Those things are a little difficult to install 'cause there is no square or solid point of reference to hang 'em by. The key is to use as much original body metal as possible and as little patch panel as possible. You may end up using only a small fraction of the entire patch panel. If you are needing to replace a piece approaching half a panel, best bet is replace th whole quarter panel. Small patches are fairly easy and whole panel replacement is fairly easy. Big partial patches are really difficult. Cut out the old body piece shy of the margins around the new one. Make your cuts square and straight as possible. Then tack the new one overlapping the old panel and stand back and look. Use a straight edge and whatever else you can find to make sure the panel conforms to the body. I have yet to find one of those that didn't need significant reshaping, mostly simple bending to achieve the proper curvature. Once you are happy with the fit, scribe the new panel using the smaller opening in the body and cut to the scribed line. It should be ready to butt weld in perfectly.

 

What's your preferred tool for cutting the scribe line once you have drawn it? It has to be pretty precise to make a perfect butt weld and I would think an air nibbler might actually distort the metal a bit and chew into some places you don't want chewed. Also not good for tight corners and curves. Air saws (scroll saw type blade) have a tendency to catch on the metal edge from time to time and create some nasty distortions. Metal cutting wheels cut nice but are difficult to control and keep on a straight line...and they can't be used at all on sharp curves and bends. Is there a better option than any of the above? Or, in the alternative, which of the above should a person just learn to deal with.

Dewey

 

a small airsaw gets my vote for cutting patch areas, the thinner the blade the tighter the radius it'll be able to cut. I couldn't live without one doing this stuff. a 1/32 thick 3" cuttoff wheel works good for straight cuts. air nibblers distort the metal--any time there is a shearing action the edge will be stretched and distorted to a degree. Cutting actions that remove material like the saw and ctoff wheel do not distort. Plasma cutters work good but I have problems with accuracy. On very large sections I overlap the repair panel on the existing metal by a half of an inch and attach with temporary fasteners-screws. Then take the airsaw and trim away the overlap about 8 inches at a time and follow with the welder. The overlap section being removed must be pulled away as you go and slight adjustments to fit may be necessary with hammer and dolly, but if it is done slowly it works extremely well. Cut 8 inches, pull away the piece trimmed off, weld about 4 inches, cut some more, pull the trimmed piece away, weld again and continue till it's all welded up. Then go back and weld your screw holes shut. Trying to hold a large section from flopping around while aligning and welding can be very frustrating othersise. JMO

 

baddbob,

Just so I understand your technique. I assume you first place the patch panel behind the existing body panel and scribe a cut line (and possibly even drill the screw holes???) Then you move the patch panel to the front side of the existing body panel and screw it in place. Then you run the air saw right along the scribe line - but only cutting the patch panel, not both panels.

Is that about right?

Dewey

 

You can do it that way as it is easier to remove the piece that you're trimming away, but I usually place the patch piece over the exhisting sheetmetal and just trim along the edge of the patch cutting the overlap from the original sheetmetal, it helps if you can reach to the backside to pull the trimmed piece away from the seam as you cut. Sometimes I drill a hole through the end of the piece that will be trimmed away and attach a length of wire so I can pull it away as I cut. Like when installing half quarters on some models it is almost impossible to reach in the front area so in this case I use the wire and run it out the trunk opening where I can pull on it. Hope this makes sense to you. The screw holes need to be predrilled in the panel and the panel needs to be testfitted and adjusted to it follows the contour good before you start cutting and welding. As you cut you'll see the two pieces of metal almost align them selves with the thickness of the saw blade gap in between, I weld from one end of the seam to the other and the weld pulls this gap (1/32") closed as I go, You'll need to remove the screws as you cut in order to pull the excess metal away from the seam. On smaller patches I don't use this method but for large areas it works really well IMO.

 

And do you have any special techniques for small panels? How do you do those?

 

Both of these guys gave you some great info, here is another version using basically the same techinques.

If I were doing a patch, the first thing I want to do is cut the bad part out of the panel on the car. Let's say, the wheel arch is rusted on you car so you want to replace all around the wheel arch and out onto the panel five or six inches. I am NOT saying this is how far you would go, Willies covered how far well. I am just talking about how I would trim.

With the wheel arch and a few inches of the old panel removed. The wheel house would be cleaned up well, hammered and dollied on the edge so the mateing surface under the lip is as nice as it will be. I would then decide exacty how far I am going to go up and out. Trim the patch to that size, being sure NOT to cut less than I have already trimmed from the old panel (you only do that once ). I then fit the patch up to the wheel house and clamp it as it will be when it is welded. This is VERY important, you must clamp it in WHERE IT WILL BE WELDED, the butt weld line has to be precise.

With the patch clamped in place I use a sharp scriber and scribe a line along that patch panel into the old panel PERFECTLY tight up against the patch panel. Then remove the patch and cut up to an inch or so of the line with a "minimal distorting" tool like a die grinder with a cut off wheel, an air saw, or nibblers or electric sheer. After that I take right hand shears and cut a perfect cut right on that scribe line from right to left just starting the cut anywhere I can by going up at an angle thru the inch I am cutting off up to the line. Then I use a left hand shear and come from the left to right starting on that line already cut and trimming off the other side of the one inch I left when I started my cut from the first right to left cut. In other words there is no reason to start from the end or drill a hole or something like that.

This will leave you a near flawless seam. I will use a file to make it flawless. I weld these seams with a jewelers torch with .023 Mig wire for filler rod, that is how close you can get that butt weld seam.

 

Another tip for locating a panel is to use the flexible shape pattern method that Wray Schelin uses.. described at: www.metalmeet.com You use a low stick transfer tape and fiberglass reinforcing tape to make the pattern.

You can make a 3d pattern that exactly fits the other side of the car, and use it to fit the panel by turning it inside out...maybe even more accurately than original.

John www.ghiaspecialties.com

 

I'm using a die grinder with a cut off wheel, it kind of takes some time. I already cut off the main area before I posted, so as far as just taking off the bad parts, I'm kind of screwed. Thanks for all the tips, I have it close enough now to do all the fine tuning you guys mentioned. The tape method seems especially interesting.