moved most of the metal to level. A little
It remained to disc sand the entire
both types. There are also specialty
more picking and filing followed. This
area around and between the dents with an
files, like laterally concave and con-
revealed that the damage was completely
80-grit disc, and then to scuff the area with
vex, and lengthwise convex (“banjo”)
removed, and that the panel crown around
an 80-grit DA random-orbital sander. This
files. As well, there are specialty file
and between the two dents was consis-
achieved a surface that was smooth, and
holders for particular jobs. The most
tent and correct.
that had good tooth for primer adhesion.
useful general-purpose holder is a
flexible metal rig that allows you to
custom contour files by adjusting the
holder. This is important for working
with different crowns, and in some
situations where access is a problem.
The instructions for using body
files are based on time-tested methods
of filing, and are designed to optimize
both revealing depressions in metal,
After the first picking
and leveling it. The first rule is to
5
operations, the repair area
The repair area was now
always file toward the flattest crown in
6
was filed with a flat body file
smoothed with a disc sander,
a panel. This reveals low spots as voids
mounted in a flexible holder. Most
loaded with 80-grit paper. This
in filed metal, while preventing the file
of the metal came level at this point,
removed most of the scratches
from skipping over features of the
but some additional picking and
resulting from the paint removal
panel, like crown changes, as might
re-filing were required to completely
and filing operations. Note the
happen if you fail to file toward low-
remove the dents, and to give the
almost flat position of the sanding
crown areas.
panel a consistent contour.
disc for this procedure.
Your filing stroke should use as
much of your file’s length, in contact
with metal, as is practical. As you
file, there are two motions that
should be used, beyond pushing the
file forward and away from you.
The first is to slide it sideways,
about 15 to 20 percent of the dis-
tance that you push it forward. This
must be done smoothly, or gouging
may occur. If you see tooth gouges in
The filed panel looked like
the metal, you are doing something
7
this. Note the filing scratches
After a scuff sanding with
wrong. The second motion amounts
8
in the repair area. This repair
80-grit paper in a dual action
to a subtle shift of force. It is to rock
required so little filing that there
(DA) orbital sander, the repaired
the file from its front (toe) to its back
was question whether the repaired
surface was smooth and had good
(heal) as you push it away from you,
panel had any badly thinned areas
tooth to hold primer. The
forward and sideways.
or spots.
completed repair is shown here.
Since, as a child, you doubtless
mastered the trick of rubbing your
tummy in a circular motion with one
AUTOMOTIVE BODY WOR K AN D R UST R E PAI R
65
CHAPTE R 7
hand, while patting the top of your
made because sharp looks purposeful
side with their fingers, until it is in
head with the other hand, the filing
and sexy. After all, stiletto heels and
the right place. Another locating
motions that I describe here should
sharp
features
of
the
human
technique is to follow the hammer
come to you as, well, kid’s stuff. If
anatomy are said to convey sexual
under or behind the panel and sense
they don’t, hours of practice certainly
appeal and power. However, in pick
where it is located in relation to the
helps to fill any gaps. This combined
hammers, very sharp items are more
side that you can see. This works for
filing motion is important and well
useful for assault than for serious
locating where to hit metal up. How-
worth mastering. Once you do, it
body work. If very spiked pick-ham-
ever, it leaves the problem of hitting
should quickly become natural.
mers have any good application, it is
exactly the spot that you have identi-
The sideways file shift should be
for very fine work; and then, only in
fied. You might be amazed at how
alternated from one side to the other.
the hands of very highly skilled and
lost that spot can become, between
Say that you start by filing forward,
seasoned metal workers.
nesting a hammer on it, and then
and shifting your file to the left. You
That first problem, locating the
swinging the hammer away from it
may repeat this stroke a few times.
place to raise metal, amounts to
and then toward it again. Several
Then, you should begin filing the
translating where you know a low
short, light strokes work best for pick-
same area to the right, from the point
spot is from the side of the metal that
ing. A short stroke presents less
where your earlier file strokes ended.
you can see, to the one that you can-
chance of missing your spot. And if
In this way, you cover an area of
not. There are body workers who do
you do miss it, a short stroke does less
maybe 1 foot x 3 to 5 inches, always
this by hitting tentatively with their
damage than a more powerful one.
filing toward areas of lower crown.
pick hammers from the backs of pan-
After you gain pick hammer
els, and sensing the hit on the other
experience, you will be able to find
The Art of Pick Hammering
Here is one of those confidence
builders. The first time that you try to
use a pick hammer, you will, almost
certainly, make a complete mess of it.
I know that I did. This is because
once their function is explained, peo-
ple expect pick hammers to be mira-
cle tools that naturally find low
spots, and apply just enough hit to
raise them to the perfect level for fin-
ish filing. Sadly, to date, no such pick
hammer has been invented.
The first problem is that without
some experience in the matter, it is
frustratingly difficult to hit exactly
the right spot with a pick hammer.
That spot is usually on the other side
of the panel from the one at which
you are looking, so you are hammer-
ing toward yourself. The second
problem is that people tend to
choose pick hammers that are far too
This pick-hammer assortment has just about every device that you will ever
sharp for what they are trying to
need for picking work. The sharp, pointed one (top) has limited application,
accomplish. I suppose that these pre-
mostly for very fine tuning operations. The bottom three picks cover most
dictably bad hammer choices are
work to raise small low spots.
66
AUTOMOTIVE BODY WOR K AN D R UST R E PAI R
M ETAL F I N I S H I NG
the right spot on the other side of a
panel fairly quickly, as a result of
increasing your hand/eye coordina-
tion. It is still a good idea to give
the identified spot a light tap and
feel its location through the metal,
to confirm that it is correct. You
will learn to see the metal rising
each time that you hit it with your
pick hammer. This allows you to
make small adjustments in your
hammering position, as you moni-
tor your results from the other side
of the panel. Always remember that
you are trying to move metal just a
few thousandths of an inch, and
that you can correct some inaccura-
cies in your picking in the filing
stage that follows it. Many small,
incremental hammer strokes do the
job far better than a few heavy
ones, and involve much less risk to
the panel.
Left to right: 9- and 7-inch electric disc sanders. Right: a 7-inch pneumatic disc
Once you get the hang of picking
sander. Electric sanders are preferred for metal finishing, because they have
metal up, it is easy to get carried
more torque. Note the warped disc on the middle sander. It will cause
away, and to try to raise it to
chattering and skips if its disc is not changed for a flat one.
Himalayan heights. This is unneces-
sary and it is destructive. To level
The Disc Sanding Alternative
body work is done with 7-inch units,
metal, you need to pick up low spots
with either rubber or fiber backings
to a point just above panel height.
After you have mastered the tech-
behind the abrasive discs. When disc
This allows you to file it perfectly
niques of using body files and pick
sanders are used for paint removal,
level. If you raise metal beyond that
hammers to level metal, the brave
an open-coat abrasive disc is pre-
point, when you file, you need to
new world of disc sanding awaits
ferred. When they are employed
remove more metal than is necessary
your discovery. Disc sanding offers an
in metal finishing, closed-coat,
to get things level. Always stop pick-
alternative to body filing, but comes
resin-bonded abrasives are best. The
ing just after you achieve level, and
with several cautions and warnings.
36- and 50-grit sizes are appropriate
let your body file or sander do the
Disc sanding tends to be much faster
for metal finishing with a disc sander,
rest. You make this determination by
than body filing and, for that reason,
while 50-, 60-, and 80-grit sizes have
running your finger tips over the
it can damage a panel much faster
applications for the final smoothing
spot that you are picking. It is a good
than filing it. The degree of difficulty
of metal, after it is leveled.
idea to put a smooth, clean rag or tis-
in using a body file or disc sander is
The first phase of using a disc
sue under your finger tips when you
about the same. Which technique
sander for metal finishing is the dis-
do this. That prevents the oils and
you choose is largely a matter of per-
covery phase. It involves disc sand-
moisture on them from making your
sonal preference. Many body metal
ing metal surfaces so that the sander
fingers grip, drag, or grab on the
workers use both techniques, each in
skips over depressed areas in a way
metal as you feel it, and gives you a
specific situations or in sequence.
that reveals their presence.
much better sense of the topography
Disc sanders come in various
Proper disc sanding technique,
of what you are feeling.
powers, speeds, and disc sizes. Most
in the discovery phase of the
AUTOMOTIVE BODY WOR K AN D R UST R E PAI R
67
CHAPTE R 7
Disc
sanding
for
discovery
should leave a series of swirl marks,
or shiny paths. Any voids or dull
spots in these paths are low spots.
High spots may leave visible low
voids around them. However, if they
are not very high—not high enough
to need to be hammered down—
they will be ground off by the disc
sander as it passes over them,
thereby ceasing to be a problem.
sander and pick hammer is the same
as for a pick hammer and body file.
Sanding identifies low spots and
removes most high spots. Hammer-
ing, as necessary and preferably with
a low-crown hammer, drives down
the high spots that are not removed
by sanding. Hammering, usually with
a pick hammer, picks up low areas.
Occasionally, when low areas are rela-
The final procedure in metal finishing is to disc polish the metal with 50-, 60-,
tively large, they need to be driven up
or 80-grit abrasives. This gives it a sheen that makes it easy to spot dimen-
with a highly crowned hammer. As
sional deviations. I always dull that finish with a DA orbital sander, for better
with filing, the hammering and sand-
paint adhesion.
ing operations are repeated until the
panel is level and continuous. Also, as
operation, is to hold the abrasive disc
sander, as you reverse its direction,
with filing, disc sanding removes
against the metal with moderate
but that is clumsier than slightly lift-
material and cannot be repeated to
pressure, tilted about 15 degrees
ing it to reduce the pressure on its
the point of excessively reducing the
away from it, and toward you, so
contact edge. When travel resumes,
thickness of a panel.
that the sanding disc’s edge bends to
in t
he opposite direction from the
The 36- and/or 50-grit abrasives
contact and cut a narrow swath of
just completed stroke, the leading
used in the discovery and leveling
surface, say 1 to 11⁄4 inch wide. The
edge of the sander should be raised,
phases of disc sanding leave surfaces
sander is moved sideways, and held
just slightly, in the new direction of
that are too rough to complete the
mostly laterally flat to the panel,
travel, as it was before.
metal finishing phase of panel work,
with a very small amount of tilt
It is critical that the sander
although 50-grit abrasives are some-
toward the direction of sideways
always be in motion on the metal.
what usable for this purpose. Before
travel. At the end of each lateral
While it is running, it can never stay
metal finishing is complete, the
stroke, as the sander’s direction is
in one spot. If it does, and if you are
metal must be smoothed for paint-
reversed, it is moved the width of its
lucky, you will only overheat the
ing. Although filling follows metal
cut swath, up or down. When the
metal where it dwells, with a very
finishing, it is bad practice to leave
sander’s lateral direction is reversed,
good chance of gouging it. If you are
final smoothing for that stage of this
it should be lifted slightly to avoid
not lucky, you can burn through the
work. It should be the last part of the
dwelling too long on the area where
metal. A telltale dark bluing of the
metal finishing operation. That
the reversal of direction takes place.
metal surface under the disc contact
means that when metal finishing is
You also can accomplish this by
patch will warn you that you are
completed, there should be few, or
untriggering and retriggering the
burning the metal.
no, ridges or sanding marks that
68
AUTOMOTIVE BODY WOR K AN D R UST R E PAI R
M ETAL F I N I S H I NG
need filling. It also means that sur-
should be slightly rounded, to keep
in a fraction of a second. However, a
faces are not so smooth that they
them from tearing apart too easily in
shaped, sided disc presents different
lack the tiny nooks and crannies that
use.
radii of its shape to the metal as it
help paint to mechanically adhere to
In the final stages of metal finish
spins against it, greatly reducing the