ible areas of panels, and if there are
piece, you need some method of pat-
(the blue plastic pieces). Then, a
not too many of them. In other
terning the original area, so that
paper template was transferred to
cases, replacement of large sections
your section or patch conforms to it.
cardboard. The cardboard template
of panels may be required. These are
There are many methods of pattern-
was used to check progress, as the
judgment calls that depend largely
ing sheetmetal in three dimensions;
fender top was being formed.
on your skills and resources, and on
some are very elaborate, while others
what level of results you are seeking.
are quite simple. Different situations
There are many methods of cut-
If you opt to replace part of a
may mandate using specific pattern-
ting out metal that will be replaced.
panel, known as sectioning, there are
ing techniques. In general, the sim-
(The use of these tools, and forming
several possibilities for securing the
plest techniques are often the best.
patch panels, are discussed later.)
32
AUTOMOTIVE BODY WOR K AN D R UST R E PAI R
T YP E S OF JOB S
Patterning and Forming a Small Rust Repair Patch
These photos illustrate a very simple electrical wire. This wire is easy to hand
In the final stages of the patterning
method of patterning a small rust
bend, and holds its shape wel , when used
operation, the pattern was held to the panel
patch for a decklid. It was damaged by
as a pattern to check the progress of the
on one side with a magnet, while fine adjust-
rust that formed in an area between the
sheetmetal patch panel formed from it. The
ments were made to the pattern grid.
metal skin and the supporting structure
first step was to bend it by hand, to bring the
A wooden stick was used to help
behind it. The rust area was outlined, and
pattern grid to the shape of the metal that
form the copper-wire grid against the
a slightly larger area was marked for the
the patch panel would replace. The pattern
decklid surface, until it conformed per-
patch.
grid was repeatedly checked against the
fectly to that surface, giving a faithful
A patch pattern template was formed
original panel as it was formed to it.
impression of the metal under it.
from a soldered grid of number-12 copper
The patterning technique
After each modification to the
2
3
The red felt-tip-marker line
used to model the metal that
pattern grid, it was checked
1
indicates the metal that had
was removed started by soldering
against the metal that it was being
to be cut out to make this rust
number-12 copper electrical wire
formed to model. This process took
repair. Access problems with
into a grid, roughly the size of the
several repeated steps, but each
supporting structure made cutting
metal to be cut out. The grid was
one brought the pattern grid closer
out the area bounded by the white
then formed by hand to conform to
to the panel’s contours.
lines a better strategy than just
the panel.
cutting out the weak metal.
As the grid became closer to
One corner of the grid that
4
5
the panel’s shape, a strong
resisted forming was bent
magnet was used to hold one of its
with the handle of a wire brush.
After a few minutes, the wire-
6
edges against the panel, so that
More pressure could be exerted
pattern grid exactly modeled
both hands could be used to refine
with the wooden handle than would
the surface. It was now a nearly
its shape, and to reveal areas that
be possible with bare hands.
perfect template for checking the
needed further forming.
new metal that would be formed.
AUTOMOTIVE BODY WOR K AN D R UST R E PAI R
33
CHAPTE R 3
This scissors-like pair of pneumatic
This is the panel patch that that was
A leather bag filled with lead or steel
metal shears is one of the more
modeled earlier. Modern planishing
shot and a plastic mallet can do
unusual devices that can be used to
hammers had origin in old, light-duty
wonders forming contours in
cut sheetmetal. It works surprisingly
body shop power hammers used to
sheetmetal. Smaller shot bags are
well, if you can get the access room
smooth large panels. They are useful
shown to the left of the one that is
to maneuver it.
for stretching and forming metal.
being used here.
The forming technique chosen to
make a repair patch depends on the
type of surface configuration that is
required. Many fabrications for rust-
repair patches employ relatively simple
methods.
Small Patch Piece
Welding Methods
There are three common meth-
ods for welding in small panel
patches: oxy-acetylene, MIG weld-
This blacksmith’s mushroom anvil, used with a medium-crown body hammer,
ing, and TIG welding.
allows very controlled forming of metal by stretching and shaping it.
Oxy-acetylene, or torch welding,
was once the dominant method for
performing this work. It produced
good results, but required consider-
able skill, and produced enough heat
around the welds made with this
method to badly distort the sur-
rounding metal. Correcting this dis-
tortion took considerable time and
effort. The same was true of arc weld-
ing, a process that also was once used
on sheetmetal, but that had tremen-
dous drawbacks in terms of the skill
required to perform it and the distor-
tion that it inflicted on panels.
This old tire-patching support device makes an excellent anvil for the shape
In the 1970s, metal inert gas
that is being formed on it. Sometimes you can innovate with the tools that you
(MIG) welding began to replace torch
use to form body metal.
welding in body shops. MIG is a form
34
AUTOMOTIVE BODY WOR K AN D R UST R E PAI R
T YP E S OF JOB S
TIG welding requires expensive
equipment and can be difficult to learn,
but it creates terrifically strong joints
with minimal heat distortion. When
quality is paramount, TIG is the way to
join sheetmetal panels or pieces.
Oxy-acetylene torch welding was the original method of joining sheetmetal
panels. It produces satisfactory welds, but requires a high level of skill. Note
that the welding rod is used to shield the weld puddle from the torch’s most
intense heat.
shops. Basically, this method feeds a
continuous electrode, or wire, into
the weld puddle, while shielding the
From top to bottom are a butt seam,
weld area from high temperature oxi-
lap seam, and offset lap seam. If
dation with a neutral gas that flows
properly made, butt seams are best
through the welding handle nozzle,
for appearance and durability. It
blanketing the weld area until it can
takes some practice to make this
cool a bit.
joint but once you master it, you will
When the electrode wire strikes
be glad that you did.
the welding target, it creates a short
circuit that heats and melts the wire
upside, TIG welding produces the
into the base metal. This creates and
best welds and the least distortion of
sustains a weld puddle. The heat
any welding method. Its advantages
melts off the end of the wire and
of quality are beyond dispute. How-
breaks the short circuit, but the wire
ever, it requires considerable skill to
re-feeds into the weld, recreating the
perform, and TIG equipment is very
This MIG welding unit is typical of the
short circuit, and repeating the cycle.
expensive. It is also a slow welding
high-quality modern welders that make
Another name for this phase of the
process, as such things go, but TIG
it easy to do excellent panel attachment
MIG welding process is short arc
should be considered if ultimate
work, with very little heat distortion
welding, a term that describes the
welding quality is your goal.
compared older techniques like oxy-
actual cycle of the process.
In addition to choosing a welding
acetylene torch and stick arc welding.
Today, MIG welders are compact,
process, it is necessary to decide what
relatively inexpensive, and highly
type of panel joint to use. Panel joints
of electric, or arc, welding. It requires
perfected. That is why MIG is by far
fall into three types: butt, lap, and off-
less skill than torch welding, and pro-
the most popular method of panel
set lap. Butt welded joints are by far
duces far less panel distortion. It has
welding in use today. However, tung-
the best. Lap welded and offset lap
become the standard method of weld-
sten inert gas (TIG) welding also has
welded joints may seem easier to
ing autobody sheet steel in repair
a distinct place in this work. On the
make, but are really more difficult. A
AUTOMOTIVE BODY WOR K AN D R UST R E PAI R
35
CHAPTE R 3
level of detail, and that has sufficient
accuracy for what you are fabricating.
It should also be a technique with
which you are comfortable, and in
which you have confidence.
Materials used to make patch
pieces should be similar to the metal
that will surround them. This is
absolutely necessary in the case of
large patch pieces or panels. If a
These panel-edge offsetters create
piece that is being cut out and
Holding patch pieces temporarily in
offsets in the edges of sheetmetal for
replaced is 20-gauge metal, the
place with magnets for tack welding
lap welding. The one on top is air-
replacement piece should match it in
works very well for most shapes and
over-hydraulic; the one on the bottom
thickness. Sheetmetal described as
configurations. This piece had a
runs off an air-driven zip gun.
1018 and 1020 cold roll is about
tendency to tilt out of position, so
right for most forming operations
several magnets were used to secure it.
properly fitted butt joint has a fin-
used to create small patches and
ished look on both sides; something
larger panel sections. These steels are
metal clips, and Clecos are among
that is critical when the underside of a
also very suitable for welding.
the most favored devices used to
repair patch may be visible. Also it
Patch pieces and panels can be
hold these panels in place prior to
doesn’t reveal its attachment point as
positioned for welding in many
tack welding, and for welding them
it ages and is subjected to flexing and
ways. Locking pliers, magnets, sheet-
into final position.
vibration. Lap welded and offset lap
welded joints have a tendency to reap-
pear in sheetmetal surfaces as they
age, because the metal in them is dou-
ble thickness and behaves differently
than a consistent butt welded area.
Large section patches, like the
rusted-out bottoms of doors, present
except that they have to integrate
and look good in longer runs of
metal and, therefore, must fit into
larger curves and sweeps. This means
that they can be more difficult to get
right than small patches, even
though the considerations in fitting
them are similar to those for small
area patches.
Patterning and forming small
patch pieces is covered in more detail
in Chapters 5 and 12. Similar tech-
niques are used to form large patch
panels. Many different approaches to
Here are several devices and their installation tools for holding sheetmetal
patterning yield good results. You
pieces in place for tack welding. On the left: Clecos and Cleco edge holders.
should choose a patterning tech-
To their right: wing nut clips; compression edge clips; and on the far right,
nique that captures an appropriate
locking pliers. The top set has self-aligning swivel ends, a handy feature.
36
AUTOMOTIVE BODY WOR K AN D R UST R E PAI R
C H A P T E R 4
CLEANING, MODELING AND CUTTING
This chapter discusses the best
ways to clean, model, and cut sheet-
metal. These tasks are basic to all
panel sectioning jobs, and to many
fabrication projects. They are crucial
to everything that follows.
Preparing and Cleaning
Sheetmetal
Whether panel steel is old or
new, it is important to clean it to bare
metal at a fairly early stage of work-
ing with it. You can begin working
with dirty steel; and
sometimes it’s
advantageous to start work with steel
panels that still have old paint and/or
rust on them. Filing and sanding
these things off can help to indicate
surface deformations and damage. In
Cleaning metal can be one of the most important and time-consuming
a sense, these defects can become a
preparations in metal work. If it is done properly, it should reveal the true condition
kind of guide coat as work progresses.
of the sheetmetal, and indicate repair measures that may need to be pursued.
However, by the time you get to
hammer forming or welding panel
should be removed with an appropri-
Neither of these practices is recom-
materials, you should be thinking
ate solvent before new metal is
mended or even acceptable today.
about cleaning them. This is also true
welded or passed on for painting.
Paint can be removed with any
of new metal that is used in repair
There are many ways to clean
of several solvents designed for that
and for fabrication projects. While
sheetmetal. Body shop practice was
purpose. These vary in speed and
new steel-panel material looks clean,
once to treat it with muriatic acid
thoroughness. If you have to strip
it is usually coated with preservative
(hydrochloric acid/HCL), or to use a
paint from a large panel, like a door
oil before it is shipped. This oil
blow torch to burn off old paint. or hood, general-purpose paint
AUTOMOTIVE BODY WOR K AN D R UST R E PAI R
37
CHAPTE R 4
Twisted wire cup brushes, like this
one, are good for digging into rust
pits in sheetmetal. It is important to
change them often because their
wires bend and their ends dull quickly.
Chemical paint stripper is one way to remove old paint. This is a general-
purpose product. Aircraft stripper is a better bet for autobody panels. Muriatic
7- and 9-inch devices) have is that
acid and blow torches (on the right) were once used for paint removal. These
they indicate surface defects and fea-
were dangerous practices, and are now obsolete.
tures, while removing paint and rust.
Wire cup wheels are very good for dig-
sander is also an acceptable but slow
ging into rust pits but tend to dull and
way to remove paint. It has an advan-
bend quickly, losing much of their
tage over chemical means of paint
effectiveness.
removal: It also removes surface rust.