This afternoon I did some amateur metalworking to try to straighten the dent in the passenger side door. The door has clearly been the victim of some kind of collision and when I stripped the paint there was lot of body filler under there.
I plan to do my bodywork in the following steps:
- Use body hammers, dollies, slide hammers, and other tools to attempt to pull the dented metal back to flush with, or in some cases proud of, the surrounding un-dented metal.
- Use friction and heat to shrink any metal high spots from my metalworking back to a uniform surface.
- Fill the majority of remaining voids with lead-free body solder to build up the area, once again slightly proud of the finished surface.
- Grind and sand the body solder as flush to the surrounding metal as possible.
- Apply the thin coat of body filler, sand, repeat…as necessary to get a perfectly smooth surface.
My goal is to minimize the use of body filler to a thin coat, maybe 1/16 to 1/32″ and to make the repair as strong as possible. Today’s body fillers are incredibly strong and bond very well to metal, but I still think the body solder has an advantage in bonding and strength.
Here are head-on and profile pictures of the dented door.
In order to find the boundaries of the dent, i.e. the low spots, I marked over the surface of the door with a black marker. Then I used a flat sanding block to sand the area, so the low spots would remain dark black.
Here is a shot of the low areas out in the sun where it was easier to see.
Where the dent had been repaired by the previous owner there were a couple of holes in the door skin. I used these and my slide-hammer to pull the metal up. When it became clear that the pulling wasn’t popping the dent out but just forcing up localized areas, I drilled a few more holes in order to pull in more areas.
I kept pulling, and adding holes to get the whole area up flush or slightly above the surrounding door area. The metal had been stretched when the dent happened, and I stretched it up in the opposite direction. No question this was the ugliest part of the repair process.
Next I brought out my new shrinking disk. I bought this shrinking disk on ebay from Wray Schelin, who runs the Metalmeet forums, which are really great for discussing metalwork projects of all kinds including metal repairs. There are some real artists and craftsmen over there. The disk is steel and 9″ in diameter and I paid $35. The edges are bent up so it won’t slice your flesh if you get it too close to your body, which is a nice feature. It is mounted to a large grinder, in my case a 7″ angle grinder from Harborfreight. The grinder should have at least 6000 rpm in order to work effectively with the shrinking disk.
The shrinking disk is used to build up friction on the surface of the metal, specifically on any and all high points, making the metal very hot in those areas. After the heat is built up, the idea is to quench the metal with water. The heating and quenching process causes the metal to shrink. The shrinking disk is large enough so that if you run it along the surface of the metal it will only heat up the high points so eventually they should shrink down flush to the original metal.
Here is the shrinking disk and a picture of me running it over the door.
After running the disk on the surface for 15-20 seconds or so, I quenched the metal by squirting water on it. The metal sizzled and steamed a bit, confirming that the heat was building. I avoided getting the metal too hot, and making it change to red or blue (which is unnecessary), by only running the disk maybe 30 seconds at a time before quenching. Here are the results after the first shrinking.
The process took patience. I continued the cycle of shrinking and quenching, shrinking and quenching. 30-seconds on the disk, and then quench. After thirty minutes of this process, here were the results.
Then I continued the shrinking and quenching. After fifteen more minutes, I could tell I was making progress.
Finally, after sixty minutes of shrinking I could tell the improvements I was getting were diminished.
So I put down the shrinking disk and welded up the holes in the door. I used my 4 1/2″ angle grinder and some cut-off wheels to grind the welds smooth.
Then I cleaned off the whole area and treated it with some Metal Prep. There are certainly some low spots remaining, which I will fill with solder, but in general the low spots are much smaller and less deep. And perhaps more importantly, the metal is no longer stretched inward and won’t “oilcan” in and out when you press on it.