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View Full Version : Lower Fender Patch Panel fitment and welding



MP&C
12-28-2013, 08:37 PM
I had a fender patch job that came in the shop, so we took quite a few pictures to hopefully make a good tutorial. While this fender may be a bit newer than you guys may need, the fabrication and fitment details should prove well worth the read.


The owner had done a first time attempt and wasn't happy with the results, so I offered to help him out. He lives in Richmond which is about a two hour drive from my shop. Zach showed up in the Biscayne, which really helped out to have a good pattern in the adjacent panels to work against. He was originally going to just bring the fender, but I think after all is said and done we can see that would not have worked as well.

Here is what we had to work with.

http://i5.photobucket.com/albums/y167/rmccartney/Metalworking/Picture001-2.jpg

Where he had done a nice job of trimming his replacement prior to welding (especially for a first timer):

http://i5.photobucket.com/albums/y167/rmccartney/Metalworking/4626439887_ea5b112675_o.jpg

..........I think a lot of the problems he experienced was due to not testing the welder set up on some scrap pieces first, and some weld contamination from residual rust scale that should have been removed.

In trimming out repair panels for fenders, I have always tried to install a new flanged rear edge in order to minimize the vertical welds. The more welds, the more shrinkage, the more possibility of the panel moving. Where we could planish out the welds in an attempt to counter some of this shrinking effect, that is not possible behind the fender brace, so what he ended up with was this:

http://i5.photobucket.com/albums/y167/rmccartney/Metalworking/Picture002-2.jpg

......where you can see the replacement patch has pulled in a couple different areas to noticeably widen and distort the door to fender and rocker to fender gaps. I point these out not to pick on his work, but to highlight the possible effects of installing the patch in this manner that perhaps another method should be considered.

Where the vertical weld seam on the right side was clear of the brace to allow for planishing the welds, this had not been done and serves as a good demonstration as to how the metal will shrink. If we were to look at the profile of the lower fender from the side, it appears much as an arc (to simplify things). Due to the heat from welding and the subsequent shrinking, the result in the case of an arc will be for it to lose its radius to form a straight line. In this case (as in most cases), what we see is a valley down through the middle of the weld as the shrinking pulls the adjacent panel along for the ride.

http://i5.photobucket.com/albums/y167/rmccartney/Metalworking/Picture005-2.jpg

Prior to removing the fender, it was marked with a reference line to be able to duplicate the rear edge location once a new patch was fitted into place. Where the fenders rear edge had distorted, the mark was measured from the door and rocker edge to provide for a consistent door gap.

http://i5.photobucket.com/albums/y167/rmccartney/Metalworking/Picture001-2.jpg

The fender was removed and Zach mastered fairly quickly the fine art of spot weld removal using a cutoff wheel. You can plainly see as the outer layer gets hot (speed is required here to generate heat), especially pronounced when the layer begins to thin, it will turn blue in color. When you begin to see the silver color of bare metal right next to the blue, you are now into the second layer. Time to stop there, grind a bit more around the perimeter of blue, and gently pry to check if the panel will release.

http://i5.photobucket.com/albums/y167/rmccartney/Metalworking/Picture006-1.jpg

http://i5.photobucket.com/albums/y167/rmccartney/Metalworking/Picture007-1.jpg

For a more thorough tutorial of spot weld removal using this process, here is a video:

http://s5.photobucket.com/user/rmccartney/media/1955%20Chevy%20Wagon%20Restoration%20Album%203/RemovingSpotWelds.mp4.html


Where the lower flange of the fender had some rust issues of its own, we had to duplicate the contour around the lower mounting bolt.

http://i5.photobucket.com/albums/y167/rmccartney/Metalworking/Picture009-1.jpg

http://i5.photobucket.com/albums/y167/rmccartney/Metalworking/Picture010-1.jpg

http://i5.photobucket.com/albums/y167/rmccartney/Metalworking/Picture011-1.jpg

http://i5.photobucket.com/albums/y167/rmccartney/Metalworking/Picture012-1.jpg

http://i5.photobucket.com/albums/y167/rmccartney/Metalworking/Picture013-1.jpg

http://i5.photobucket.com/albums/y167/rmccartney/Metalworking/Picture014-1.jpg

http://i5.photobucket.com/albums/y167/rmccartney/Metalworking/Picture015.jpg

The lower flange was bent and the new weld seam was moved slightly to the right to remove some of the valley more easily and to also provide more room for planishing both the weld and the HAZ (heat affected zone) adjacent to it.

http://i5.photobucket.com/albums/y167/rmccartney/Metalworking/Picture017.jpg

http://i5.photobucket.com/albums/y167/rmccartney/Metalworking/Picture018.jpg

http://i5.photobucket.com/albums/y167/rmccartney/Metalworking/Picture019.jpg

The fender was refitted (one of many times) to insure the distortion had been removed and we had a nice straight panel in alignment to the door...

http://i5.photobucket.com/albums/y167/rmccartney/Metalworking/Picture021.jpg

Then the patch was aligned to the lower flange mounting hole, trimmed to fit, clamped in place, and marked for the fender rear edge flange.

http://i5.photobucket.com/albums/y167/rmccartney/Metalworking/Picture022.jpg

To show what is possible using "basic" tools, and since the bend is not perfectly straight, a short section of wedge "anvil" was clamped in the vice and a low crown hammer used to gradually form the bend. A shrinker also came into play to duplicate the "arc" profile of the fender, and this was checked to the front edge of the door....

http://i5.photobucket.com/albums/y167/rmccartney/Metalworking/Picture027.jpg

http://i5.photobucket.com/albums/y167/rmccartney/Metalworking/Picture028.jpg

http://i5.photobucket.com/albums/y167/rmccartney/Metalworking/Picture029.jpg

http://i5.photobucket.com/albums/y167/rmccartney/Metalworking/Picture030.jpg

http://i5.photobucket.com/albums/y167/rmccartney/Metalworking/Picture031.jpg

Then the patch was welded to the fender. I normally use weld "dots" in Mig welding sheet metal, and the machine gets set a little hotter to insure full penetration welds, and wire feed speed a little faster for less chance of blowout. Then the weld dots will be planished out, ground down just above flush (gets them out of the way for planishing the next set) and then planish the HAZ next to the welds as required. The top right cut was done using a large radius, which helps to reduce the shrinking effects that get compounded when working in a tight 90 degree corner. Where the inside radius will still shrink a bit more than the outside, the radius does make it considerably more manageable.

http://i5.photobucket.com/albums/y167/rmccartney/Metalworking/Picture036.jpg

http://i5.photobucket.com/albums/y167/rmccartney/Metalworking/Picture037.jpg

http://i5.photobucket.com/albums/y167/rmccartney/Metalworking/Picture038.jpg

http://i5.photobucket.com/albums/y167/rmccartney/Metalworking/Picture041.jpg

http://i5.photobucket.com/albums/y167/rmccartney/Metalworking/Picture042.jpg

http://i5.photobucket.com/albums/y167/rmccartney/Metalworking/Picture043.jpg

http://i5.photobucket.com/albums/y167/rmccartney/Metalworking/Picture044.jpg

http://i5.photobucket.com/albums/y167/rmccartney/Metalworking/Picture048.jpg

http://i5.photobucket.com/albums/y167/rmccartney/Metalworking/Picture049.jpg

http://i5.photobucket.com/albums/y167/rmccartney/Metalworking/Picture050.jpg

http://i5.photobucket.com/albums/y167/rmccartney/Metalworking/Picture051.jpg

We did wind up with a slight depression right over the brace where we should have put a bit more crown in the panel. All in all, quite an improvement and a good hands on lesson for the owner. Once Zach gets it all painted up it should last him quite a few years to come. I think he has a much better appreciation for working with sheet metal now..

MP&C
12-28-2013, 08:38 PM
Here's a 55 driver's fender that had a substandard repair of spot welded galvanized sheet metal. Once the patch was removed, we see it has more rust action beneath, so the damaged area is cut out large enough to clear the fender brace on the vertical weld seam.

http://i5.photobucket.com/albums/y167/rmccartney/1955%20Chevy%20Wagon%20Restoration%20Album%202/Picture127.jpg

Hindsight, the upper left corner should have been cut in a sweeping radius to minimize the compounding effects of shrinking in a tight 90 degree corner. That's another reason I showed the previous post first, to show the correct method..

http://i5.photobucket.com/albums/y167/rmccartney/1955%20Chevy%20Wagon%20Restoration%20Album%202/Picture128.jpg

The repair piece is started by bending the rear flange, and cutting the relief for the lower bend.

http://i5.photobucket.com/albums/y167/rmccartney/1955%20Chevy%20Wagon%20Restoration%20Album%202/Picture129.jpg

The lower bend is made using a 1/4" radius die in the press brake, but can be done with incremental bends in a regular brake.

http://i5.photobucket.com/albums/y167/rmccartney/1955%20Chevy%20Wagon%20Restoration%20Album%202/Picture138.jpg

http://i5.photobucket.com/albums/y167/rmccartney/1955%20Chevy%20Wagon%20Restoration%20Album%202/Picture131.jpg

Some shrinking and stretching of the rear flange on the Lancasters will start to shape the rear edge.

http://i5.photobucket.com/albums/y167/rmccartney/1955%20Chevy%20Wagon%20Restoration%20Album%202/Picture134.jpg

Followed by some "gentle" bends in the press brake again to match that contour across the piece.

http://i5.photobucket.com/albums/y167/rmccartney/1955%20Chevy%20Wagon%20Restoration%20Album%202/Picture133.jpg

Test fit:

http://i5.photobucket.com/albums/y167/rmccartney/1955%20Chevy%20Wagon%20Restoration%20Album%202/Picture135.jpg

http://i5.photobucket.com/albums/y167/rmccartney/1955%20Chevy%20Wagon%20Restoration%20Album%202/Picture137.jpg

Then the inner fender brace was sandblasted, and with no holes showing up in the pitted areas, the brace was epoxy primed along with the inside of the repair panel.

http://i5.photobucket.com/albums/y167/rmccartney/1955%20Chevy%20Wagon%20Restoration%20Album%202/HPIM6287.jpg

http://i5.photobucket.com/albums/y167/rmccartney/1955%20Chevy%20Wagon%20Restoration%20Album%202/HPIM6288.jpg

http://i5.photobucket.com/albums/y167/rmccartney/1955%20Chevy%20Wagon%20Restoration%20Album%202/HPIM6289.jpg

Give the epoxy primer a few days to cure before welding as it makes it more tolerant of the heat.
Now to finish the lower fender. The first order of business is to clamp the lower edge once flush with the bottom, align the side, and tack weld in place.

http://i5.photobucket.com/albums/y167/rmccartney/1955%20Chevy%20Wagon%20Restoration%20Album%202/HPIM6336.jpg

It helps to planish out the weld tacks as you go to counter the effects of the shrinking. This will minimize any puckering and pulling of the panel.

http://i5.photobucket.com/albums/y167/rmccartney/1955%20Chevy%20Wagon%20Restoration%20Album%202/HPIM6337.jpg

With any welding you are doing, check the back side to insure full penetration, or adjust your machine accordingly. If you need to weld it from both sides due to lack of weld penetration, you just doubled the amount of heat applied, and thus the amount of shrinking in the area. You also see my second mistake here, the patch was made slightly small which left a gap between the panels on the vertical weld. It's a good practice to fit up your panels with no gap at all, as you have less chance of panel movement or pulling, and with that less chance of losing panel crown from the panels pulling together (especially prone in a horizontal weld)

http://i5.photobucket.com/albums/y167/rmccartney/1955%20Chevy%20Wagon%20Restoration%20Album%202/HPIM6339.jpg

Ground some welds off as I went, gets the excess out of the way for planishing the new welds.

http://i5.photobucket.com/albums/y167/rmccartney/1955%20Chevy%20Wagon%20Restoration%20Album%202/HPIM6342.jpg

http://i5.photobucket.com/albums/y167/rmccartney/1955%20Chevy%20Wagon%20Restoration%20Album%202/HPIM6345.jpg

http://i5.photobucket.com/albums/y167/rmccartney/1955%20Chevy%20Wagon%20Restoration%20Album%202/HPIM6346.jpg

The inner fender brace is pulled in snug and plug welded to the lower fender. The rest of the welds are filled in, skipping around as usual to minimize heat buildup, and then ground smooth.

http://i5.photobucket.com/albums/y167/rmccartney/1955%20Chevy%20Wagon%20Restoration%20Album%202/HPIM6348.jpg

http://i5.photobucket.com/albums/y167/rmccartney/1955%20Chevy%20Wagon%20Restoration%20Album%202/HPIM6350.jpg

http://i5.photobucket.com/albums/y167/rmccartney/1955%20Chevy%20Wagon%20Restoration%20Album%202/HPIM6352.jpg

JT56
12-28-2013, 09:07 PM
WOW Robert Great Work

chevynut
12-29-2013, 09:34 AM
I don't have a problem doing the patching, but the forming work you do is just incredible. And you do it with simple tools. Great writeups!