This wasn't originally intended to be a Gassavers How to post, but turned out to have information that others here might like. The number of pictures is staggering. I know, I had to upload them. It isn't exactly a gas mileage car that was done, but rust applies to everyone.
Please take all the necessary precautions for safety. Wearing eye protection, ear protection, gloves, and full face masks as well as long sleeves when grinding are recommended. You will be working with sharp metal throughout this process.
This post will probably raise as many questions as it will answer.
To go along with the explanatory pictures (see the URL below), these are the steps I took:
1. Assess the damage: How bad is it; how much is in a replaceable panel; how much in a fixed portion of the vehicle shell; can you access both sides of the damaged area; does it require cutting out or just cleaning; is there wrinkled metal that needs to be straightened first. As you will see, this particular car has many different types of damage and required just about every form of fix. There are many tools required to fix such a vehicle and I am sure most people don't have access to all of them. But there are many ways to fix the same dent and/or rust hole. Due to the fact that this vehicle is a high dollar classic the repairs that were performed took the foundation right back to metal instead of patching with body fillers and/or glued on panels. That's not to say that there isn't a time or place for those processes
2. Decide which tools are required. Are you going to cut out the damage? If so, you can use an abrasive cutoff wheel on a die grinder, or drill a hole with a drill and use handheld snips. Plasma cutters work well in some areas, but can light things on fire on the other side if it is not protected. They sell power sheetmetal shears that hook onto the front of a drill motor and reciprocating saws like Sawsalls, to name just a few.
I used, predominantly, an abrasive cutoff wheel on a die grinder. It cuts with low heat transfer to the sheet metal and allows you excellent control when cutting a straight or semi-curved line. I like to use green painters' lacquer tape to tape an accurate cut line (as was the case on the upper body line on the 7 1/2 foot quarter panels). I then used half-inch wide painters' tape to allow a half-inch margin for overlap of the new fender skin over the old.
For spot weld removal I drilled out the spot welds with a drill and bit that was larger than the entire spot weld.
For removing sharp edges and spot weld ridges I used a 4 1/2 inch handheld angle grinder with blue aluminum oxide flapper discs.
To clean rust from the surface, wire wheels on a die grinder work very well. I like the twisted bristle wheels the best since they have less of a tendency to throw bristles and stab you. I use a selection of shapes that are sold at any hardware store.
3. Acquiring chemicals for cleaning and protecting: Again there are countless numbers to choose from. I like to mix a solution of Metal-Etch because it cleans the remaining rust off the surface and in pits. Once that is dissolved with a water rinse and dried, I like to convert the remaining rust with Rust-mort. It turns rust into magnetite at a molecular level. Once it is nullified as per manufacturer instructions, I then spray the surface with a metal etching primer. At this point, a high build primer can be used and/or any body fillers that may be chosen. Paint preference, of course, is up to you. I like to use Rustoleum XO Rust Hammered finish paint in areas that require toughness and excellent corrosion resistance.
4. If welding is required: I prefer a MIG welder when welding sheetmetal such as that on cars because when used properly it transfers the least heat to the smallest area possible. That keeps the panels from warping where other welding systems transfer more heat to larger areas of the metal. The pattern I use starts with clamping the new piece firmly to the parent metal. I cannot stress enough how important it is to generate a perfect fit before any welding takes place. If you have a gap, for instance, the weld pool will shrink the metal and pull it toward itself causing warping or undulations in the metal that will have to be smoothed out.
Tig welding would be my second choice. Although it transfers more heat, the weld bead is softer and easier to grind and form with hand tools (hammer and dolly) when straightening the inevitable warping.
Oxy/fuel welding generates the most heat to the greatest area warping the panel the worst. However, it anneals the metal in the process making it the easiest to straighten.
Often, low amperage MIG welders of reputable name brands, for example, Miller or Lincoln that weld up to 3/16 to 1/4 inch thicknesses do best because they don't have a tendency to overpower the sheetmetal and blow holes in it. Additionally, they are usually one of the least expensive systems to get started with.
So now you have what you need, this is what you do:
(We will use the tail light on the right side of the Dodge Charger as an example.)
First: Assess the area to be removed. Take measurements and make sure you have the metal for the patch panel.
Second: Tape your cut lines. Again, I cut with an abrasive cutoff wheel on a pneumatic die grinder.
Third: Cut, making sure to wear glasses and a full face shield, ear protection, gloves, and sleeves. It is amazing how sparks still find their way under all that.
Fourth: Remove any spot welds as necessary.
Fifth: Grind with wire wheel and clean with chemicals any adjacent parts that remain.
Sixth: If any surfaces overlap, seal with weld-through primer if welding is to be done in that area.
Seventh: Create new patch panel. With a little practice and some junk you have sitting around the yard or in your local wrecking yard, you will be amazed how with a hammer and a few pieces of pipe and/or any other dolly surface you can find (I use a railroad rail as an anvil) you will be able to form the necessary shape into your patch panel. If the patch panel is predominately flat, you will not need to cut it too excessively large. Just make it about a quarter inch on each side larger than the hole it is to ultimately fill. If it has a lot of shape, it may be necessary to make it as much as an inch larger on each side.
Eighth: Test fit and retest fit. Cut and trim. Reshape, alter, and retest fit. This where it is important that the piece fit as perfectly as possible.
Nineth: Prime all overlaping mating surfaces with weld-through primer. This provides sealed surfaces in between layers.
Tenth: Install and clamp new patch in place aligned as perfectly as possible.
Eleventh: Tack weld in an alternating pattern, skipping from one corner to another and then space tacks about an inch apart between previous tacks while still alternating from side to side. Make sure the meeting edges are truly level with one another.
Twelveth: Using small trigger bursts with a MIG, stitch weld from one tack to the next altering from edge of patch to edge of patch until you have welded all the way around the entire panel.
Thirteenth: Grind off excessive weld bead. I like to use the blue aluminum oxide flaper discs for this. It generates less heat than a stone wheel and is easier on the adjacent sheetmetal.
Fourteenth: Prime the finished patch with metal-etching primer and move on to any other body filler and/or high build primer as necessary.
When you go to the URL click on the '69 Dodge Charger Album