Sometimes rust can be glaring at a person in the face. Its unsightly presence is what probably spurred the car-owner to take it to the mechanic in the first place. However, rust has an uncanny ability to duck and hide itself in places which the owner may not have imagined. A good method in uncovering where rust may be located is to look for bubbles in the metallic work or simply knock gently with the pick-end of a body hammer on any area you may suspect to have rusted. If you knock a hole into your precious bodywork, “don’t stress”, because its better you discover the flaw now than allow the rust to assert its exponential growth on your car at a later stage.
If rust is a common thing in and amongst the vehicles of your family and friends, then you may want to consider purchasing these items as an investment to treating rust in the future. If you simply wish to repair the rust on your car as a once off thing, then maybe the borrowing of these items would be in order or perhaps it would be more prudent to simply send your rusty car off to the mechanic. The cost/effort option is ultimately up to you.
-You will need sheet metal (preferably the same gage as the metal of your car). If you do not know the metal gage of your car, you will also need a 5 inch air grinder loaded with a 40 grit disc.
- You will also need an air compressor and a die grinder with multiple cutting blades.
- Finally, you will require a MIG welder with gas and wire as well as a metal gage checking tool.
Firstly you need to determine the exact area that needs removal and repair. This can be done by tapping the affected area with a hard object until all rust and weak metal is flaked off and removed. Once you are 100% certain that all rust is gone, get a permanent marker and draw a line, approximately 2 inches into the good metal all the way around the rusted area. This is done to make sure that all signs of the rusted area will be effectively removed.
With your cutting line clearly marked by the permanent marker, you can plug your grinder into the air source and begin cutting. Try not to cut all at one time. Rather, try putting a light cut on the marked area and running your grinder along the permanent marker line until the full surface area of the intended cutting region is fully removed.
Using the piece of metal which was skillfully removed from the rusted portion of your car, place that piece of metal on the metal sheet (as a measurement indicator) and cut out a similar sized piece of metal with the grinder.
Next, using the 5 inch grinder with the 40 grit disc, lightly run it over the back of the newly cut metal until all the burs are gone. Then, run the grinder along the exposed section of metal of your car from where the cut-out piece of metal came.
Now take the good piece of metal that you cut from your sheet of repair metal, and fit it in the hole that you cut out of your car. Vise-grips are generally quite good tools that can be used to hold the new piece of metal in place.
The next step involves the use of the welder so ensure that you have located a good spot to put its grounding clamp. Once the gas in on, and you’re certain that the vise grips are securely fastened to hold the metal in place, you will need to run a 1 inch bead on the top, bottom and side sections of the metal piece. This will ensure that the piece of metal is securely fastened to the metal surface of the car. You may then remove the vise grips.
Continuing the welding process could take a bit of self intuition. A welder is by nature, hot, and able to render any metal surface soft 
and malleable. You therefore need to ensure that a single portion of your car is not overexposed to too much heat as this could warp the metal surface. To avoid this problem, try welding a 1 inch bead at the top followed by a 1 inch bead at the bottom and continue this process until there is one continuous bead all the around the metal piece. Try cooling off a single bead with a little air before moving on to the next bead. Remember, one bead on top, one at the bottom, one at the top, one at the bottom.
Once the welding is done and the metal is cooled, use your 5 inch air grinder with the 40 grit disc and grind the welds flat. You should not even be able to see the welds if the grinding is done correctly.
Job complete.
Referances: www.hubpages.com, www.smash-repair.com