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tech article '35 Chevy Master Coupe fender repair


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I'm currently working on a '35 Chevy Master coupe, restoring the sheetmetal to "like new" condition. The left front fender had suffered lots of damage over the years and due to several fatigue cracks, heavy rust pitting and thinned metal from pick and file gremlins, the only way to properly repair it was to replace these sections. This may end up being about a three part series by the time this fender is complete.

The first step in this process is to make the surface true and smooth. I had to do a little shrinking on the high spots to get those down, then skim coated the area to be replaced with body filler. The body filler is sanded smooth, just as if it were going to be prepped for primer. This prepares the surface for making the pattern.

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To make the pattern, I use a layer of vinyl sign makers transfer tape, followed by a layer or two of fiberglass reinforced strapping tape. This will hold the shape (surface area) of the panel, but will do nothing for referencing the form (final arrangement) of the panel. The tape pattern captures the surface area of the panel so that as it is hammered and wheeled into shape, it can be used as a guide as to where the metal needs stretched or shrunk. Any place the pattern fits loose against the new panel, the metal must stretch to fill that void. If it fits tight in a given area, that area either needs to shrink, or the surrounding area will need stretched. When the proper amount of surface area has been introduced into the new panel by means of stretching and shrinking the metal, the pattern will fit like a glove, with no voids anywhere. The entire surface of the pattern will fit tightly to the new panel. The holes you see in the pattern serve two purposes. One is to make sure the panel rests in the same exact spot each time. To ensure this, a marker is used to mark through those holes for aligning the pattern properly each time. The other reason will be discussed in a moment.

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Once the surface area is correct, contour gages are used to place the new panel into the proper arrangement (form) Since we are no longer stretching or shrinking the metal, we can manifulate it by hand to get it in to this proper arrangement. The surface area (shape) is already present, so the metal moves pretty easily by hand into the proper arrangement to fit the existing part. The contour gages are made of 3/4" strips of metal, bent in a shrinker/stretcher outfit to match the contour of the panel being copied. To make sure I have these placed in the proper area to compare the new panel to the original, I mark the flexible shape pattern with straight lines where I want the countour gage to rest. Along these straight lines, I punch a series of holes so that I can align the pattern during the shaping process and also to use as a guide as to where the gages will be placed on the new panel.

If this panel were to be made more than once, a buck would be the way to go for fitting the new panel to each time. I would still use the flexible shape pattern, but would not need the contour gages, as the buck would eliminate the need for them. In this case, the contour gages act as the buck. One other point of interest in doing it this way, is that if this fender has been so bad that I could not make a pattern from it, I could easily have used the right fender to make the flexible shape pattern and contour gages from and just reversed the pattern.

You will notice that I use a numeric system to keep track of where the gages are placed to correspond with the pattern.

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Another important feature of the flexible shape pattern is that it can easily be used for laying out feature lines, etc., such as the bead that goes around the wheel opening of this fender. The pattern is simply taped into position and fineline tape works well to follow the edge of the pattern for a guide when running it through the tipping wheel or bead roller. The flexible shape pattern is removed prior to the tipping operation though, of course.

I'll try getting a picture of the tipping procedure for the next installment. Here the panel is lying in position. I haven't cut out the old metal yet, so it's just sitting there on top of it.

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Next time, I'll discuss fitting and welding issues, as well as dealing with post weld warpage and planishing.

Randy Ferguson

Ferguson Coachbuilding

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