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I would like to know , when welding in a patch panel. Like a rear section on quarter, how do you make the meeting of the metal, look as good on the inside of trunk, as it looks on the outside?I have done full quarter skins, and where the metal meets is way at top, so you don;t see where the two meet,( from inside trunk ) but what if you can only get patch panels!
I would like to know , when welding in a patch panel. Like a rear section on quarter, how do you make the meeting of the metal, look as good on the inside of trunk, as it looks on the outside?I have done full quarter skins, and where the metal meets is way at top, so you don;t see where the two meet,( from inside trunk ) but what if you can only get patch panels!
Filler and body work just like the outside... I wouldn’t weld And metal finish you will warp the 1/4 more than it did from doing just the outside
I do not claim to be a body man but, I do know how to glue things together....this is how I would approach
1 - trim the patch panel to size, place it on the car and trace it with a scribe.
2 - cut the existing rotted panel out while being careful to not oversize it.
3 - fit the patch panel to the car with a perfect fit or a small (1/32") gap...the gap must be even all the way around the panel.
4 - make some practice pieces of old and new sheet metal and practice welding the two together and get the welder settings dialed in....50 yr old sheet metal does not weld the same as new metal.
5 - tack the panel in making sure the fit is flush at the surface all the way around
6 - weld the panel in the panel using small tack welds and moving around to keep the heat down...stop and let cool if necessary. you can also use compressed air to cool the panel as well....be careful to not over penetrate.
7 - metal finish the outside weld. If the inside weld is over penetrated, you will need to at least knock the weld down so it is even all the way around.
8 - use a hammer and dolly to stretch just the weld, not the panel.
9 - fine tune and finish the weld on the inside as necessary.
This gives me great results without warping the panel. If you plan on using that god awful splatter paint in the trunk, I would think it would be thick enough to cover up the weld and make it very difficult to see.
Butt weld a little at a time. Just a series of spot welds skipped around to prevent distortion. Hammer and dolly after each stitch so as to bring the old and new metal in alignment and to shrink as needed. Once welded, grind the outside and make sure there are no high spots. Pick or hammer down as needed. Then go look in the trunk. Hopefully you can get a die grinder in there to remove all the visible weld bumps and pieces of wire that occurred during the outside weld. It doesn't have to be perfect, just sort of flat. Wire brush and then fill the gaps with seam sealer or bondo if you like. I usually take two pieces of masking tape on either side of the weld, then apply brushable seam sealer over the weld, followed by a smooth and thin with my finger dipped in reducer. Next, peel off the tape leaving a factory looking seam. Finish with some epoxy primer and a coat of zolatone. If you want perfect, you'll have to bondo and sand, then fill with polyester spot putty and sand, and then prime and sand.... You have to decide if it is worth the extra hassle.
Ive watched so many videos of quarter panel replacement and also read a lot of stuff on here. The quarter panel lap joint with a flange seems to be pretty popular but Ive also heard that a butt joint is the way to go. A lap joint seems to be a lot easier also? I can see how a lap joint would maybe be visible after a a while due to the thickness of metal over the seam and expansion and contraction causing cracks and also moisture getting between the metal causing rust or corrosion, I can't speak of this first hand. A butt joint seams to make the most sense but I think about the heat and then warpage concerns me.
Idealy, replacing a panel all the way back to the factory seems is the best way to go but if that is not neccessary, then lap or butt joint, that is the question?
With a little bit of body work a lap joint would be hard to see and look good for a while but the possible cracking concerns me, or do you take a chance butt welding and risk warping the whole panel? IDK
Maybe an auto body expert can chime in?
Last edited by scrappie; September 12th, 2019 at 03:44 AM.
Actually, a lap joint is very strong and stable. If done well, is not a deal breaker for me. Only use butt welding if your goal is to hide rust repair. In which case you will have to grind and weld from both sides, apply filler, etc. It's a real pain in the ***. Again, lap joints are just fine, especially if flanged to minimize filler. I did both on rear qtrs of my '80 Chevy truck and 25 years later neither was cracked or rusted. However, the butt weld was almost invisible on the back side when coated with asphalt undercoat.
If you use clecos to hold a smaller patch to the part you want to repair, if you use a dremel cutoff wheel through both panels, you will have the 1/32nd gap you want ant the patch will be correctly placed. Do part of one edge (spot welding), repeat on another edge, then finally complete cut out. Works good.
The only way to weld in patch panels and maintain appearances on both sides is to butt weld the patch, preferably with TIG. Hammer the welds flat and metal finish on both sides. Sorry, but lap welds suck The added thickness will always telegraph though the paint, especially if the car is parked in the sun. I've seen too many cars with lap welded quarter patches that look like crap after sitting out in the sun at a show. Even worse, there is no way to properly protect the metal inside the lap from rusting - weld-through primer is a joke and it WILL burn off around the weld. Your car, your call.
Lap joints do not show up (on the outside) if using depressed flanges. I have a flanging tool (vise grip with special milled jaws) that makes a depressed flange around the original body panel about the thickness of the material. You simply lay your new panel into this flanged low spot and rose weld punched holes or stitch weld around the patch perimeter. This process also relies on hammer welding to bring everything into shape. There is very little filler required and no obvious thicker panel transitions on the shiny side. Clearly, the backside will have an obvious seam, but seam sealer works just fine to prevent water ingress as proven by the many factory seam sealed joints.
I also have Clecos and have used the cut thru both panels approach. I don't use a Dremel, too flimsy. I use a Dotco with 3" cutoff wheel and this leaves a slightly wider gap that results in a lot of backside cleanup once welded.
For quickie job floor pans, I simply lap weld without flanging and seam seal both sides. Quarter repairs I either butt weld or lap weld with flange. It mostly depends on the visibility of the backside of the panel. I rarely use the cut through both panels butt weld.
Of course, this sort of work requires a wide range of metal cutting tools ranging from pneumatic Sawzall, nibbler, air chisel and shears to hand nibblers and shears. The air chisel works great for roughing out the panel quickly. Nibbler is nice for doing distortion free cut using just a 1/2" drilled hole for entry (it does require a straight edge guide if you want perfect lines). Sawzall works well for roughing out and can be fairly accurate as well, but does not work well on unsupported panels.
For hammers and dollies, skip the harbor freight junk and plunk down the cash to get a nice entry level Martin set. It makes a huge difference in the quality of the repair. Don't bother with "shrinking" hammers. These are just plain silly. To shrink stretched metal, you have to apply heat and then carefully tap to shape. You don't need to heat to cherry red, just warm it up to 300-400F (a propane torch works). Remember, metal has memory and it will flow. You just have to be gentle and not cause more damage in the process. A series of light taps is much better than one heavy blow.
Lap joints do not show up (on the outside) if using depressed flanges.
Yeah, they do, but feel free to build your car however you want. Just don't park that fender in the sun for a few hours.
In any case, I have no idea why this thread is even talking about lap joints when the OP specifically asked about joints that would look good on both sides.
Another tip for welding in repair panels is to change your MIG wire from typical ER70S-6 to ER70S-2. The -2 offers a better weld if the panel has traces of rust and other contaminants. It also grinds easier saving time and consumables.
Joe Padovano. My quarters are lap welded and I did that very early on in my career and you cant tell at all in the sun etc etc. I probably got lucky but in most cases it shows. Although I now prefer to butt weld I will disagree to an extent based off of my personal experience .A big reason why my car probably does not show is because its a much lighter color and im stingy on material and clean my welds up pretty good less is more in some cases . ON a black car you will see them every time . This is where I agree with you. Its simple thermal dynamics. You have 2 layers of metal then a thick weld covered by a much more thinner filler material. The metal holds heat so specially when it cools down the filler shrinks faster than the metal and you will see it. IN the sun the thinner metal around the weld will heat up and stretch fastert than the welded area and you will see it. So to the OP BuTT weld it. I haven't done a lap weld in almost 10 years unless its been areas where its called for ( pinch welds , trunk opneings) typical lapped areas .
September 10th, 2019, 05:15 PM
