Panel adhesives, in this case I speak of 3M 8115, have glass "*****" embedded in the adhesive that "hold a gap" when the panels are clamped. This is done to ensure that the adhesive is not squished out and that the appropriate amount of adhesive remains in the joint. That said, the best way to clamp the panels is to use whatever clamps fit the panel. Here is a photo of the firewall I installed in a 56 cab...vise grips were used around the perimeter to hold the panel in place while the adhesive cured. On other "blind" panels I have used Clecos and sheet metal screws with good results.
If you have the opportunity, check out Kevin Tetz' video in the Paintuacation series on panel replacement...he replaces the rear quarters on a Mustang, one side with welds and the other with structural adhesive. This is a good comparison video from a master body/paint man.


There is another photo of a dash repair panel that I installed over the original dash...would anyone REALLY prefer to weld on this dash? As an added note on clamping, do not over-do it, you can cause dimples and distortions in the panel. The adhesive does the work, all you need to do is hold the panel in place for 90 minutes until the adhesive sets.

 

Most of what I do is butt welded. I took a course in auto body at a local vo-tech school back in the 70s and my first 2 weeks were spent gas welding butt joints.

My last lower door repair was on my 55. After fitting the repair panel, I used butt welding clamps to hold the panels in alignment. Since the clamps leave a small gap I back up my welds with a copper fixture to help eliminate blow thru.



I tack the panel, remove the clamps and start welding the panel with small short welds, moving around to prevent heat buildup. I usually take a small grinding wheel on my die grinder and dress down my welds to where they are just proud of the surrounding panel. I don't like to use a big grinding disk on welds because of the chance of thinning the metal and excessive heat buildup around the welded area.



Back side of the panel.



And nearly finished.






As far as the ghost lines, I guess there are a lot of opinions about why they show up in some panels. I usually notice them on dark colors after they have been in the hot sun for some time. Most popular opinion that I've heard is that mig welds are very hard compared to tig or gas welds and therefore they expand different to the surrounding metal and create the ghost line. True or not.....up to you to develop your own opinion.

 

So I guess you guys don't bother dressing down the back side of the welds?

One thing I learned on the Butt-Weld Clamps....I mark them, and grind them a bit wider so the panels fit flush except for the clamp areas.

 

Chuck, I am not sure how to get clamps on the outer door skin with the inner structure in the way.

Clecos perhaps, or maybe some pop rivets temporarily?

 

A lot of things are done in commercial body shops and assembly lines because they are easier and faster, and/or take less skill. They don't care what happens later, they will never have to look at it again, only how much profit can be made. I am an advocate of butt welding repair patches (see my rust repair tutorial) Every sheet metal weld, no matter how it's done will shrink. A flange or overlap weld will not be able to be stretched back into shape as already mentioned and you'll have the doubled metal wrapping the edge to do ??? with.
Adhesives are great, most of my Solstice is glued together, most commercial airliners are glued together, but the manufacturers would not glue a lap joint in the middle of a panel unless they were going to cover it with trim. I don't understand the problem with metal finishing the inside of the door skin, just a matter of using the right tools. The doors have a large access hole to work thru, and I would not hesitate to cut more of the inside panel out and put it back after finishing the outside if need be, you are likely going to be covering the inside with an upholstered panel anyways so metal finishing it would not be as big a concern. I find that the biggest problem with bodywork is the "instant gratification syndrome", many are in too much a hurry to get it done rather than take a little longer to do it right. If you do it right the first time, you can be proud of it for a long time. Rush thru it and you'll spend a lot more time apologizing for it.

 

Thanks Ax.

The thought of cutting the interior panel back for access had not occurred to me. While more work, that is definitely the only way I have had anyone mention on how to access that area.

 

I use the butt weld method using the same method and clamps as Drew. I will finish both sides of the metal pc if easily accessible. As in the case of the doors I would verify no holes in my welds, if not than I would coat the inside with a rust preventive paint,I use KBS Coatings - Gas Tank Sealer - Rust Prevention - Stop Rust Paint - Clear Coat Paints I than would apply the sound deadener material and no one is the wiser if I don't tell them. How would you finish the inside of the interior panel once you welded the panel back together after removing to access the ouside skin inside welds.

 

You wouldn't....

Like Ax said the interiors are typically covered, and ghostlines on the interior do not concerne me near as much.

 

Note that the 56 door has a vertical reinforcing post for the hinges inside the front of the door, so you will not be able to access the frontmost 4 or so inches of the back side of the panel to grind the weld bead smooth, but that is not a major issue for that short a distance or you could still slip a spoon dolly between the post and the doorskin if you need to stretch it. Just get plenty of practice, experiment with the settings on your machine, and have a tight butt joint so you don't end up with a lot of steel "snots" on the back side and you should be OK. If you are planning on stretching, metal finishing the seam, be sure to use the 0.025 ESAB Spoolarc Easy Grind wire only. The common MIG wires with 4 digit alloy # designations are way too hard and brittle to hammer stretch successfully. Also CAREFULLY fit the seam so that there are no gaps wider than the wire diameter!!! I am not fond of those panel clamps because of having to deal with the gaps they make. If you must use them, I like the villains suggestion of marking and filing just enough space in the seam for the panel clamps while making the rest of the seam tight. HINT:If you should have a wider gap and can't adjust it, In addition to using a copper backer I save a length of the 0.030 Easy Grind wire, and lay a piece of it on top of or into the gap as a filler and weld over it. Another trick I have used is to save some of the 1/4" wide strip my power shears leaves behind when cutting out the patch panels. Because of the way the shear works the strip will have a slight burr along the edge. Cut a piece the length of the gap, bend it to the shape and slip the strip into the gap and push it in. The spring of the metal and the burr should hold the strip in place near flush with the outside surface. As with the wire, weld over the strip while welding the seam and grind off the excess on the back. NOTE: don't force the strip or wire into the gap or it could cause the panels to bulge up.

 

Heres a thought: why not make your own panel clamps? For each clamp cut a couple ~ 3/4"x 3/4" squares of sheet metal. drill a couple small holes near one another about in the center of the squares. Now bend a 6" length of the 0.025 filler wire into a narrow "U" and slide the wire ends thru the two holes in one of the squares. slide the wire ends thru the seam until the square is pulled flat against the seam. on the other side of the seam slip the wire ends thru the holes in the second square kinda like sewing on a button. Now twist the wires tight around each other with a pair of pliers until the seam is pulled together. Tack the panel just outside of the squares, then remove the "clamp" by snip the twisted wire, releasing the squares. Reuse the squares as many times as you'd like by just using a new wire! Since you are only putting the 0.025wire between the panels you will not have to deal with a wide gap like the commercial clamps make.

 

Clintonvillian
If you are asking me if I would not finish my inside welds I would have to say yes I would not, my inside welds look like drews and in my eyes they are very acceptable, now if you will see both sides than that is a different story, I finish them.
I made my own clamps out of 1x1 square stock used a store bought one to copy. Instead of using 16 ga for the draw plate I used 20 ga. I have no problem with the blowout using the gap method only have a problem if I stay on the weld to long, and I have learned not to do that to much. I use what is called stitch welding, where you weld one spot and the next spot is in the middle of the last spot. I never weld more than two spots in one place before I move to a spot on the other end of the weld so as not to put to much heat in any one spot letting them completely cool before I come back to them. The blue you see on the edges of the weld I try to keep it to an 1/8 to 3/16 if bigger tells me I am holding my trigger to long. This works for me may not work for everyone. Auto darkening helmets are a godsend to me. I really need to use this easy grind wire Ax is talking about, I just never think about it when I am at the weld supply house.

 

Is that stainless on the firewall and dash insert?
How did you finish the edge on the sides of firewall and dash insert where it contacts the existing dash?

 

I finish the inside of panels to the finish needed. I only fully finish inside if I'm going to skim coat it and paint it. I'll do the underside of fenders because most everyone is going to look under there to see if they can see how much repair work has been done. I'll knock off the excess bead on some places like the inside of a lower door skin replacement because Not matter how careful I am, that nearly flat panel is going to shrink/warp along the weld seam, and you can't hammer and dolly it, stretch and smooth it if the metal isn't close to the same thickness all along the seam. I have gone over my welding recommendations and methods in minute detail in my welding tutorial and the F1 fender rust repair thread.

gerrymoe don't wait a minute longer to get a spool of the Easy Grind wire, you'll never switch back again for any/all your MIG welding, it's is really that much better! However you'll need to use your phone or computer to get some, I'd be surprised, no make that completely shocked if you local welding supply has even heard of it, much less have it in stock. ONLY ESAB makes it, there is no equivalent in any other manufacturer's line. I can't count how many welding supply stores/salesmen when I've asked about it, tell me oh, I've got (something else) that's the "same"/"just as good"... Then when I push them if they have ever sold or used the ESAB Easy Grind They admit they had not. Then how the heck can they tell me the XYZ123 is just as good??? It's even hard to find on the interweb, These guys seem to be the only place that has it regularly : https://weldingsupply.com/cgi-bin/ei...DEF:OR:130PS43
It significantly more expensive (probably why no one stocks it) but well worth it! If you buy a spool of the 0.023 and don't agree, send it to me and I'll buy it off you.