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Autobody Sheetmetal Repair

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by Jefferson Bryant  More from Author

What You Need to Know To Do It Yourself

So you managed to finally take delivery of that new project car, or maybe just decided the rust was getting too far gone to let it slide any further, either way, you need to work some metal. As the auto industry pushes toward more and more replacement-type body panels, locating a quality repair shop that is willing to work on old cars has become increasingly difficult. That’s not to say they are not out there – but they definitely are more expensive. A shop can make considerably more money swapping out hoods and fenders for insurance jobs than they can beating and welding on old metal. Faced with either paying someone else or tackling it yourself is a tough decision, especially if you lack experience. Replacing a fender or aligning a hood is simple stuff, this story is about the hard part – repairing damaged metal. If you are intimidated by working steel, that’s OK, but consider this – even the most experienced body man started not knowing anything. With the right tools and techniques, you can repair most damaged bodies in your garage.

 

Tools

There is an entire industry established for the purpose of building autobody tools, but in reality, all you need is a few basics. Spending money on elaborate specialty devices will empty your wallet faster than you can blink, and most of the time, they are unnecessary. Here are the basics that you need:

Hammer and Dolly Set – The dollies are about all the same, but the hammers are where you can go wrong. A cheap set has cheap hammers made with junk wood that split and the heads separate easily. Buy a quality set with a nice case that you can store them in.

Welder – Sheetmetal is thin. Rusty sheetmetal is even more fragile. The more settings your welder has, the better off you will be. Welding sheetmetal with a flux-core welder is tricky, you really need a gas-shielded MIG welder to save yourself some grief.

Basic Hand Tools – A set of pliers and a screwdriver go a long way in the world of sheetmetal repairs, keep a set on hand that you don’t mind getting burned up with welding spatter.

Air Tools – While not absolute necessities, working the steel without them is silly. You should have a DA (dual-action) orbital sander, an air-hammer with body-ripper and spot-weld buster tips, a die-grinder with Roloc sanding pads and a drill. You can use a cordless drill too.

Specialty Tools – It really depends on what you’re working with and how much of it you plan on doing. A plasma torch is incredibly useful in so many areas, once you have one, it is hard to believe you ever got along without it. An English Wheel/planishing hammer are great tools for fabrication, but if you are working on an early Mustang and just need to replace a section of the wheelwell, you don’t need it. One specialty tool that is really handy is the bead roller. Everything from rolling flanges to strengthening ribs and louvers – that is a great tool to have for serious body work, particularly in restorations and custom fabrication.

With the tools sorted out, there are a few techniques you need to learn. Using a hammer and dolly is not easy, it takes time to learn. While you may want to start by smacking the backside of the dent, but a hammer and dolly is designed to shrink the metal, you actually start by tapping the extremities of the dent on the outside (while holding the dolly to the inside of the panel) and work your way into the center.

Another critical technique for body repair involves proper welding. Sheetmetal warps quickly, the more heat you put into it, the more it will warp and buckle, requiring more hammer work and body filler. Stitch welding reduces the amount of heat put in the metal, not only reducing the warp factor, but also limits burning holes in the metal as well. Stitching is done by laying out a series of small tack welds about 2-3 inches apart along the length of the repair. Once at the end of the joint, you go back and start another series at the edge of the previous weld, you end up with a fully-welded seam that has less warpage. You can assist the cooling period by blowing compressed air over the welds to cool. This is especially helpful in smaller repairs.

The key to any successful body repair is patience. Take your time and learn from your mistakes along the way. Always measure at least three times before you cut, and always wear safety glasses. With practice, you will be saving money at the body shop and can take pride in the fact that you did it yourself.

 

 

A good selection of quality hammers and dolly tools is a good investment. We do know a few body guys that use a plain old carpenter’s hammer for everything. The large yellow polyurethane hammer is great for getting in tight spots with compound curves. On the bottom left is a trim anvil, which is used for straightening dented trim. We use a hammer and dolly set from Gearwrench that has maple wood handles and top-quality heads and dollies and it comes in a nice molded case for storage.

 

An English wheel certainly has its uses beyond fabrication. Here a ’40s Ford fender is smoothed out. The circled areas had about 30 small outward dents and the wheel made easy work of them.

 

A planishing hammer is a mechanized hammer and dolly. The anvil (bottom) is interchangeable with different radii; the heavier the radius, the more shaped the bend imparted to the metal is. The hammer (top) is flat and on this model from the Eastwood Company is actuated by a foot-controlled air hammer.

 

Replacement sheetmetal can be found for most makes and models, but often only in sections. This floorpan for a ’51 Ford Shoebox came in three pieces, which have to be sectioned together in the car. This is one of the trickiest jobs for the beginner.

 

If your car doesn’t have new metal available, you have to make it. A bead roller is a versatile tool that you can use to make your panels. A bead roller uses two dies – a male and female – that attach to geared spindles so they rotate, pulling the metal into the dies. The depth is adjustable and can make straight lines or intricate curves. The one thing you really want in a bead roller is a foot-controlled motor. This unit is hand-crank driven and requires two people to operate efficiently.

 

We made this trunk panel repair section to match the corrugations in this rusted out floor. Once welded in, you would never know that is wasn’t original.

 

Air tools are really handy for body work. This punch/flange tool from Astra punches a clean 3/8-inch hole in sheetmetal up to 16-gauge, which is the perfect size for spot welds.

 

The other side of the Astra tool crimps a 1/4-inch wide by 1/16-inch deep flange on the edge of the sheet. This is ideal for lap joints shown here. While a butt-joint looks better from the backside, it is not any stronger and much more difficult to produce. Lap joints allow for some adjustment room, which is always a good thing for the beginner.

 

A quality welder is essential. This is a Miller Millermatic 211 that features Auto-Set. You simply select the wire size and the metal gauge and it automatically adjusts to the proper settings. There is room to tweak the current flow, and you can always set the wire speed and amperage yourself, but Auto-Set works really well. Plus this is a dual-voltage welder, it works on 120v and 230v. For the best results, use a true gas-shielded welder for thin sheetmetal, it is much more consistent. Flux-core welding has it uses, but you get a lot of welding spatter, which has to be cleaned up later.

 

This is a stitch weld. As you can see, there are groups of smaller welds in a series. This is about seven passes, using air to cool the metal along the way. Small repairs and long, straight seams such as this quarter-panel are prone to warping with just a little heat.

 

Welding up trim holes (or holes from dent pullers) can be a bear. This copper spoon from Eastwood allows you to fill the hole with weld, steel welding wire won’t stick to copper, making it super easy. Eastwood has several types of spoons, including magnetic strips that hold the copper in place so you can use both hands.

 

Larger holes, such as this door handle mounting hole require filler metal. We used a magnet to hold it in place while it was tacked in position.

 

When working on a floorpan or rocker panel replacement, it is always a good idea to brace open sections, such as the door jambs. As seen on this ’51 Ford, the entire floor pan and rocker had been removed. Even though the car has a full frame, the body can shift and get tweaked; if that happens, the doors will never fit right. We used a piece of square tubing and tack welded it in place. If you don’t want to weld on the door jambs, you can use clamps and bars, but welding it is more stable. This is even more crucial on unibody cars like Mustangs.

 

Most welded-on body parts are secured with spot welds, often in the middle of a large panel, making it impossible to separate easily. This tool is called a spot weld cutter from Rotabroach. This specialized cutter cuts on the outside of the spot weld, separating the two panels. These are more expensive than the spot-weld drill bits, but they last much longer and are more versatile. However, the drill bits typically only cost a few dollars for three bits.

 

Before setting the new panel in place, you need to protect the underlying metal. This goes for new and old structures. The red paint you see here is weld-through coating, which has a high Zinc content and protects the fresh welds from rusting. It is also a good idea to coat the inside of the braces with undercoating. Welds are prone to rusting, the process leaves the metal completely unprotected. This is an important but often overlooked step.

 

Whenever possible, replicate the factory welds. This floorpan was originally welded to the sides of the car, but the braces in the center are part of the car’s subframe. This connection is critical for safety. Note the welder’s foot on the pan, this puts pressure on the metal to ensure a tight fit with the subframe.

 

Once welded, all of the seams get coated with seam sealer. This fills the pinholes in the welds as well as any gaps. Just like the weld-through primer, this is a critical step for long-lasting factory appearance.

 

Cleanliness is important for body work. Even brand new steel must be wiped clean with general-purpose thinner before body filler or paint is applied.

 

Working body filler requires some tools as well. A DA (Dual-Action) orbital sander (center) helps make quick work of rough filler, and then you will want to move to a leveling block like these shown here. The large green block has steel rods in the center that can be removed to allow the block to flex with the panel.

 

This is what a finished smooth body filler job will look like. The edges are feathered out to the rest of the panel and it is nice and smooth. Here is a tip – when sanding with a board, move in a diagonal pattern across the panel, front to back and side to side, don’t work the panel in straight and down sections. This creates waves and will ruin the final finish. About 120-grit is what you are looking for with a first-primer surface.

 

This is the same Mustang hood in the previous picture, right after primer. Note at the center left that the body filler is a different color sheen as the rest of the hood. Body filler soaks up primer, whereas metal and gel-coat (this hood is fiberglass) do not, giving it a dry look. This is the reason for primer (other than getting paint to stick). The hood will need to be sanded smooth, sprayed with a sanding primer (and sanded again) to fill the imperfections and provide the uniform finish that you need before spraying paint.

 

M&F

 

Sources

Eastwood Company
(800) 343-9353
www.eastwood.com

GearWrench
Danaher Tool Group
(800) 688-8949
www.gearwrench.com

Miller Electric Manufacturing Co.
(920) 734-9821
www.millerwelds.com

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