 75/25 is that Argon Co2 or? Bill
Nope no magnets near it. I've got the regulator set to just a smidge north of 20 CFH, and the mix is 75% Argon / 25% CO2. Shouldn't be any moisture at all in the frame. In that case, I may leave it stitch welded, at least where the weld won't be seen, especially since I'm not a really good welder (don't have very steady hands), though I'll still grind the bad welds off and try to clean it all up. That way, if a weld does crack, it can't go the whole length of the plates. Guess I can just do a full weld up in the engine compartment area and forward. The planned engine is a 350 SBC, and the biggest power I foresee is 350-400, but even thats gonna be a ways down the line. For starters it'll be pretty much stock until I can afford to rebuild it/get new heads/etc... As for corrosion prevention, the plan right now is a good coat of Rusty Metal Primer, followed by a topcoat of Semi-gloss black. I was thinking of getting either some Waxoyl or Eastwood Heavy Duty anti rust and spraying it into the frame once all the welding and painting is done.
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