Automotive Bodywork and Rust Repair
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The last check of the repair
4
piece against the cut-out area
revealed the need for slightly more
As the repair piece approached the shape of the template—its final shape—
curvature in the repair piece’s long
3
it was checked against the cut-out area, and indexing it was completed. It
section. This was applied.
could not be fully and accurately indexed until it came close to its final shape.
Simple aircraft snips cut
6
accurately enough to trim the
When the repair piece perfectly fit the contour of the cut-out area, it was
long repair piece close to its final length
5
marked for lengthwise termination. The index markings were very
dimension. Final length was adjusted
helpful in accurately positioning it in the fender metal.
by grinding. At this point, it was
important to leave a little extra length,
to allow for accurate, final fitting.
A small disc grinder was used
8
for this piece’s final lengthwise
trim. Because metal expands at
The cutting operation slightly
welding temperatures, it is critical to
7
deformed the end edges of the
trim repair pieces to provide expansion
long repair piece. These were easily
gaps—between the thickness of a dime
straightened by gently tapping them
and a nickel—to prevent their
against an anvil with a low-crown
expansion from causing and locking in
body hammer.
permanent panel distortions.
Final fit for this piece was now
9
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.
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CHAPTE R 12
A piece of patch metal, cut to
10 rough dimensions, was checked
The copper wire template that
12
against the space that it will occupy
The short repair piece’s center
was made of the fender edge
11
between the panel and the long repair
crease was formed in a finger
shape was then used to check the
patch piece. Note the line on the short
brake. The angle of the bend exactly
bend in the repair piece. Rechecking
patch piece that represents the
duplicated the crease in the fender
and bending were performed until the
location of its center crease.
flange to which it will be fitted.
match was perfect.
With the patch piece bent to the
13 correct angle, it was now
roughly indexed to the long repair
piece, and given preliminary marking
for final dimensions. These dimensions
Once again our old friend, the
14
could not be confirmed until the piece
edge shrinker, was the perfect
Careful use of the shrinker yields
15
was near its correct, final contour.
tool for forming the contours needed
a patch part that is remarkably
in this part. The visible mark near the
close to the needed dimensions. Here,
shears. Slight deformation from the
edge of the patch piece roughly
it is being marked for fitting between
shearing was removed by lightly tap-
indicates where it will be cut, but this
the fender and the long repair piece.
ping the piece’s ends with a body
may change as it is formed.
hammer against an anvil. Then, the
piece was ground to a final fit with a
It was then bent in a finger brake
41⁄2-inch electric disc grinder.
to the angle indicated by the copper
With the long patch piece that
wire template, and marked on its
would form the edge of the fender
edges for rough fitting into place,
completed, attention turned to form-
between the fender metal and the
ing the short patch piece that would
fabricated long edge piece.
replace the metal cut out of the flat
Again, the edge shrinker was
part of the fender. After determining
used to form it into the correct arc.
the rough dimensions for this part, a
Some fine adjustment to its surface
piece of body metal that was a little
curvature was made by hammering it
larger than the actual area to be
lightly with a high-crown body ham-
formed was sheared from stock and
mer against a corrugated-cardboard
The marked lines were then
16
checked against the opening into
backing. The piece was then posi-
joined, freehand. This was the
which it would fit. A line was drawn
tioned under the opening in the
preliminary cut-out shape for the final
on the piece to show where it would
fender into which it would be fitted,
patch, but extra metal was left on
need to be creased.
and marked for final trimming.
every edge for final fitting.
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Final Fitting
The big issue in final fitting is to
fit the parts without excessive gaps,
but not so tightly that the heat gen-
erated 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 dis-
tort its neighbors when welding heat
was applied to it.
To avoid this, the edge of the piece
Final trimming and fitting were
that butted up against the side of the
accomplished by grinding. Here, the
The short metal tabs were bent with a
long piece was ground to give it some
inside edge of this patch piece, the
small pair of locking pliers. Note that
reliefs. This provided room for the
one that will mate to the fender
this edge is formed in three
metal there to expand under welding
metal’s edge, is being slotted to allow
dimensions. The slots that were cut into
heat without creating damage. The
bending this edge to the right contour
it allow for the expansion that occurs in
reliefs were bent, individually, to cre-
and position.
welding, without excessive distortion.
ate 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
Actual final fitting of the short repair piece could not be completed until the long
other choice would have been to
piece had been tack welded into place. That fitting is shown here, after one tack
make lap joints, with one edge over-
weld was made in one end of the short patch piece, to keep it in place.
lapping the other. These joints can
be easier to make and to weld
practical welding techniques avail-
replaced by MIG techniques and
because they require less fit-up preci-
able: oxy-acetylene torch, TIG, and
equipment during, and after, the
sion and they tolerate more heat
MIG. As covered in Chapter 8, MIG
1970s. MIG welding requires less
without burning through. However,
(metal inert gas) welding is technically
skill and experience than oxy-
they are difficult to level, and can
called GMAW (gas metal arc weld-
acetylene welding, and produces as
suffer severe attacks by corrosion.
ing). TIG (tungsten inert gas) weld-
good a weld in sheetmetal. It also
The joint between the two fabricated
ing is more properly designated
produces much less distorting local
pieces is a right-angle joint, not a
GTAW (gas tungsten arc welding).
heat. MIG welding equipment has
butt joint, and was welded in right-
The
oxy-acetylene
torch
become very inexpensive over the
angle configuration.
method was the traditional way of
last 20 years.
To weld the butt joints and the
performing panel welding. In most
TIG welding has been around
right-angle joint, there are only three
autobody
applications,
it
was
since World War II, and is used for
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The critical underside of the practice
It is usually impossible to make
weld fully penetrates the metal. The
practice welds in the actual body panel
object is to achieve that penetration,
materials that you will weld, but you
without excessive heat that burns
can make them in materials of similar
through, or distorts, the panel and
thickness. The welds shown here are in
patches. Practice welds allow you to
The best test for penetration is to cut
23-gauge sheetmetal, the same
optimize welder settings and to
through a weld, and look at its cross-
thickness as that in the repair fender.
perfect technique.
section. Such a cut is shown here,
with the bead tops facing each other.
extremely fine work on materials
tion, it is also a very slow welding
The lacerations in the cuts are the
like sheetmetal. However, TIG
technique.
marks left by the band saw that
equipment is still quite expensive,
Following the above considera-
separated the pieces.
and the skill required to use it is
tions, MIG welding was chosen for
beyond that needed to do good
this job. Before performing the
the patch pieces that were fabricated,
work with MIG welding equipment.
actual welds, several practice welds
and the same thickness as the steel in
While TIG welding can be used at
were completed on sample pieces of
the fender. The results of the practice
very low heats, with little distor-
23-gauge steel, the same thickness as
welding were encouraging.
Cleaning, Positioning, Fixturing and Welding
The area of and near the site of
The timer device on our welder
short, interrupted welding intervals
attachment of the new metal to the
allows setting on and off times, indi-
reduce the amount of heat buildup
panel was now disc sanded, so that
vidually, for the arc. The advantage
in the metal. This lessens the chance
good, clean metal would be available
of using this approach is that the
of burning through the metal, and
to weld. Cleaning weld areas gener-
ally makes it easier to see what is hap-
pening 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 align-
ment with the fender edge. This
piece was then tack welded into
place, rechecked for final position,
and seam welded to the fender. Our
Prior to welding in the patch
A final check of lateral alignment
1
2
welder’s stitch timer function was
pieces, a disc sander is used to
was made for fitting of the long
used to switch the arc on and off for
strip the weld area of most paint,
repair piece to the panel. Once welding
brief intervals during the welding, so
contamination, and corrosion. Care
starts, it is difficult, or impossible, to
that the bead was actually an accu-
was taken not to snag a metal edge
make any very major adjustments in
mulation of short welding pulses.
with the sanding disc.
the positions of the pieces.
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Joining the tack welds between
4
the long patch piece and the
fender into a continuous weld is
The long repair piece was tack welded into place with a MIG welding
shown here. The welder’s stitch timer
3
torch. The tacks held the pieces in place, while they were being joined
feature was used to pulse welding
into a continuous weld.
current on and off, between short
weld segments. This somewhat
mitigates heat buildup and distortion
in areas near the weld bead.
Now, the short repair patch was
5
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
As welding progressed, panel
6
for tack welding.
alignment was checked,
frequently. Here, a minor adjustment
After tacking, the short repair
7
> helps to control excessive distortion
to the edge alignment of the short
patch piece was welded into
near the weld seam.
patch piece and the fender is made
place, between the long patch piece
With the long patch piece com-
with gentle hammer tapping.
and the fender. There was a problem:
pletely secured to the panel, the
The metal near the fender seam was
short piece could now be attached to
led to a miscalculation that became
unexpectedly weak, and required re-
it and to the fender metal. After tack
evident when the short patch piece
welding to repair blow holes. This
welding the short piece into place,
had been welded into place. The
caused exces-sive heat distortion,
one of its edges was tapped lightly
metal in the inner body of the fender
generating a bulge in the fender metal.
into final alignment, and it was seam
that attaches to the short patch piece
welded into place.
was weaker than had been thought.
attaching it to the fender metal. The
Unfortunately
an
evaluation
That resulted in blowing holes
man making the weld somewhat
mistake, made early in this project,
through it with the welder, while
instinctively over-welded the area to
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CHAPTE R 12
fill the holes, putting so much heat
into the weld area that the metal
bulged in the patch piece and adja-
cent fender.
This bulge was caused by the heat
expansion of an area bounded by
unheated metal that restrained its fur-
ther lateral movement. The only place
for the overheated metal to go was
into a bulge. It did so in the direction
The welded-in patches are shown here. The over-welding and adjacent
8
that the metal was already formed,
bulge are visible. The bulge will have to be dealt with later. If the repair
causing the bulge. After everything
had been extended 11⁄2 inches farther back into the fender metal, where it was
cooled, the bulge remained.
sounder, the over-welding and bulge problems would not have occurred.
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 wring-
ing and cursing providence over this
situation? Of course not. Mistakes