Tech Corner: How To Fabricate Patch Panels Step-By-Step

The first time I attempted to fabricate patch panels was pretty frustrating. I just got done installing quarter panels on both sides of my project car and the quarter panel extensions I purchased were a bit too small. The problem was that only one supplier made the extensions, so I was pretty much stuck with what I had. I knew I had to add to the extensions. I also knew that I had no prior experience with fabrication and really didn’t have anyone to teach me. So, being as proud of a car guy as I am, I took the task on solo.

In the end, the panel came out fine. It took a lot of willpower to learn, but ultimately I gained a very useful skill. Whether the replacement part doesn’t quite fit or you’re combating a small area of rust repair, there’s a good chance you’ll need to fabricate patch panels at least once during a restoration. Learning to do it yourself can save you hundreds of dollars…or more!

To start, you’ll need some basic metal working tools. Body hammers, angle grinders, sanding equipment and a welder are the bare essentials. Additionally, a vice-mounted sheet metal brake will make bending the sheet metal much easier. Prices will vary, of course, depending on the equipment and materials you choose to purchase. But while it can be expensive up front, it’s well worth the investment in the long run.

Identify the Area in Question

Finding that an aftermarket panel needs to be modified is fairly straightforward since you’ll know right away when it doesn’t fit. If you’re fabricating patch panels due to rust though, you’ll first need to determine the extent of the damage. This means sanding down the rusted area to find out how deep the rot is.

Expose enough metal that way you know where to cut and have good, clean metal to work with. A variety of abrasive tools can be used to get down past the paint and primer to bare metal. As you’re sanding away, you may find rust has affected more than you originally thought. Check out our tech pieces on combating rust here and here, so you’re up to speed on the proper way to tackle and prevent future corrosion. It’s frustrating when this occurs, but you’ll need to find all of the rust so you can remove it and stop it from spreading.

Drafting/Cutting

After the rust has been exposed you can start identifying where to cut. Remember, you don’t want to fabricate patch panels that are more intricate than you need. So, before you cut, really think about the size and shape of the panel. Make quick sketches and draw a sturdy pattern for yourself. Once you feel confident with your sample, you can break out the cut off wheel.

It’s imperative that you take your time and give yourself a good, clean edge to work with. You don’t want to make more work down the line! Take care and move cautiously, as angle grinders can be very dangerous. We know… you may feel some remorse as you’re cutting up that old panel—man up. It’s worth it in the end. If you have the choice to save what you’re cutting off, do so, as it will help you later.

Gauging Steel

It’s important to use the same gauge of steel that was used on the original panel. You can use a gauge wheel to measure the thickness of the steel or a number of other tools designed specifically for this task. Once the old panel is cut away, you will have access to the area and can take your measurement. Then, once you have the right gauge of steel, you can move on to shaping your panel.

Shaping

Shaping the panel will take the longest amount of time. While shaping, it’s smart to make a piece that’s larger than what you will actually need. You can always cut it down to the appropriate size later. If you were able to keep the piece that you had to cut away, use it as a template to help out during this part of the process. Metal brakes and other shaping tools go a long way, but with patience and practice you can shape panels with basic hand tools such as body hammers. And remember that no two panels are the same, so you might have to get a little creative.

Additionally, as you’re shaping, be mindful of the type of weld you are going to perform to fasten the piece. A butt weld will make for the cleanest fit, so as you are shaping you will want to make sure the edges line up perfectly with the cut you made. Dry fitting and cutting will likely have to happen many, many times but it’s the best way to ensure a proper fit. And before you move on, bevel those edges to help with the welding process.

Welding

Once the panel is properly shaped, you can move onto welding. First, make sure the panel you’ve created is mounted securely in place. Double, then triple check it’s as perfectly lined up as possible before you start tacking. Using a MIG or TIG welder, tack weld it in place.

Once the panel is tack welded in, you can move to butt welding. To avoid warping the metal, Hot Rod Magazine suggests “three or four quick tack welds, followed by an air quench. … Move around the part so that consecutive welds are not next to each other.” This is another time consuming part of the process, but patience is key to make sure you fabricate patch panels of the best quality.

Grinding

After you have finished welding, you’ll have your own little diamond in the rough. Those built-up welds will need to be ground down for a flush finish. Angle grinders and other power tools emit a lot of heat during grinding so, again, take your time. The high heat can warp the sheet metal just like a welder might. As you’re grinding, take a moment every few seconds to let the metal cool down before proceeding.

Body Filler

After the welds have been ground down, you may still need to use body filler to finish shaping the panel. You also may find high and low spots primarily around the welded areas. This part is repetitive—and block sanding will make you crazy—but the key here is (don’t scream…) to be patient. After the body filler is set up and shaped, you’ll start to see things taking real shape.

Paint and Finish

After the body filler is applied, you can finally begin painting and finishing the panel. Small panels are often in discreet places that don’t require much paint for the finish. For the best results, I suggest using a paint gun. If you don’t have access to one, Dupli-Color Perfect Match paint can be used for the painting process.

Learning to fabricate patch panels is an extremely useful skill that will serve you well. Not to mention, it’s an incredibly rewarding creative process. As you move from step to step, you might find your own method of doing things and you should explore it. What I personally learned from building this skill was, you guessed it, patience. As much as we want to get the job done, it’s important to take time along the way and enjoy the nuances of workmanship. At the end of the day, it’ll make the finished product that much sweeter.

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