the damage sequence first, and work
out the ridges and V-channels
it continued to deform the panel?
back to the first damage caused by
(mostly off-dolly) that represent
This is, in its essence, a cause-and-
the initial impact.
direct and, to a lesser degree, indirect
effect theory.
The reason for this approach is
damage. When this is done, most of
While this kind of investigation
that, when it is followed, the best
the rest of the indirect damage will
may sound complex and difficult, it
possible effort produces the best pos-
be released. The panel will then
really isn’t. There are only so many
sible result. Taking damage out in
return to its original, undamaged for-
possibilities for a sequence of events
the reverse order from how it was
mat, or close to it. And yes, it is as
that produces collision damage.
inflicted causes indirect damage to
simple as that.
Items like paint scrapes and pressure
spring back, mostly without apply-
Of course, a complex deforma-
embosses on metal provide excellent
ing unnecessary and possibly damag-
tion or a series of deformations in a
clues to the order in which damage
ing force to it. And, as they say on
panel look anything but simple.
occurred. With some experience, it
TV, “It really, really works!”
AUTOMOTIVE BODY WOR K AN D R UST R E PAI R
27
CHAPTE R 3
An Example of Simple Damage Repair
You can reduce complex damage,
dent was created. Removing this
either side of the crease, indicated by
that is, damage that may involve mul-
crease had to be done in a way that
lines C and D, which was bounded
tiple events and interrelated deforma-
did not upset or stretch the metal on
by undamaged metal.
tions of metal, to its simple
components by using the type of
analysis noted above. To make this
work, you need to know how to cor-
rect simple damage. Let’s illustrate this
process with a straightforward dent.
The dent in our example was
made by a single impact against the
hood. It cannot be determined
exactly how the damage occurred. It
may have resulted from an object
like a tree branch falling onto the
hood, or by the car being driven into
a low-hanging object. It clearly
occurred in one incident that
This simple dent in the hood of a
1
resulted in a mostly straight dent,
late 1940s Chrysler is about as
with a lateral crease at its center. This
basic as sheetmetal damage gets. It
is among the simplest of all dents,
happened in a single incident. Other
and one of the easiest to remove.
than pulling surrounding metal from
The first step in correcting this
the hood into the dent’s crease, there
damage was to determine its extent
was little secondary damage. Relieving
and boundaries. This was accom-
the center crease, without causing
plished by outlining the obvious
further deformation beyond the
damage area with chalk lines, fol-
damage boundaries, is the challenge here. As the crease is worked up,
lowed by lightly board sanding the
caution is needed to not upset the indirectly damaged metal.
damaged area, to more exactly define
those boundaries.
2
Then, it was possible to see
exactly
where
deformed
metal
Analysis
existed, and to outline the damage
of this
with precision. While the preceding
damage
steps may seem a bit fussy, note that
is simple.
they yielded some very useful infor-
An object
mation: The damage area was actu-
impacted
ally larger than the first chalk line
estimate indicated.
along line
The best approach to removing
A-B,
this damage was to work out the
creasing
Some board sanding revealed
3
crease in its center, the V-channel
it and pulling metal in from as far away
the exact limits of the out-of-
represented by line A-B, which was
as lines C and D. Returning the metal in
place metal. The damage area was
locking most of the metal in the dent
the crease A-B to its original position
larger than the first chalk estimate
out of place. Note that this was the
will release most of the indirect
indicated. Note that this is very heavy
first damage that occurred as the
damage between C and D.
sheetmetal, between 20- and 21-gauge.
28
AUTOMOTIVE BODY WOR K AN D R UST R E PAI R
T YP E S OF JOB S
With the board sanding
4
completed, the size and shape
The limits of the damage area
The underside of the damaged
5
6
of the damage area was confirmed.
were now redrawn in chalk. It
area looked like this. Crease A-B
This had already been determined by
was important to stabilize the metal
is evident, and you can see a hint of
feeling the metal but, in the planning
along lines C and D, as repair force
line D, near A. Knowing where things
stages of a repair, an accurate visual
was applied to crease A-B. This
are on the back side of this panel was
representation of damage is a more
prevented spreading the damage into
critical, because this was where most
useful than a tactile one.
new areas beyond C and D.
of the force to repair it was applied.
Here is a typical dolly position
From the back side, the
8
9
The deepest damage, near A,
on line C, near A, for
hammering along A-B looked
7
was worked up with a hammer-
hammering up crease A-B. The dolly
like this. Note the upright positioning
off-dolly technique. The dolly was
was used to prevent metal beyond
of the hood to provide good
alternated between supporting the
line C from bulging out, as A-B was
ergonomics for working on this
metal along lines C and D, as the
hammered up. It was critical to avoid
damage. There was plenty of room to
crease was worked up by hammering
upsetting the metal between A-B and
swing the hammer and hold the dolly,
it on the underside of the panel.
C as this was done.
and the access and position were
comfortable for the metal man.
After the worst of the damage
10 had been hammered up, it
remained to level the metal in the
damage area. A light shot bag was
used to support the metal, as
hammering continued. The shot bag
reduced the chance that an accidental
on-dolly hammer blow might stretch
the metal.
AUTOMOTIVE BODY WOR K AN D R UST R E PAI R
29
CHAPTE R 3
At this point, the damage area
11 was again board sanded to
More hammering on the crease
12
indicate progress, and to see what
A-B was done, with the area
The underside of the damage
13
remained to be done. This inspection
immediately adjacent to the crease
area was beginning to look
indicated that while much progress
supported off-dolly. Note that much of
much better. Very little of crease A-B
had been made raising the crease,
the indirect damage had come up to
or damage boundaries C and D
more metal in the crease area
level, and that the damage area had
remained visible. However, parts of
needed to be worked up.
been greatly reduced.
crease A-B stubbornly remained.
With
16
pick
hammering
completed
and its
results
confirmed
by feeling
By now, surface deviations in
The weapon of choice for
the surface,
14
15
the damage area had been
raising the remaining low spots
a disc
reduced to no more than a few
was a pick hammer. It can precisely
sander was
thousandths of an inch in depth. At
move small areas of metal in very
applied to the formerly damaged area
this point, feeling the damage was as
small increments, if you use it with
to level it and to indicate any low
useful as, or better than, seeing it.
concentration and patience.
spots that may remain.
To accomplish this, a mildly
bag, to back up the area where
crowned hammer was used to strike
lighter hammering was done.
the back of the V-channel with a slap-
At this point, most of the dam-
ping motion, while a flat dolly block
age has been removed, and a great
was held loosely against the metal
majority of the metal between lines
under the hammer. The dolly was off-
C and D has sprung back into place,
set to a location against the damage
as ridge A-B was driven up. Some
boundary, alternating between the
more hammer-off-dolly work, fol-
After a little contouring with a
sides of the dent, along lines C and D.
lowed by board sanding, revealed the
17 flexible body file and some
The dolly block prevented the ham-
progress that had been made. Some
more disc sanding, the repair area
mering force from inflicting further
depressed areas in the original crease
looked like this. The hood could now
deformation beyond lines C and D.
remained to be worked out.
be stripped, primed, and painted. No
After the major damage was
These low areas were raised with
filler was needed in the repair area,
hammered out, the dolly block was
a pick hammer. This procedure
because the metal was now level.
replaced with a small, handheld shot
involves lightly tapping them up,
30
AUTOMOTIVE BODY WOR K AN D R UST R E PAI R
T YP E S OF JOB S
raising the depressed metal a few
thousandths of an inch. Never get
wild with a pick hammer because that
will make a terrible, pocked mess of
your work. Feel depressed areas with
your fingertips, and raise them with a
gentle touch with your pick hammer.
The repair area was then disc sanded
to indicate remaining low spots, and
filed to level it.
Probing with an awl is a good
You can abrasively blast sheetmetal
Several of the previous steps
diagnostic technique. Delicate
without damaging it, if you use
(hammering-off-dolly, pick hammer-
abrasive blasting also helps to reveal
combinations of low blast pressures,
ing, and filing) were repeated until
weak and potentially perforated
shallow nozzle angles, long nozzle-to-
the panel was level. The job took
metal. Areas like this wire-edged
work distances, and abrasive-rich
about 40 minutes, and resulted in a
hood section are vulnerable to rust
air/abrasive mixtures. Without taking
surface that required no application
because they can trap moisture.
these precautions, you can badly
of filler material before it was painted.
warp sheetmetal.
This example of the removal of a
from an original panel, but you also
simple dent illustrates the main do not want to fail to go far enough
silicon carbide, and aluminum oxide,
features of this work. The damage
to remove all of the diseased metal
it takes a very light application of
was analyzed to determine how it
from a repair area.
these blasting media to avoid deform-
had occurred, and removed in the
Cleaning and probing a suspected
ing and damaging a panel. That kind
reverse order of its occurrence. Care
rust area with a pick should reveal its
of restraint involves exercising terrific
was taken to use as little force as pos-
extent. Abrasive blasting helps to
skill and judgment, but abrasive blast-
sible during the repair. Removal of
expose the extent of damage, but runs
ing can provide excellent cleaning.
the main V-channel was accom-
the risk of warping the panel. While it
Glass bead blasting media should
plished in ways that minimized any
is possible to clean metal for inspec-
never be used on body panels because
possible stretching or upsetting of the
tion with blast media like silica sand,
this stretches the side of the panel to
metal, and that stabilized the edges
of the damage area to avoid causing
additional injury beyond them.
Of course all of this takes prac-
tice, and requires a feel for the metal
and for what it is doing as you work
on it. These processes are the basic
ones used to remove dents. The prin-
cipl
es behind them apply to all
sheetmetal operations, including
fabrications.
Small Rust Repairs
Repairing small rust-outs is one
of the most common jobs in auto-
body metal work. The first step is to
determine the extent of the damage.
Don’t attempt to weld shut porosities and small holes on visible outer body
This requires judgment: You do not
metal. This approach is shown here, on a floor pan. It works because there are
want to remove serviceable metal
few holes, and the metal can be protected from further attack by corrosion.
AUTOMOTIVE BODY WOR K AN D R UST R E PAI R
31
CHAPTE R 3
This paper pattern was used to check
a complex shape: the top of a 1941
Willys fender that required sectioning.
By cutting flaps into the paper, a
three-dimensional pattern of the
There is no option here. The large area of this panel, outlined in tape, has to
fender top was formed.
be replaced with new metal. Trying to repair it would be a violation of the law
of diminishing returns.
which it is applied, and causes
metal that you need. You may be
warping. Blast processes that use
able to buy a panel containing the
media like soda and plastic bead—
section that you need from an origi-
known as soda blasting and PMB,
nal equipment manufacturer (OEM),
respectively—clean metal without
or from an aftermarket supplier. You
warping it, but not as thoroughly as
may have to find it as a salvage
harder blast media. Other processes
panel. Failing that, you may have to
that can accomplish good cleaning
modify a similar panel, or fabricate
are dip stripping in heated chemi-
one from scratch. In that case, you
cal baths that employ electrolysis,
should choose sheetmetal stock that
and the application of various abra-
is similar to the material that you are
sive wheels.
repairing in type and thickness. It
Once the extent of rust damage
should also be material that you can
is revealed, a repair strategy and
form easily, but that holds its shape
repair material can be selected. In
after it is formed.
some cases, welding shut small
If you have to form the section
A contour template was created for
defects (like pinholes) suffices, par-
that you need from sheet stock, or to
the fender top. It was drawn on paper,
ticularly if they are not in highly vis-
modify it from an existing formed
using a set of standard body curves