formats,
inexpensive to very expensive. Even if
constructions,
your use for one is only occasional,
and sizes. This is
you still may be able to justify buying
among the best
a less-expensive version of this very
that I have ever
versatile and useful tool. For serious
seen. The main
jobs, the larger and more stable Eng-
issue is stability.
lish wheels work far better than the
A good wheel is
cheap ones.
firm enough to
Planishing hammers are relatively
not get sprung,
inexpensive air-driven power ham-
but resilient
mers that first appeared on the scene
enough to apply
as devices intended for removing dents
great torque
from fenders and from the turret tops
when it is
of some automobiles that arrived in
needed. Note the
the mid 1930s. They are basically C-
foot-tensioning
clamp-shaped frames that hold two
adjustment.
opposing working surfaces: a small
anvil, and a forming hammer. The
hammer is operated as a pneumatic
percussion device, with a rapid cycle
rate. Put simply, metal hammered
between a planishing hammer’s mem-
bers gets pounded, often. The force of
that pounding is adjustable by varying
either the air pressure supplied to the
device, the length of the hammer’s
stroke, or both.
As autobody tools, the original
planishing hammers were pretty poor
because they stretched metal badly.
However, some genius figured out
that if you mount a planishing ham-
mer on a stand, and supply a foot
control for its air supply, you have a
device that is capable of stretching
and forming metal very quickly. Mod-
ern planishing hammers vary from
being very inexpensive tools that use
muffled zip guns to drive their ham-
mers, to being very precise and some-
what expensive tools that are easier to
control, and quite predictable. Again,
This high-end planishing hammer offers considerable precision and
somewhere on that continuum, there
controllability. It is capable of roughing out and moving much metal very
may be a planishing hammer that fits
quickly. Unlike mechanical power hammers and English wheels, planishing
your needs. These tools can do form-
hammers should not be used for finishing operations.
ing very quickly and without rough-
54
AUTOMOTIVE BODY WOR K AN D R UST R E PAI R
C H A P T E R 6
BUMPING TO MOVE THE METAL
THE RIGHT WAY
Bumping is the heavy lifting in
most autobody repair work. Its tools
and techniques also have application
to many fabrication projects. To be
sure, bumping is not always the heavy
lifting in body work. There are repair
jobs that begin on frame machines, or
with body-pulling posts—even heav-
ier lifting than bumping—that are
then followed by bumping opera-
tions. And some body-metal fabrica-
tions never employ bumping. Those
that do may have their heavy lifting
beginnings in sheetmetal brakes, or
on slip rolls, before any bumping
techniques are applied to them.
Bumping means to shape metal to final contours. This rust patch is being
The fact remains, bumping
shaped and bumped into final position so that welding it in can be finished.
describes the group of actions that
Note the use of a square-faced hammer to work up against an edge.
move metal with the likes of ham-
mers and dollies, to push things
These pneumatic tools
pretty much into final shape. This
illustrate the gap between
does not mean that bumping opera-
subtle work and violent
tions, by their nature, require heavy
assault on sheetmetal.
hammering or prying with large
The fender gun (top left)
tools. That may be the case but sub-
is more likely to do harm
tle approaches are also possible.
than good. The
In this regard, let’s consider a
percussion hammer
large area of damage to a low- to
(bottom right) can slowly
medium-crown panel; say, a single
persuade small areas of
impact at one point that deforms 70
metal to move a few
percent of the area of a relatively flat
thousandths of an inch.
AUTOMOTIVE BODY WOR K AN D R UST R E PAI R
55
CHAPTE R 6
door or quarter panel. It may look
think about it, some are much more
terrible because so much metal is dis-
corrective and less destructive than
placed. However, to a seasoned metal
others. It pays to take the time to
worker, it may be possible to return
think about this before you swing
95 percent or more of the damaged
into action.
area to its original contours with a
Backing up metal as you hammer
couple of very undramatic and
and/or pry on it usually saves you
uncomplicated moves. Sometimes,
considerable grief. Hammering off-
most of this kind of damage can be
dolly, or with a dolly, or other back-
pulled out with a suction device, or
ing surface supporting the area
driven out with one, or a few, well-
around where you are hammering, is
aimed blows with a rubber mallet.
At first glance, working with what
usually desirable, unless you intend
Unfortunately, it is just as possi-
almost amounts to a blunt pick
to stretch metal. Using soft backings
ble that attempting to remove this
hammer, over a shot bag, seems to
often works well. These include rub-
kind
of
damage
with
those
be metal finishing. However, the
ber-clad dollies, dollies temporarily
approaches will be unsuccessful. It
hammer is being used to change a
faced with a soft material like corru-
may even inflict further and more
contour in the metal, not just a
gated cardboard, hand-held shot
serious damage to a panel by creating
surface irregularity. That, by definition,
bags, and blocks of soft wood.
ridges, V-channels, and minor upsets.
is bumping.
Using the right impact tools,
The outcome depends on the skill
tools with the right contacting sur-
and judgment of the metal worker.
Another bumping secret is to
faces, is another way to move metal
In this case, the original shape,
work firmly but gently. Usually,
without damaging it. Rubber, plastic,
thickness, and hardness of the panel;
using the least possible force and
and rawhide hammers have a defi-
the depth and configuration of the
impact, and applying it incremen-
nite place in metal bumping opera-
damage to it; any supporting struc-
tally, is the best approach. If you
tions. If a surface will yield to these
ture behind it; and the specific
swing a hammer too hard, or pry
tools, it is often a good idea to use
nature of the tools and maneuvers
metal too far, you will be on the road
them. If not, then harder tools are
employed to remove the damage
to creating problems that are larger
required.
When
hammering
a
determine whether the action fails or
than the ones you started with.
succeeds. In other words, simple
Think before you strike. Always con-
approaches
to
bumping
metal
sider possible alternatives to what
require keen judgments. A rubber
may seem to be the obvious
hammer, used inappropriately, can
approach to removing damage.
cause almost as much damage as a
As you fight the tendency to just
metal hammer.
flail at damaged metal with big,
One scheme for damage removal
nasty tools, it is often important to
that never fails is described and illus-
remember to back up what you are
trated in Chapter 3. It involves ana-
hitting or prying, whether your tool
lyzing how damage occurred, and
is a hammer, dolly, or pry. Whatever
removing it in the reverse order of
you are hammering is attached to
that sequence. What never works is
other metal. As you drive it, you are
simply banging against what seems
driving that other metal. This is how
to be high metal, and hoping that by
bad body workers add unwanted
This combination, a soft rubber mallet
doing so, everything will come out
upsets and stretches to initial dam-
and a corrugated cardboard backing,
alright. That approach will produce
age. It is also critical to hit metal at
is about as mild as it gets. You won’t
additional and severe damage, in the
the right angle. A ridge can be ham-
knock down any ridges this way, but
form of additional deformations
mered or pushed up or down from
you may correct a small defect
with upsets and stretches, galore.
many angles. When you stop to
without creating a bigger one.
56
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
Sometimes, you can make special
tools that greatly speed work and
improve uniformity and quality for
specific bumping jobs. This little die
Even from the back, you can see that this hammer has more crown than the
is used to back up hammering the
reverse crown on the metal that it is hitting. This is necessary, or the hammer
end of a rib into a proper and
face’s outer edges would deform the metal while its center would fail to reach it.
consistent round or spear shape.
crowned surface, a hammer with a
purpose intended. For example, if
equipped with just about every
fairly low crown probably works best
you want to stretch metal, you select
crown and configuration that you
for most purposes because it distrib-
more crown in your backing than if
will ever need. On some occasions,
utes hammering force over a wide
you do not want to stretch metal. In
you may want to create a custom
area, and minimizes denting dam-
the case of dollies, these tools usually
shape to hammer against for a partic-
age. However, dead-flat hammer
offer many different crowns in a sin-
ular purpose or situation. Cutting
faces have limited application to this
gle tool. With about half a dozen dif-
such a shape out of wood, or making
work.
Each
different
situation
ferent
dollies,
you
should
be
it out of metal is often useful.
requires
its
own,
appropriate,
hammer crown. There is no single
hammer that does it all.
When working on reverse-crown
surfaces, a hammer must have more
crown than the surface on which it is
used, or its edges will imprint the
metal, without actually contacting it
at the hammer’s center. Square-faced
hammers are great for working up to
edges, but should not be used in
other situations because their cor-
ners can cause damage to reverse-
crown configurations.
When you hammer against a
reverse-crown area, both on-dolly
and off-dolly, or against any other
unyielding backup surface, the crown
of the support surface should be
Hammering against either of these spoons greatly lessens the chance of a
stray hammer blow damaging the panel. Placing a spoon or pry between your
backing is held against a convex area,
hammer and the metal spreads its force and averages its blow onto a broader
its crown should be chosen for the
surface area.
AUTOMOTIVE BODY WOR K AN D R UST R E PAI R
57
CHAPTE R 6
The other major category of
bumping tools is prying bars and
spoons. These helpful devices come in
an almost limitless variety of sizes and
shapes, and have specific and general
uses. Prying can be difficult to control
and is used primarily where access
problems prevent direct hammering
approaches. For example, when metal
that you need to work on is directly
behind substructure. Some pries are
twisted to move metal, while others
are levered or hammered.
When you hammer on a broad
pry, you are really using it as a body
spoon. Spoons, and pries used as
spoons, are employed to address
areas where access is a problem, or
where it is desirable to spread ham-
mering force over a wide area of
metal. That last case is very impor-
tant. In situations that require the
Dolly-off-dolly is one way to make a swing in very limited space. The dimple
minor movement of a broad area of
removal that is the object of this exercise works, because the hitting dolly�
��s
metal, a spoon will distribute a ham-
face has more crown than the panel’s inside.
mer’s force to accomplish that kind
of
application.
Hammering
on
Let’s take that case a bit further.
dollies, and hammer carefully with
spoons is often overlooked. It is a
If you are working inside a fender to
them on opposite sides of the panel,
very clean and effective approach to
hammer down a ridge, and using a
in opposite directions. Of course,
the problem of moving large
dolly as your impact tool, you run
they must be offset from each other
amounts of surface over small, incre-
the enormous risk of missing the
for this to work.
mental distances.
exact spot that you are trying to
In any specific situation, there
Beyond the rules covering the
hammer out, or of hitting it hard
are almost always numerous ways to
best ways to move metal (without
enough to further damage it. You
approach a bumping task or job. As
unacceptably upsetting or stretching
just don’t have the control over a
you gain experience, you learn
it), and the rules of sequence for
dolly used that way that you would
which ones work best for you, and
attacking complex damage, each
have over a hammer.
you will probably create a few new
metal worker finds his or her own
Here are two solutions to that
ones, as you go along.
comfort level in the choices of proce-
problem: One is to position a spoon
The next step in working metal is
dures and tools to get jobs done. For
on the apex of the ridge, and then
metal finishing, the fine adjustment
example, if a situation requires more
drive the spoon against it with a
of surfaces to near-dimensional per-
hammering pressure than can be
dolly. This would allow more accu-
fection. It is very important that
generated in a small space, it makes
rate positioning of the force than
bumping operations return or bring
perfect sense to use a dolly as your
would be possible with a direct dolly
surfaces very close to correct posi-
hammer. That might be the case
hit. It would also spread the force
tions before metal finishing mea-
when hammering out the side of a
along the ridge, which would
sures are applied. Good metal
fender from behind, when it has
improve the odds on a favorable out-
workers know that a little time spent