remove all the old panel except a few inches of overlap.
Fit the new panel, test fitting door, trunk lid, tail ext. etc.
scribe old panel using the top of the new panel as a guide.
Remove new panel and cut old panel at bottom of the scribe line.
This theoretically gives you a tight butt joint, but you never can cut it that accurate.
refit new panel, marks any areas of joint that are tight, lift up new panel an inch or so so you can grind the edge a little until you get the butt joint with the space you want.

 

here's how I did it. These are butt welds. Cut off the old panel but leave plenty of metal so you have a bunch of overlap. Line up the new skin and get it where you want it. Hold it in place to the overlap of the existing quarter with some sheet metal screws. Use a cutoff wheel to cut through both panels at once starting in the middle of the quarter and working outwards. Drop a tack weld every so often to hold the skin and the remaining quarter together. If you want, cut away the scrap on the new skin every so often to get it out of the way. The scrap on the existing quarter will be tougher since it's behind but you can reach it with a small cutoff or a Dremel. By the time you get all the way from from front to back and down the front edge you'll have the skin held on by tack welds and once the scrap is all cut away you can fill in in between the tack welds. Use plug welds on the wheel lip, trunk dropoff, and taillight filler panel.

 

Nice job Andy

 

Mike's method works really well.

 

I like to over lap the panels and use a few screws to hold them together then I use an air powered hack saw to establish my seam. cut a few inches at a time, remove the excess add a tack weld and keep cutting. the saw blade is really thin and makes for a really thin weld.

 

Sheet metal can be a tricky thing to work with. You will need some gap between the panels (about .035"-.040") because a tack weld on sheet metal will suck both pieces together very quickly. If the pieces are too close together when you start you will end up with them wanting to try and overlap themselves and buckle. Once you get your tack welds all within a couple inches of each other you should be fine after that.

I used a pretty thin cutoff wheel. Had a nice narrow gap when done, narrower than I would get with those panel clamps. I had some warpage but was able to get most of it out by working the welds over with a hammer and dolly.

 

Sheet metal can be a tricky thing to work with. You will need some gap between the panels (about .035"-.040") because a tack weld on sheet metal will suck both pieces together very quickly. If the pieces are too close together when you start you will end up with them wanting to try and overlap themselves and buckle. Once you get your tack welds all within a couple inches of each other you should be fine after that.

 

And what happens to the surrounding metal when the panels are sucked together? It warps. That's why people who know how to butt weld with full penetration do so with zero gap. Or at the very worst no wider than the wire being used, which is .023 for most body panel applications. .040 gap is too large, just like those gimmick panel clamps provide. I've posted photos of a Mustang quarter I did with zero gap, which is how I weld all my patches and panels. Here's another "hack" who welds with zero gap: http://metalmeet.com/forum/showthread.php?t=798&page=2 Search any master car builder and you'll see panels joined in a similar fashion. No gap. And no, I did not make entire cars from scratch. You rarely see that type of work on hobby forums like this.

 

I had good luck welding in a patch panel using no gap. This was my first time attempting this. I kept the panels flush where needed with a hammer handle while tacking the panel in. I ended up with a tack about every 4" or so. To finish up, I welded about 1/2-3/4" at a time jumping from one end to the middle to the other end and cooled the welds down with an air hose as I went. I ended up with very little warpage from welding.

Grinding down the weld was another story. Grinding generates a lot of heat. Luckily I made the joint close to a body contour line where the metal is stronger.

Good luck with whichever method you choose.

Sent from AutoGuide.com App

 

And don't forget,grinding (too much) will also weaken the seam.

 

You will get the best results if you seek up on the trim mark, you don't want to try it nail it the first go around. You will also get the best results if you use tin snips to make the final cuts.

Another benefit of the tin snips, as told by a sheet metal master, is that the snips stretch the metal out on the cut line. As you weld the metal shrinks, by having the metal pre-stretched, although a tiny bit, the distortion is less.

Never understood the buttweld clamps that Eastwoods sell, and yes I have some. More often then not, the gap left by those clamps .040, is wider then the thickness of the metal you are welding. Companies like Eastwoods spread this notion that you NEED a gap when welding sheet metal then creates the solution, a product that produces the PERFECT GAP.
F*ck what a load of crap.

These clamps create more work, a gap of .040 is far harder to weld shut then a no gap joint.

If you are covering your weld joint with filler then you have distortion. Sorry but you CAN NOT weld and NOT get distortion. Several things effect distortion. Gap, heat exposure and cooling rate. If you are welding with a MIG, then you have no control over two of the three, you only have control of one and that is gap. The less gap you have the less distortion you get.

A few tricks can be made to make those clamps better. Trick one, swap out .040 piece of metal for a thinner one. I've seen a few done with metal banding material, and some with razor blades! Trick two, mark out the location you plan on installing the clamps and make a notch on one of the pieces of metal wide enough for the clamp. The notch recesses the clamps.
Now when you hang your panels you have a no gap to little gap across the entire seem, the only gap you would have to weld is the notches you made.

If someone wants to change their method or not change or commit suicide, frankly I don't care. Just trying to post factual information and not some crappy Eastwood propaganda. The time spent getting a no gap to little gap is not that much more time, but saves time during welding and post welding prep...Eric

 

I also use tin snips as my final cut, a great way to get a tight final cut with no added distortion. Never close your snips all the way, you'll leave a "twist"" in the metal, just use the back half of the jaws, never the tip. I use Wiss greens/reds "straight" snips, not offset, they give you the best control. Welding with a light-activated helmet will also give you the best results and limit distortion. I used to weld without a helmet and just point/pull for the tac but a large patch will do you harm. Misguided welds will do nothing but add heat where you don't want it and seeing your target is key!!