sunken weld woes

C

cstrom72

i welded in my patch panels on the rear of my Bronco project and i have a small "gully" where the weld has sunk a little in the panel. im concerned with trying to grind it flush without thinning the metal around the weld. Ive been using a flap wheel on an electric grinder and small roloc wheels on my air grinder. I have the welds roughly smoothed down but the final smoothing seems like it would take forever going the way that im trying.. I welded in two patch panels in about 5 hours using spot welds and then splitting the distance between the welds and using a little air from the compressor to cool the welds. I would do 5 or so welds and switch sides do another 5 then let them cool for a bit then repeat and I still got more warpage than I wanted but its nothing a light coat of filler wont take care of. Im just wanting to get my metal prepped just right for my epoxy then I can use a little filler to snooth the weld areas. Any tips?? 004.jpg

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If you're going to use filler, and the level of the weld bead is below the desired finished contour of the panel, simply use a hand held sandblaster to clean the weld bead. That's the preferred method by far.
 
Hammer and dolly (on dolly) the weld. The weld shrinks and takes additional metal with it. This is why the welds are below the surrounding areas. Hammer on the welds until they are proud and grind with the weld being careful not to thin the surrounding area. Then skim with filler.
 
Another thing that will help when doing patches like that is don't trim your patch to have sharp corners-there will always be a lot of distortion in a sharp corner because the direction of the pull from shrinkage changes there. Better to cut your patch to follow the contour of the wheel opening. If you spend some time with hammer and dolly a lot of the shrinkage can be corrected but access to the backside is the limiting factor here. Without backside access to work the low areas out and stretch the weld zone you're limited to what you have-but maybe there's some pick/pry bar access-find a helper to leverage the low areas-apply pressure to the weld backside while you spoon the outside, otherwise clean it up, check for any high areas, shoot 2-3 coats of epoxy, let it set overnight, then give it some filler-more than it needs, and cut off what isn't needed. One of the biggest things that will affect warpage on a patch like that is the patch fit-gaps cause more warpage, if the butt weld is done on a tightly fitting patch it limits the amount of movement that can take place and makes shrinkage correction a lot easier because there's less warpage. I've done a lot of those wheel opening patches over the years living in road salt country.
 
So what you are saying Bob, is the more time you spend prepping fit, the better the outcome? Good info!
 
I butt welded the uprights and flanged the top (flange facing downward as not to trap moisture) The uprights of the patch turned out great no warpage but just the horizontal line at the top sunk. I tried some hammer and dolly work today with out much luck, since i flanged it its a bit to thick i think to get movement out of it. I have the horizontal weld ground down fairly well as you can see in the pics. in the morining im going to grab a couple fresh grinder flap wheels and see if I can more precicely smooth the weld out. If that wont do the trick ill see about a hand held sand blaster...
I tried hammer off dolly with firm pressure on the weld/flange its self it didnt seem to budge.. The sides i had a nice tight fit with no or a very small gap maybe 1/16 at the most but like i said i had a good turnout on the sides. If I can just get that weld out of the way I can shoot my epoxy
 
With my limited experience, I would say be careful w the flap discs bc they are very large and hard to control where the remove material. Most of the times I have had issues with thinning metal have been w flap discs. Try a 2" 36 grit or some Scotch pad type Surface finishing pads, 2" size. I think they are much easier to control. Also helps to have a partner when hammer and dolly working something like this. Good luck.
 
The 3"x 1/4" thick grinder wheels like cut-off wheels work well for knocking the tops of the welds off, grind at a lower rpm to reduce heat, a flap wheel will take off to much of the sheetmetal.
 
I really can find no reason for the flange, and have found it a lot easier to use panel clamps instead, and work with a flush fit.

Hammer ON dolly works great to stretch the weld back out and bring it back up where it belongs. I have hammered each tack as they were put down, several at a time , and the complete weld at once. The slowest and easiest way for me is do say 6 tacks, then hammer them. Do 6 more tacks, repeat.

The thickness of the flange type method makes the hammer & dolly more difficult and it can also cause ghosting problems. just one more reason I do not use that technique anymore.
 
this is where the mig sucks for welding sheet metal. it is a hard brittle weld to begin with and over stressing it makes it tend to crack. if you remove any metal other than the proud weld it will likely crack on you. take care to only remove the weld. mig welding on sheet metal needs to be done so there is very little proud weld ( bead ) .
 
Bob Hollinshead;22984 said:
The 3"x 1/4" thick grinder wheels like cut-off wheels work well for knocking the tops of the welds off, grind at a lower rpm to reduce heat, a flap wheel will take off to much of the sheetmetal.
Click to expand...

Exactly what I use to get them close and then a 60 grit sanding disc to level them being careful not to get into the surrounding material too far.
 
Lesson learned. I had heard from somewhere (not here) that a flange can add strength to the patch, maybe so but it also added warping for me. One thing that I didnt do was hammer and dolly the tack welds as I went along like Old Fart said. And like Shine says, I dont want to bang on em too hard either to avoid cracks. I made a template out of cardboard at the rear of the quarter and holding it above where my welds sunk the thickest my filler will be is about 1/8th give or take a little. More than I want but I think it will have to work. Its a non stress area so I dont think ill have any problems
 
One more thing to avoid any future problems is to seal the back side of the joint/s well to prevent anything getting in from there. Epoxy first then seam sealer should do the job.
 
Hey Bob H,

Can you point us to the 3"x 1/4" thick grinder wheels like cut-off wheels that you use. It seem like you really need a thick wheel since I sometimes will gouge the weld with a thinner cut-off wheel. Thanks.
 
Not all 4" grinding discs are designed for edge cutting. Some are designed for face cutting while others are for edge cutting then there are some that aren't good at either.

Pipe fitting ( my real world job) requires lots of grinding bevels and welds. Having used many brands and different part numbers within the same brand you can tell there is a difference in discs other than cost. There are a couple that stand out, both are referred to as *****!******(r) grinding discs. They are intended to be used on edge and face. 1/8" are common and there are 3/16" out there too.



Pferd are one of my favorite brands.
 
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