Automotive Bodywork: How to Repair Minor Rust to a Fender Edge

This chapter is about a real-world repair. Specifically, it details removing and replacing rusted metal in a lower-edge wheel well area in the front, right fender of a 1986 Jeep Comanche. This type of repair is called sectioning and is a frequent task in the real world of autobody metal projects.

 


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The cause of the rust damage? The plastic trim that covered it trapped water, salt, and dirt, holding them against the sheetmetal above it. As a result, the fender’s metal surface corroded, pitted, and rusted through in some places.

 

The first step in any rust repair job is to determine the extent of the damage. Picking and wire brushing are good ways to separate the sound metal from the weak metal.

The first step in any rust repair job is to determine the extent of the damage. Picking and wire brushing are good ways to separate the sound metal from the weak metal.

 

While fender replacement might be an economically preferable alternative to repairing this panel, this demonstration project shows what can be done to repair this kind of damage and how to do it. Another alternative, finding a used fender that is strong in this area and transplanting metal from it, might also be an attractive approach. However, finding such a fender probably would be difficult. The trim configuration that caused this damage would have caused it in identical fenders in most climates. There are always multiple valid approaches to any sheetmetal repair. The approach taken here is one of them.

 

The Approach

Two aspects of this job are uncommon: Traditional metal sectioning and finishing techniques are applied to a fairly modern panel. These techniques are usually reserved for panels in older vehicles because those panels are thicker and softer (contain less carbon) than is the case with this 1986 Jeep fender.

 

Hand or power wire brushing near the visible rust released loose paint, revealing additional weak areas lurking under the finish. This is essential knowledge to have before you begin repairs.

Hand or power wire brushing near the visible rust released loose paint, revealing additional weak areas lurking under the finish. This is essential knowledge to have before you begin repairs.

 

But because this panel will be fitted with modified trim that will not completely cover the repaired area, this area must have a fully finished appearance that was not part of its original configuration. That is why older and more time-consuming techniques were chosen to restore it. Many people believe that these older metal-working techniques cannot successfully be applied to modern sheetmetal because it is too thin and too hard. That is partially true. Modern, thin autobody panels do not weld as easily, or file as well, as the panel steels that were in use before the 1970s. The older techniques of sheetmetal work can be applied to modern panels, but only with great skill, time, patience, and often with somewhat compromised results. The approach, taken here, to this job requires intermediate to advanced skills.

 

The First Step: Evaluation

Cursory inspection of this fender revealed that the area was suspect for structural rust damage. Picking at it with a scriber, and hand brushing it with a carbon-steel-bristle brush, indicated that the metal could be punctured easily in this area. The same probing of other areas did not go through the metal.

Light abrasive blasting of the weak area and other suspected areas seemed to reveal the true extent of the damage. More probing and brushing followed.

 

Mild abrasive blasting poked holes through areas where the metal was weakest. This procedure also began cleaning the metal in the repair area for later steps, like welding, tinning, and filling.

Mild abrasive blasting poked holes through areas where the metal was weakest. This procedure also began cleaning the metal in the repair area for later steps, like welding, tinning, and filling.

 

Knowing the likely extent of the damage to this part of the fender, the next step was to mark it off so that a repair strategy could be formulated and followed. The marked area represents the shapes and sizes of the patch parts to be fabricated.

Knowing the likely extent of the damage to this part of the fender, the next step was to mark it off so that a repair strategy could be formulated and followed. The marked area represents the shapes and sizes of the patch parts to be fabricated.

 

Once the repair area was lightly blasted, some additional picking and hand wire brushing revealed the apparent extent of the rust damage.

Once the repair area was lightly blasted, some additional picking and hand wire brushing revealed the apparent extent of the rust damage.

 

This photo shows the boundaries of the metal that needs to be cut out of the panel, and replaced with new metal. Note the vertical index markings: These were used later to align the new, fabricated metal with the rest of the fender.

This photo shows the boundaries of the metal that needs to be cut out of the panel, and replaced with new metal. Note the vertical index markings: These were used later to align the new, fabricated metal with the rest of the fender.

 

When the full extent of the metal to be excised in this area was determined, it was marked for removal. It is always a good idea to remove metal beyond the actual suspect area, to ensure having sound steel to which to weld new metal.

Early in any sectioning project, where new metal will be fabricated to replace old metal, it is always advantageous to start an indexing system that will help you to accurately position the new metal. In this case, simple index marks were chalked onto the fender, for later transfer to templates and to new metal.

 

Removing the Bad Metal

There are many ways to remove metal from panels. Popular among them are: hand and power saws, nibblers, air or electric shears, grinding wheels, and plasma arc cutting. Different methods have different advantages and drawbacks in various situations. The object in this kind of cutting is to do as little collateral damage as possible, and to create as little distortion as is practical.

For this project, a very straight forward approach was favored. An entryway was ground into the fender with an air-driven muffler cutting wheel. Then a small reciprocating saw blade was inserted into the cut and moved along the cut line. This was done from both ends of the cut line.

Small air-driven reciprocating saws are handy for this kind of work. They are inexpensive, very maneuverable, and reasonably fast cutting. In this case, the entire removal operation took less than 10 minutes, producing a clean separation with no physical damage to the fender

Step 1:

7The first incision into the panel was made with an air-driven 3-inch muffler cutter. This allowed entry of the next tool, a small air-driven, reciprocating metal saw, used to cut the diseased metal out of the panel.

 
 

Step 2:

8This saw cuts more slowly than the grinder, but is easier to control and guide accurately. It cuts cleanly and without any damaging heat buildup, making it ideal for this job.

Step 3:

9The reciprocating saw can make turns that a grinding wheel cannot, but it causes some vibration and shake in the panel. While one hand is used to guide the saw along the chalked cut line, the other stabilizes one of the panel’s edges.

Step 4:

10The panel has the diseased metal removed. The excised material was in a high-stress area of the fender that included compound curves and strengthening creases, to deal with that stress. A good repair has to be structurally robust.

 
 

 

Planning and Modeling the Repair

With the bad metal removed, a sketch was made of the part needed to replace it. We decided to make the new part from two separate pieces and join them together, after each was tack welded into the fender. This approach was selected largely because each separate piece could be accurately and easily fabricated on a metal edge shrinker, a tool that was available for this job. Fabricating a patch from a single piece of metal would be more difficult, and would offer no particular structural or cosmetic advantage, beyond some bragging rights.

Good modeling is a critical step in sectioning work. It allows the metal worker to gauge and confirm the shapes and/or dimensions of new pieces to the ones that they replace. There are numerous ways to model any surface. The simplest is often the most useful. In this case, uninsulated copper electrical wire was used to model the format of the fender’s vertical edge. The more gradual curve of its horizontal (wheel arch) edge was transferred to a piece of insulated copper wire. Forming the uninsulated modeling wire to the fender’s vertical edge was easily accomplished by hand bending with a needle nose pliers. Uninsulated wire is best for accurately capturing small detail. Insulated wire bends naturally into long curves. The latter was used to capture the gradual curve of the horizontal fender arch in the sectioned area. The lateral indexing marks on the fender were transferred to it for later use.

Step 1:

11Planning a repair process, minutely, is one key to reducing the likelihood of unpleasant surprises. A sketch of what the repair patch will look like is a good first step.

 
 
 
 

Step 2:

12When bad metal is removed from a panel, it is critical to have some type of pattern or template to record its shape and contours, so that new metal can be formed accurately to replace it. This piece of 14-gauge electrical wire is easy to form and retains its shapes well.

 

Step 3:

13The wire is shaped, checked, and reshaped, until it fits the panel edge perfectly. Because the removed metal was too deformed to use as a pattern, an adjacent area was modeled. This worked because the feature being modeled is consistent and continuous.

 

Step 4:

14A lengthwise model was made from another piece of 14-gauge electrical wire, this time with its insulation on. This wire is marked with indexing from the fender that will later help to fit the panel patch accurately.

 

 

Cutting and Forming the Metal Patches

The tool chosen to perform the bulk of the forming work, an edge shrinker, is one of the most useful and versatile tools in the metal worker’s arsenal. It simply and easily shrinks metal on the edge of a piece by compacting it laterally, between two sets of jaws. In this case, a flat piece of 23-gauge body steel was cut to rough dimensions in a shear, and formed into roughly a right angle in a small sheetmetal brake. At this point, its format resembled that of a small piece of very light angle iron.

As the metal along one edge of the piece was compacted in the edge shrinker, the body of the piece began to curve. This curvature was constantly monitored and checked against the insulated wire template, until it was very close to the template’s shape. Then, it was indexed to the marks on the fender, and checked against the fender opening into which it later would be welded. After some fine tuning with the shrinker, a very good fit-up was attained.

Using the relevant index markings, the new piece was positioned in the fender opening and marked for approximate cut-off length. A little extra length was allowed for final fitting, and the piece was cut with aircraft shears. Slight deformation from the shearing was removed by lightly tapping the piece’s ends with a body hammer against an anvil. Then, the piece was ground to a final fit with a 41⁄2-inch electric disc grinder.

Step 1:

18This tool, a metal edge shrinker, is perfect for forming the long edge piece needed for this repair. As the surface between the jaws of the tool is laterally compressed the piece curves to accommodate the shrunken area, creating exactly the kind of curve needed for this repair part.

Step 2:

16As the new edge piece was formed, it was repeatedly checked against the wire template and modified accordingly. Although this edge shrinker has a foot control, using the hand lever gives the operator better control.

 

Step 3:

17As the repair piece approached the shape of the template its final shape it was checked against the cutout area, and indexing it was completed. It could not be fully and accurately indexed until it came close to its final shape.

Step 4:

18The last check of the repair piece against the cutout area revealed the need for slightly more curvature in the repair piece’s long section. This was applied.

 
 

Step 5:

19When the repair piece perfectly fit the contour of the cutout area, it was marked for lengthwise termination. The index markings were very helpful in accurately positioning it in the fender metal.

Step 6:

20Simple aircraft snips cut accurately enough to trim the long repair piece close to its final length dimension. Final length was adjusted by grinding. At this point, it was important to leave a little extra length, to allow for accurate, final fitting.

 

Step 7:

21The cutting operation slightly deformed the end edges of the long repair piece. These were easily straightened by gently tapping them against an anvil with a low-crown body hammer.

 

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Step 8:

22A small disc grinder was used for this piece’s final lengthwise trim. Because metal expands at welding temperatures, it is critical to trim repair pieces to provide expansion gaps between the thickness of a dime and a nickel to prevent their expansion from causing and locking in permanent panel distortions.

 
 

Step 9:

23Final fit for this piece was now checked and approved. In a repair like this, time invested in getting good fit-ups will be repaid many times over in time that will not have to be spent correcting a variety of problems.

Step 10:

24A piece of patch metal, cut to rough dimensions, was checked against the space that it will occupy between the panel and the long repair patch piece. Note the line on the short patch piece that represents the location of its center crease.

Step 11:

25The short repair piece’s center crease was formed in a finger brake. The angle of the bend exactly duplicated the crease in the fender flange to which it will be fitted.

 
 
 

Step 12:

26The copper wire template that was made of the fender edge shape was then used to check the bend in the repair piece. Rechecking and bending were performed until the match was perfect.

 

Step 13:

27With the patch piece bent to the correct angle, it was now roughly indexed to the long repair piece, and given preliminary marking for final dimensions. These dimensions could not be confirmed until the piece was near its correct, final contour.

Step 14:

28Once again our old friend, the edge shrinker, was the perfect tool for forming the contours needed in this part. The visible mark near the edge of the patch piece roughly indicates where it will be cut, but this may change as it is formed.

 
 
 

Step 15:

29Careful use of the shrinker yields a patch part that is remarkably close to the needed dimensions. Here, it is being marked for fitting between the fender and the long repair piece.

 
 
 
 

Step 16:

30The marked lines were then joined, freehand. This was the preliminary cut-out shape for the final patch, but extra metal was left on every edge for final fitting.

 
 
 
 
 
 

With the long patch piece that would form the edge of the fender completed, attention turned to forming the short patch piece that would replace the metal cut out of the flat part of the fender. After determining the rough dimensions for this part, a piece of body metal that was a little larger than the actual area to be formed was sheared from stock and checked against the opening into which it would fit. A line was drawn on the piece to show where it would need to be creased.

It was then bent in a finger brake to the angle indicated by the copper wire template, and marked on its edges for rough fitting into place, between the fender metal and the fabricated long edge piece.

Again, the edge shrinker was used to form it into the correct arc. Some fine adjustment to its surface curvature was made by hammering it lightly with a high-crown body hammer against a corrugated-cardboard backing. The piece was then positioned under the opening in the fender into which it would be fitted, and marked for final trimming.

 

Final Fitting

The big issue in final fitting is to fit the parts without excessive gaps, but not so tightly that the heat generated in welding them causes them to jam against and distort themselves and adjacent metal. The long piece in this fabrication presented few problems in fit-up. However, the short piece had the potential to distort its neighbors when welding heat was applied to it.

 

Final trimming and fitting were accomplished by grinding. Here, the inside edge of this patch piece, the one that will mate to the fender metal’s edge, is being slotted to allow bending this edge to the right contour and position.

Final trimming and fitting were accomplished by grinding. Here, the inside edge of this patch piece, the one that will mate to the fender metal’s edge, is being slotted to allow bending this edge to the right contour and position.

 

The short metal tabs were bent with a small pair of locking pliers. Note that this edge is formed in three dimensions. The slots that were cut into it allow for the expansion that occurs in welding, without excessive distortion.

The short metal tabs were bent with a small pair of locking pliers. Note that this edge is formed in three dimensions. The slots that were cut into it allow for the expansion that occurs in welding, without excessive distortion.

 

Actual final fitting of the short repair piece could not be completed until the long piece had been tack welded into place. That fitting is shown here, after one tack weld was made in one end of the short patch piece, to keep it in place.

Actual final fitting of the short repair piece could not be completed until the long piece had been tack welded into place. That fitting is shown here, after one tack weld was made in one end of the short patch piece, to keep it in place.

 

To avoid this, the edge of the piece that butted up against the side of the long piece was ground to give it some reliefs. This provided room for the metal there to expand under welding heat without creating damage. The reliefs were bent, individually, to create a straight edge for the welded piece. As welding progressed, the reliefs were welded over and closed.

 

Welding Considerations

The choice of welding technique and equipment to join the newly fabricated pieces to each other, and to the panel, was pretty obvious. The first decision was to make butt joints (edge-to-edge joints) where the fit-up involved butting edges. The only other choice would have been to make lap joints, with one edge over-lapping the other. These joints can be easier to make and to weld because they require less fit-up precision and they tolerate more heat without burning through. However, they are difficult to level, and can suffer severe attacks by corrosion. The joint between the two fabricated pieces is a right-angle joint, not a butt joint, and was welded in right-angle configuration.

To weld the butt joints and the right-angle joint, there are only three practical welding techniques available: oxy-acetylene torch, TIG, and MIG. As covered in Chapter 8, MIG (metal inert gas) welding is technically called GMAW (gas metal arc welding). TIG (tungsten inert gas) welding is more properly designated GTAW (gas tungsten arc welding).

 

It is usually impossible to make practice welds in the actual body panel materials that you will weld, but you can make them in materials of similar thickness. The welds shown here are in 23-gauge sheetmetal, the same thickness as that in the repair fender.

It is usually impossible to make practice welds in the actual body panel materials that you will weld, but you can make them in materials of similar thickness. The welds shown here are in 23-gauge sheetmetal, the same thickness as that in the repair fender.

 

The critical underside of the practice weld fully penetrates the metal. The object is to achieve that penetration, without excessive heat that burns through, or distorts, the panel and patches. Practice welds allow you to optimize welder settings and to perfect technique.

The critical underside of the practice weld fully penetrates the metal. The object is to achieve that penetration, without excessive heat that burns through, or distorts, the panel and patches. Practice welds allow you to optimize welder settings and to perfect technique.

 

The best test for penetration is to cut through a weld, and look at its cross-section. Such a cut is shown here, with the bead tops facing each other. The lacerations in the cuts are the marks left by the band saw that separated the pieces.

The best test for penetration is to cut through a weld, and look at its cross-section. Such a cut is shown here, with the bead tops facing each other. The lacerations in the cuts are the marks left by the band saw that separated the pieces.

 

The oxy-acetylene torch method was the traditional way of performing panel welding. In most autobody applications, it was replaced by MIG techniques and equipment during, and after, the 1970s. MIG welding requires less skill and experience than oxy-acetylene welding, and produces as good a weld in sheetmetal. It also produces much less distorting local heat. MIG welding equipment has become very inexpensive over the last 20 years.

TIG welding has been around since World War II, and is used for extremely fine work on materials like sheetmetal. However, TIG equipment is still quite expensive, and the skill required to use it is beyond that needed to do good work with MIG welding equipment. While TIG welding can be used at very low heats, with little distortion, it is also a very slow welding technique.

Following the above considerations, MIG welding was chosen for this job. Before performing the actual welds, several practice welds were completed on sample pieces of 23-gauge steel, the same thickness as the patch pieces that were fabricated, and the same thickness as the steel in the fender. The results of the practice welding were encouraging.

 

Cleaning, Positioning, Fixturing and Welding

The area of and near the site of attachment of the new metal to the panel was now disc sanded, so that good, clean metal would be available to weld. Cleaning weld areas generally makes it easier to see what is happening in areas adjacent to actual welds, when welding heat is applied. The long patch piece was secured in place with locking pliers, and a final visual check was made of its alignment with the fender edge. This piece was then tack welded into place, rechecked for final position, and seam welded to the fender. Our welder’s stitch timer function was used to switch the arc on and off for brief intervals during the welding, so that the bead was actually an accumulation of short welding pulses.

The timer device on our welder allows setting on and off times, individually, for the arc. The advantage of using this approach is that the short, interrupted welding intervals reduce the amount of heat buildup in the metal. This lessens the chance of burning through the metal, and helps to control excessive distortion near the weld seam.

Step 1:

37Prior to welding in the patch pieces, a disc sander is used to strip the weld area of most paint, contamination, and corrosion. Care was taken not to snag a metal edge with the sanding disc.

 
 

Step 2:

38A final check of lateral alignment was made for fitting of the long repair piece to the panel. Once welding starts, it is difficult, or impossible, to make any very major adjustments in the positions of the pieces.

 
 
 

Step 3:

39The long repair piece was tack welded into place with a MIG welding torch. The tacks held the pieces in place, while they were being joined into a continuous weld.

 
 

Step 4:

40Joining the tack welds between the long patch piece and the fender into a continuous weld is shown here. The welder’s stitch timer feature was used to pulse welding current on and off, between short weld segments. This somewhat mitigates heat buildup and distortion in areas near the weld bead.

 

Step 5:

41Now, the short repair patch was tacked into place. Note the panel gap between it, the fender, and the long patch piece metal. Magnets were used to hold this piece in place for tack welding.

 
 
 
 

Step 6:

42As welding progressed, panel alignment was checked, frequently. Here, a minor adjustment to the edge alignment of the short patch piece and the fender is made with gentle hammer tapping.

 
 
 
 
 
 
 

Step 7:

43After tacking, the short repair patch piece was welded into place, between the long patch piece and the fender. There was a problem: The metal near the fender seam was unexpectedly weak, and required re-welding to repair blow holes. This caused excessive heat distortion, generating a bulge in the fender metal.

 
 
 
 
 

Step 8:

44The welded-in patches are shown here. The over-welding and adjacent bulge are visible. The bulge will have to be dealt with later. If the repair had been extended 11⁄2 inches farther back into the fender metal, where it was sounder, the over-welding and bulge problems would not have occurred.

Step 9:

45This is the underside of the weld. It isn’t pretty, but it will never be seen. A little time spent leveling the area improves its appearance. Then, it will have to be protected from corrosion.

 

With the long patch piece completely secured to the panel, the short piece could now be attached to it and to the fender metal. After tack welding the short piece into place, one of its edges was tapped lightly into final alignment, and it was seam welded into place.

Unfortunately an evaluation mistake, made early in this project, led to a miscalculation that became evident when the short patch piece had been welded into place. The metal in the inner body of the fender that attaches to the short patch piece was weaker than had been thought. That resulted in blowing holes through it with the welder, while attaching it to the fender metal. The man making the weld somewhat instinctively over-welded the area to fill the holes, putting so much heat into the weld area that the metal bulged in the patch piece and adjacent fender.

 

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This bulge was caused by the heat expansion of an area bounded by unheated metal that restrained its further lateral movement. The only place for the overheated metal to go was into a bulge. It did so in the direction that the metal was already formed, causing the bulge. After everything cooled, the bulge remained.

This situation is typical of the kind of errors that sometimes occur in projects like this. Would it have been better to have not made this mistake? Of course it would. Should attention be turned to hand wringing and cursing providence over this situation? Of course not. Mistakes happen, and the only productive thing to do about them is to solve the problems that they bring and to move on, resolving to learn from them and to avoid them in the future. In this case, the correction was relatively simple.

 

Grinding the Weld Beads and Shrinking the Bulged Area

While the underside of this weld will not be visible in use, it is an issue of craftsmanship to give it a neat appearance. On fenders configured with their undersides more visible in this area, a more finished appearance would be mandatory. Here, the issue is one of choice—how far do you want to take the job? We opted for a neat but not-so-finished appearance. Our priorities were to leave the underside of the repair area clean and sound for coating with various anti-corrosion treatments like etching primer, resilient paint, and undercoating. It was important that the area be left smooth enough to accept paint uniformly, and that no features that could trap water and debris were left there to initiate or to encourage corrosion.

Next we attended to correcting the bulge that the welding had created in the short patch and fender metal. A couple of applications of shrinking technique resolved the bulge problem completely.

Step 1:

46Leveling was accomplished with a 4-inch air disc grinder. Its small size and considerable speed make it ideal for this job. It is easy to maneuver, and small enough to work around intricate features, without accidentally grinding them.

 
 

Step 2:

47After grinding, and some other abrasive stripping work, the underside of the welded area is ready for anti-corrosion treatments. Unseen areas, like this one, do not require much finishing and remain stronger if they are not leveled too extensively.

Step 3:

48Excessive heat in the over-welded area created a bulge in the patch and fender metal. This area was brought to cherry red with an oxy-acetylene torch, and hammered down in two operations that shrunk the metal, and relieved the bulge.

 
 
 

Step 4:

49While the metal in the bulged area was still hot, it was worked with a hammer-off-dolly technique to push the bulge farther down and to raise sunken areas around it. A low-crown hammer was used.

 
 
 

Step 5:

50A final step in the shrinking process was to quench the heated area with a wet sponge. This produced controlled shrinking action. Knowing exactly when and where to apply the quenching action requires some experience with this procedure.

 
 
 

The shrinking technique, in this case, involved heating the most distorted part of the bulge with an oxy-acetylene torch to a temperature between dull and cherry red. The area heated this way was a little larger than 1 inch in diameter. This caused further local bulging. The torch was then safely stowed, and the heated, bulged area was hammered down without any backing. This created an upset, literally a compacting of metal in a small area that exchanges lateral dimension for a locally thickened panel area.

The second shrinking operation was performed at a lower heat (dull red) and over a slightly wider area. This time, the hammering was done off-dolly, and the dolly rebound under the fender was used to raise some sunken metal around the bulge.

In this application, the metal in the formerly bulged area was quenched with a wet sponge to enhance and control the extent of the shrinking. The area was checked with a straightedge.

Measuring indicated that the bulge had been completely eliminated, and that the area now had the correct shape. Some distortion in the fender-edge repair patch metal was now removed by heating and hammering that area, gently, off-dolly.

Step 6:

51A check with a straightedge indicated that the shrinking operation was successful, and that the metal in the formerly bulged area was now within the range required for a good final result.

 

Step 7:

52A little bowing in one area of the outer edges of the long repair patch needed to be shrunk. That area was heated to dull red with an oxy-acetylene torch.

 

Step 8:

53After heating, the bowed area was hammered down, off-dolly, to upset the metal there. That means exchanging some of its lateral dimension for thickness, which amounts to compacting, or shrinking, its surface area.

 
 
 

 

Final Steps before Filling

The weld beads were now leveled to the fender by grinding, disc sanding, and filing them almost level with the surrounding metal. In the battle to level welds, it is fair to use any tool or device that helps do the job. In this case, we even used a rat-tail file and a die grinder.

After leveling the weld beads, the surface was inspected. No low or high spots were found that were beyond the range of modest filling and filing. A few low areas were raised slightly with a pick hammer, completing the metal finishing of the repair area.

The topside of the repair area was now completely cleaned and stripped to bare, healthy metal. All visible corrosion was removed. This operation was left until now because welding tends to create scale and debris that have to be removed before filling. Final cleaning after welding is the best approach, since removing every trace of contamination from the entire area before welding it would be a waste of time; it would just have to be done again.

The nylon disc-stripping wheel is a particularly useful tool for getting into the surface intricacies of metal and removing lightly pitted contamination from them. Following mechanical cleaning, the repair area was wiped down with solvent and blown dry. This was repeated until the wiping rags came up clean.

Step 1:

54Various grinding and disc sanding procedures were then applied to the surfaces in the repair area to clean, level, and prepare them for the next step: filling with body lead.

 
 
 
 
 
 

Step 2:

75Final leveling of some of the welds, in some areas, required a variety of approaches. Good, old fashioned filing with a rattail file is very useful for some of this work.

 
 

Step 3:

55A high-speed, air-driven, right-angle die grinder was particularly helpful for leveling some weld areas like the one shown here. This tool cuts quickly and accurately, and is easy to control.

 
 

Step 4:

56At this point, it was important to clean the entire repair area for the next steps, tinning and leading. Rotary and hand wire brushes, and other devices, sped this job, as did the grinder-mounted nylon/carbide wheel, shown here.

 
 
 

Step 5:

57Before moving on to the next step (tinning), the entire repair area was wiped down with solvent, and blown clean and dry. This procedure removed abrasive and chemical residues from the surface.

 
 
 
 

Tinning

We decided to fill the repair area with body lead to correct any low spots, and to allow us to file the surface to exactly the contours that would make the repair area indistinguishable from the rest of the fender. The first step was to tin the area to be leaded. It was pre-heated with an air-acetylene torch to about 300 degrees F. Tinning solution was then dripped onto it from a plastic squeeze container. At these temperatures, tinning solution chemically cleans base metal, preparing it to accept and adhere to tinning solder. As the tinning solution hit the panel metal, it sizzled on the hot surface, leaving a brownish film. That is the proper appearance for the application of this product.

Step 1:

58Tinning compound was dripped onto torch-heated metal in the repair area. The heat was supplied by an air-acetylene torch, and held to roughly 300 to 350 degrees F. The air-acetylene torch produces much milder heat than the oxy-acetylene torch, previously used for the shrinking operations.

Step 2:

59The tinning compound was brushed around on the hot metal with an acid brush, while more heat was applied to it. A visible, brown residue formed on the metal. This was a good indication that the tinning compound is doing its cleaning job.

Step 3:

60The 50/50 (tin/lead) solder was then unspooled from a coil and melted onto the surface. The torch was played over the area to keep the base metal hot enough for the solder to melt and flow onto it.

 

Step 4:

61While in a liquid state, the solder was spread on the metal surface with a rag. The tinning solder must fully cover the metal. However, rubbing it too hard with the rag may wipe it away completely, resulting in spotty bonding of the lead filler material.

 

Next, 50/50 (tin/lead) solder was uncoiled from a spool and run onto the metal’s surface, as the air-acetylene flame was played over it to keep it hot. After sufficient solder had been deposited on the entire area to be tinned, a rag was used to spread it evenly across the surface. During this operation, the air acetylene flame was played on the surface to keep it hot enough to maintain the solder in its liquid form.

A few spots that resisted the solder’s flow and adhesion received small additional applications of tinning flux. Then, the solder was brushed into them with a small stainless-steel-bristled brush. This worked, completing the tinning process. The whole area to be leaded was now covered with a uniform coating of tinning solder.

 

Applying the Lead Filler

The most outstanding characteristic of autobody lead the one that makes it ideal for filling depressions in metal work, while providing a medium for filing contours is that it is a metal applied to a metal. With correct application, the bond achieved with the metal substrate is unequalled by that of any other type of filler. However, paddling lead onto a properly tinned surface is about as difficult as making water run uphill.

Step 1:

62Lead from a 30/70 body solder bar was then stubbed onto the tinned surface. The end of the bar, and the metal around it, were heated until the lead started to soften. Then, a lead stub was twisted off the heated end of the bar, and onto the panel surface.

 
 

Step 2:

63The lead was softened to a plastic, bubble gum-like, consistency with the end of the torch flame, and spread on the repair area surface with a lubricated maple paddle. The lead application must be as even as possible, and generous enough to allow filing it to final contours.

64

 
 
 
 
 
 
 
 
 
 

Our first step was to stub a 30/70 (tin/lead) body solder bar onto the tinned surface. This was done by heating the end of the body solder bar, while playing the end of the air-acetylene flame over it and the tinned surface. The lead material has a plastic state at between 100 and 150 degrees F, depending on its composition. In this peanut-butter-like state, it can be twisted off in short stubs, onto the tinned surface.

After enough stubs were deposited, we spread them into a consistent layer of filler with a lubricated maple paddle, much as you might spread peanut butter with a small putty knife. While the filler looks somewhat rough, it was easy to file it into a smooth and accurate surface.

At this point, we killed the lead. That term describes neutralizing chemical residues from the flux used in tinning, and from the lubricant used to keep the maple leading paddle from sticking to the lead. While the killing process will be repeated on the panel after it is filed to its final format, as the last step in leading, it is also critical to do this before any filing is done. Otherwise, residues will be filed into the lead and it will be difficult, or impossible, to fully neutralize the finished surface.

Step 3:

T65hese two photographs show the repair area surface after the lead application was complete. The apparent roughness of the surface is not a problem, because body lead is a soft material and files easily into desired contours.

 
 

Step 4:

66The panel surface was wiped as clean as possible, and treated with metal conditioner. This step was repeated after filing and sanding were completed, but it is important to do it at this stage, to avoid filing contaminants into the filler, making them harder to remove later.

Step 5:

67After the metal conditioner had reacted with the metal in the repair area for a few minutes, it was wiped off. This step, and its repetition when the surface is completely contoured, prevents the loss of paint adhesion that can occur if these steps are omitted.

 
 

Shaping the Lead and Finishing the Job

Filing lead filler is not very different from grating and shaping plastic filler, except that different tools are used to do it and the shaping operation feels very different. We began shaping the lead with a bull-nose body file, and then switched to a flexible file holder and file to work on the flatter surfaces. Several different shaping tools were used.

During the filing process, the panel surface was constantly monitored, visually and by feel, to make sure that it was smooth and continuous. Some filing was solely in the lead filler material. In other areas of the repair, lead and steel panels were filed and blended into a continuous surface. Care was taken not to file too deeply in any area. Lead can be added to areas where it has been filed too deeply, but this is a tricky fix and care should be taken to avoid having to resort to it.

After filing was completed, the surface was sanded with 80-grit abrasive paper mounted on sanding boards. These boards place some-what soft rubber backings behind the abrasive paper, and tend to further average and blend the surfaces on which they are used. Paint sticks, wrapped in abrasive paper and without flexible backing, were used to sand some fine details into some areas of the lead and steel surfaces. Final sanding with 120-grit abrasive paper completed the surfacing phase of the job.

The entire repair area was again neutralized (killed) with metal conditioner, completing the repair.

Step 1:

68A variety of body files was used to achieve final, correct surface contours. This bull-nose file has a convex lateral format, and was perfect for removing material quickly and accurately in the concave area of this fender.

 

Step 2:

69This flexible file holder and file can be shaped to match desired surface contours. Most of the lead shaping and leveling was done with this setup. A good, sharp body file removes both lead filler and body metal, allowing the blending of both metals into a continuous surface.

Step 3:

70Other files, like this round bastard file, are useful for getting into tight areas, where flat files might tend to cut destructive channels and ridges into the lead filler and body metal. Filing requires great concentration, and involves both feel and visual inspection as it progresses.

 

Step 4:

72As the filled surface was filed, it was important to constantly feel surfaces and check for any depressions or raised spots. Proper filing technique employs files to blend raised spots into desired contours, and to avoid creating or lowering depressed areas.

 

Step 5:

73Filing was followed by board sanding. This board sander has a somewhat soft rubber backing under the abrasive paper. That helps to achieve continuous surfaces that have no unauthorized high or low spots or areas.

 
 
 

Step 6:

74Final sanding can be a finicky operation. Here, a paint stick was used to back abrasive paper. The surface warping of the stick is used to create a mildly concave or convex sanding tool, as required to contour and level the surface.

 
 
 
 

Written by Matt Joseph and Posted with Permission of CarTechBooks

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