been pushed in, and where there is
come. The second solution, which
getting bumping right can save sig-
insufficient room to swing a hammer.
takes skill and practice, is to use two
nificant time in metal finishing.
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AUTOMOTIVE BODY WOR K AN D R UST R E PAI R
B U M P I NG TO MOVE TH E M ETAL TH E R IG HT WAY
The Case of Bumping the
Run Down Spare Tire Cover
The panel in front was
clamp a couple of times, and he hit the
dragged and flattened. The
wooden ram board with a rubber hammer
one in the rear is in near
a few times, for added persuasion. As he
perfect shape, and can be
tightened and hammered, he levered up
used as a model for
one edge of the panel with a soft pry. In
reshaping the damaged
just a few minutes he had the panel
panel. The Door County
bumped into pretty good shape.
Civil Defense Auxiliary
Next, he checked the profile shape of
Police sticker on the good
the tire cover against a template that he
panel is probably unique.
had made out of cardboard from a good
spare tire cover, and found it bent and
We wil never know who ran down this rubber, plastic, or rawhide malets, I warped in a couple of places. Since the Triumph TR-3 spare tire cover. But
reached for one of our large dol ies, to
original accident and our lever press
my friend, Herb Statz, who worked with me
begin bashing out the worst of it.
bumping ministrations had not caused any
to fix it, had a first-class idea for bumping
Herb stopped me before I struck with
upsets or stretches in the panel, a little
out most of the damage to it in a few easy
the dolly, saying, “Hey, let me try some-
careful bumping with a dead-blow plastic
moves.
thing.” Then, using some scrap wood and
mallet returned it to its original format, with
The cover had been dragged and flat-
some large C-clamps, he rigged a small
no further actions needed.
tened by the time that we received it, and
metal table as a lever press. In a couple of
I suspect that if Herb had not inter-
the license plate part of the panel was
moves, he had the panel pushed back to
vened, convincing me to use his lever press
severely pushed in and leveled. Since the
its original depth, and pretty well straight-
method instead of my big-hammer approach,
damage was too locked-in to remove with
ened out. He had to tighten the levering
we would have spent a much longer time try-
Using some old wood scraps and a
couple of large C-clamps, it took
Herb Statz just a few minutes to
Some of the straightening work
devise and implement this
With the basic damage repaired,
was done with a dead-blow
makeshift lever press. With a little
Herb made a cardboard model of
hammer on the panel’s back, and
help from a rubber hammer and a
both sides of the good panel, to
more was done to reshape its
plastic pry, he quickly restored the
compare shapes. He then corrected
edges. Herb’s technique for
panel’s basic shape, with no
the areas of the damaged panel
removing the worst damage
collateral damage.
that were warping it.
minimized the panel’s warping.
AUTOMOTIVE BODY WOR K AN D R UST R E PAI R
59
C H A P T E R 7
METAL FINISHING
In the metal
and shaving metal off them, to
finishing stage of
make small dimensional and curva-
body work, final
ture changes.
panel contour
For those reasons, I think that
adjustments are
metal finishing is the most critical
made and most
stage of this work. It may lack the
surface defects
visually dramatic outcomes of bump-
are removed.
ing, but when it is done well, it is the
Making a final
part of metal work that produces
correction to the
much of the wow factor in great
contour of a
autobody repairs and fabrications.
sectioned door is
One copasetic aspect of metal
shown here. Note
finishing is that the tools used to
that Blaine is
accomplish it are refreshingly few,
working with his
simple, and relatively inexpensive.
sightline aligned
Of course, there is an offsetting
with the panel’s
downside to that proposition: You
surface.
have to use those tools correctly to
get good results, and that is not
always easy. This chapter focuses
on the correct use of metal finish-
ing tools—body files, pick ham-
mers, and disc sanders—to achieve
great results.
Metal finishing is the critical
faces are filled, just before panels are
step in preparing metal for painting.
painted. By its nature, metal finish-
Indicating, Feeling and Other
It occurs between the bumping
ing is finer work than bumping, yet
Human Tools to Determine
stage, where metal is hammered,
offers more latitude for correction
Panel Surfaces
pried, pushed, or pulled into shape,
than the filling stage that follows it.
and the filling stage, where very
In metal finishing, you can still
If you need to change the contour
small defects in metal-finished sur-
modify surfaces by moving them
of a panel, it should be done before
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AUTOMOTIVE BODY WOR K AN D R UST R E PAI R
M ETAL F I N I S H I NG
case with character lines of various
configurations (for example, 1960s
phony louvers in some Chrysler
products’ rear fender flanks).
It is this feature, the smoothness
of crowns and combination crowns,
that metal finishing must preserve. It
also must level minor surface devia-
tions, in the form of small bumps
and depressions. Metal finishing is
the last appeal in the matter of panel
crown continuity. It is also very close
to the last appeal in the matter of
panel smoothness.
Unlike bumping, where you can
sense surfaces visually, and by feeling
them, metal finishing works at a
finer level. It works at the edge of the
ability of the human sense of touch
These two tools illustrate the difference between bumping and metal finishing.
to sense deviations, and beyond the
The pneumatic body hammer (top left) has a 1-inch stroke, for movin
g metal
capabilities of unaided visual inspec-
and removing ridges. The pneumatic percussion hammer (bottom right) can
tion of unpainted metal surfaces to
pick light metal a few thousandths of an inch in metal finishing work.
define consistency. The solution to
metal finishing operations begin. But if
you need to make sure that a contour
is perfectly consistent in very small
dimensions, and that it is contained in
a nearly perfect surface, metal finish-
ing is where you get these results.
Any crown or combination of
crowns in a panel must flow
smoothly—by itself, or as one crown
into another. If the requirements of
practical matters, like covering up
vehicle mechanisms, or opening
doors, requires a panel surface to be
discontinuous in crown, well, that is
why stylists employ creases, charac-
ter lines, and the other discontinu-
ous or angular ploys and styling
times, I suppose, they do these
things just for fun. What autobody
panels do not have is irregular and
Body files come in many sizes, shapes, tooth counts, and configurations.
illogical interruptions to the flow of
These are unusual, special-purposes files. None of them are currently
crowns, unless such features are con-
available, but they do show up at swap meets and auctions. There are
sistent and repeated, as can be the
situations where they work much better than flat files.
AUTOMOTIVE BODY WOR K AN D R UST R E PAI R
61
CHAPTE R 7
exceeding those human limits is to
find deviations with files and disc
sanders. Once these are located,
metal finishing procedures work to
correct them. In the case of low
spots, the deviations are raised with
hammers, usually pick hammers,
and leveled with more filing or disc
sanding. If the deviations are bumps
(projections), they are filed or
sanded to level.
These are very fine adjustments,
involving as little as 1 or 2 thou-
sandths of an inch. In a 20-, 21-, or
22-gauge panel, there is not much
thickness to file or sand off, without
rendering that area of the panel dan-
gerously thin. The point is: You must
have a panel correct and level before
The coarse file (top) has a 6-per-inch tooth count, while the fine file (bottom)
metal finishing is a reasonable
sports an amazing 16 teeth per inch. Most body files are in the 8-tooth-per-
approach to achieving final contours
inch range, ideal for most jobs. Finer files than that are for very fine finishing
and smoothness.
jobs and for working on aluminum panels.
The first metal finishing tool that
you should learn to use is the 14-inch
body file. It is a masterpiece of func-
tional tool design, evolved to perfec-
tion over many years of development.
Used correctly and in moderation, it
can do wonderful things for you.
Foremost among these things is filing
off high spots and revealing low spots
in panels. It does this by slightly cut-
ting away surface metal above low
spots, and leaving them visually obvi-
ous as slight voids in an otherwise
continuous, filed, shiny surface.
Once low spots are located, they
can be raised with hammers and/or
pick hammers, and re-filed. This
process is repeated until no low spots
are revealed, at which point the panel
surface is level. However, it cannot be
repeated ad infinitum, because each
filing cycle removes metal and makes
a panel thinner. You need to accom-
These are the basic file holders that I use. They offer comfortable gripping
plish leveling in three or fewer filing
surfaces and can be rocked, toe to heal, naturally. The flexible holder (bottom)
applications, and that third one
offers adjustable contour, from mild concave to mild convex, and is the most
should be very light.
usable holder for general work.
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AUTOMOTIVE BODY WOR K AN D R UST R E PAI R
M ETAL F I N I S H I NG
Pick hammering takes skill and
practice. Some inventions purport to
make it easier. These pneumatic
picks are placed against low spots
and triggered with foot valves. True,
you don’t have to hit an invisible spot
from afar with them, but they are
difficult to locate and hard to control.
Always keep in mind that the
object of metal finishing is to achieve
correct contours and smooth metal
with a minimum of material removal.
The proper motion with a body file is forward, away from you, and slightly side-
Beyond that, try to leave as little need
ways. As the file is moved, your down force on it should be shifted from its front
for body filler—plastic or metal—as is
to its back. You should always file toward areas of lower crown.
possible. After metal finishing, it is
best to use little or no filler.
Filing Done Right
All 14-inch, flat, body files come
in a variety of tooth counts—
between 6 and 16 teeth per inch. The
finer files tend to cut more smoothly,
but to remove less metal in a stroke
somewhat easier to use. They are
intended for finishing work. A body
file with 8 teeth per inch is good for
general metal finishing work.
Although it is possible to sharpen
dull files several times, it is difficult to
find file sharpening services these
days, so it is best to try to keep your
files sharp for as long as possible. One
trick to accomplish this is to brush
From the gallery of great ideas that just don’t work, I offer spring-loaded, auto-
their teeth lightly with turpentine,
matic Bulls-eye picks. Supposedly, you locate the target anvil over a low spot, and
from time to time. This retards rust
squeeze the handle. Bingo, raised metal. But most situations lack room to fit
and lubricates the cutting action. It
these clunky devices, and they never strike accurately enough to work.
AUTOMOTIVE BODY WOR K AN D R UST R E PAI R
63
CHAPTE R 7
The Sanding-Picking-Filing-Sanding
Metal Finishing Routine
The repair of two small dents in a up with a small, highly crowned body ham-
At this point, the panel was filed with
1948 Chrysler decklid illustrates
mer, which reduced its size by more than
a flat 8-tooth-per-inch body file, held in a
the basic sanding-picking-filing-sanding
half of its diameter. Then, we used a blunt
slight curvature in a flexible file holder. The
sequence that is used
in metal finishing.
pick hammer to finish lifting its center.
first hammering and picking operation
This process indicates low spots, grinds
off high spots, and ensures crown
continuity in panels. It is also used to
raise and repair small dents.
The first step was to disc sand the
paint off the panel, in the area of the two
small dents that are the subjects of this
repair. Since the rest of the panel was
undamaged, and because our plan called
for chemically stripping the panel after the
dents were repaired, we disc sanded it
only in an area that included the two
spots. This would allow us to check crown
continuity in that area, after we made nec-
Sanding the paint off this
1
essary repairs.
decklid revealed the extent
The smaller dent was driven
2
The sanded area revealed the extent
of the two medium-sized dents that
up with a blunt pick to raise
of each dent. It was about what we
were the reason for the repair. Both
its deepest area and, at the same
expected, and well within the range of
were perfect candidates for
time, to slightly raise the entire
what it is possible to repair by lifting up
hammering up from the other side,
area around it. Picking has to be
and filing metal. Our first step was to pick
and metal finishing, because both
done with the intent to completely
up the smaller spot with a fairly blunt pick
offered good access for that
level entire damage spots.
hammer. The larger spot was first driven
procedure.
We used a dolly that wrapped
4
around two sides of the dent
to back up our hammering. This
controlled the movement of the
panel area just adjacent to the
The areas around and between the dents were sanded to bare
dent. Hammering was done off-
3
metal, so that the repair could account for the crown in the entire
dolly, and the dolly was shifted from
repair area. The dent on the left is more complex than the one on the right.
time to time around the dent.
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AUTOMOTIVE BODY WOR K AN D R UST R E PAI R
M ETAL F I N I S H I NG
tends to double the life of a new or
sharpened file, and helps you achieve
the proper smooth-gliding motion.
Body files are held in file holders
made of wood or metal. I tend to use