Sheet Metal Fabrication Tools
From the Instructors @
The Hot Rod School
Larger Sheet metal fabrication tool are
not a necessity in sheet metal
fabrication, but it sure speeds up the
In this session we will explain briefly
how some of the larger fabrication
Advanced sheet metal shaping:
There are basically only four things that
can be done to metal; cut it, weld it,
stretch it, shrink it. Master these things
and the only limit you have is your
Compound curves are defined as sheet
metal that bends or contours in more
than one direction.
Compound curves make sheet metal
shaping difficult, especially for beginners.
When creating a compound curve, it will
require both shrinking and stretching.
Whenever a sheet metal panel is stretched the
surrounding area will shrink or will need to be shrunk.
When stretching a shape into a flat panel the outer
edges must be shrunk or an effect called the “Bottle
Cap Effect” will occur. The Bottle Cap Effect is when
metal bunches up or puckers around the edge of a
panel being stretched or “worked”, resembling the
wrinkled edges of a bottle cap, these edges must then
be shrunk down to smooth the panel edges and may
help raise the area being stretched.
Sheet Metal Fabrication Tools
Tools used to create compound curves:
Many different tools can be used to create compound curves
whether they are high or low crown, by simply changing dies or
rollers in many of the powered machines you may form many
different high and low crown panels with the same machine.
Below is a list of some of the equipment used to make many
compound curve shapes.
Mallet and tree stump
Mallet and shot bag
Mallet and tree stump procedure:
Make a template or buck to the desired shape, armor makers didn’t have
the luxury of cardboard templates or wooden bucks, instead the suits of
armor were fitted to the man, a “human” buck.
Hollow out the top surface of the tree stump to the general desired shape.
Choose a mallet with the desired finished shape of the panel.
Draw the desired outline of the shape on the panel to be shaped.
Start hammering in the middle of the concave area of the stump working
towards the outer edges. Do not try to get all the shape all at once, work
slowly from the center out.
Notice how the edges of the panel wrinkle (the bottle cap effect) while you
hammer in the center, the edges are trying to shrink themselves. These
wrinkles should be shrunk down during the stretching process, do not wait
until all the stretching has been done. If you wait until finished stretching,
you may fold the wrinkles over and have more difficulty shrinking the outer
The wrinkled edges can be shrunk with a flat, leather or soft wood mallet
or a mechanical shrinker can be used. This is called “cold shrinking”.
Mallet and shot bag procedure:
The shape of the bubble or blister should be
drawn on the panel to be shaped. All hammer
blows should be applied inside this area using
The pneumatic planishing hammer:
Pneumatic planishing hammers became
available in the very early 1930’s and were
very popular in body repair shops through the
late 1950’s. During these years it was more
economical to use labor for body repair
instead of replacement panels.
Shrinkers and stretchers are just that,
machines designed to shrink or stretch metal.
There many different types available, hand
operated, foot operated, and powered (air or
electric). The hand operated is the most
popular because of their low price.
All dies come in sets; shrinking dies have two
upper and two lower dies. These dies are
designed to have sheet metal inserted
between them. When the lever is depressed,
the dies come together, grabbing the metal Kick
and forcing it together, shrinking it. Shrinker
The English Wheel is a very old machine with an uncertain
beginning. One story is that a jewelrysmith in Europe took the
idea from a small rolling mill that manufactured wire stock, and
then made a small frame to hold the two rollers and used it for
smoothing small sheets of gold for jewelry. The idea caught on
and spread through Europe, but seemed to be most popular in
England. This is most likely where the name “English” Wheel
The English Wheel has been used in many countries over the
years, but gained widespread use starting in the very early 1900’s
for shaping automobile and truck bodies and then airplanes.
Mainly used by coachbuilders, some early automobile dealers and
body repair shops purchased miniature hand held versions (called
fender smoothers) of the wheel to run over fenders to smooth the
less than perfect fenders on new cars.
The Wheel is best suited to use after a panel has been shaped in
a shot bag and then the Wheel is used to smooth out the lumps. A
sheet metal panel can be raised completely by using the Wheel
but, for a high crown, the fastest method is to use the shot bag
The Upper Wheel:
Use of the English wheel The large, flat
wheel is free to
spin but is not
The Lower Anvil:
adjustable to set The Lower Anvil:
the amount of Smaller diameter
pressure exerted wheel that is
on the metal. contoured and
controls how much
the panel is stretched,
thus how much crown
is created in the
Use of the English wheel
#1 Anvil #3 Anvil #5 Anvil
Various crowns are available for
creating different amounts of
Use of the English wheel
3/16” Typically Figure 2 Figure 3
Each pass must be straight, consistent and run parallel to the
previous pass. The spacing must be the same across the panel to
ensure a smooth curve without any irregularities or flat spots. This
type of tracking will produce a constant curvature over the entire
The Power Hammer is a very large heavy piece of specialized metal shaping
equipment. While it used to be very popular it is not commonly found in many specialty
car shops today.
The rarity today is primarily because of the size and cost of the machine, plus the low
demand for labor intense coachbuilt cars.
The power hammer is another very old piece of equipment; mechanized hammers
were used at least as far back as the 16th century for hammering metal for plow points,
swords, suits of armor, and horse shoes among other things.
The earliest hammers were of a Helve type; these were nothing more than a hammer
head on the end of a lever. The lever arm was raised and then released by a simple
As time went by, more developing and understanding of mechanical theories evolved.
Better materials and new power sources were invented and more advanced power
hammers were developed.
Because of the noise and the vibrations inventors tried to refine the power hammer,
one type of hammer used an atmospheric cylinder on the machine. The atmospheric
cylinder had a sealed piston and ram, when the ram and piston was raised it created a
vacuum under the piston. When the ram was released the vacuum pulled the piston
down hammering the metal. This still had vibration problems.
Yoder Power Hammer: Fabricated Power hammers are
Yoders are massive cast iron framed metal now available and work very
shaping machines. Note the deep throat depth similar to its big brother.
for large panel shaping capabilities.
The Pulmax is a universal metal forming machine.
Pullmax machines have been used in the sheet metal industry for
many years. The machine's uses are practically limitless.
When using the proper tooling the operator can do -
Hammer forming is basically shaping metal by hitting it with hammers,
mallets, or corking tools over, onto, or into a base form. This base form is
called a hammer form. Some extra tools that will be helpful are a variety
of c-clamps, vise grip style clamps, and a vise. Any one, or all, of these
methods and tools may be used for hammer forming.
Hammer forming is an inexpensive method of sheet metal fabrication,
requiring more skill than money. Even if you are making just one part, the
quality of the part can offset the time spent to make a hammer form, and
on the other hand, a hammer form can save dozens of hours or more if
you are building multiple duplicate parts.
Typically, hammer forms are used on smaller more intricate parts that
must be quite accurate in dimension and contour. The intricate detail
work can be carved or milled into the wood or aluminum hammer form,
then using corking tools the sheet metal can be worked into the designs
or curves and edges.
Uses an upper and lower die through which sheet metal is fed. The dies pinch
the sheet metal and the metal takes on the shape of the die.
Bead rollers are available in both hand crank operated and electric motor
A large variety of dies are available for unlimited shaping possibilities. Custom
dies can be machined when special shapes are required.
bead rolls available for rolling beads in flat panels for additional strength.
step dies available for creating a step or offset in the metal. Ideal for overlaying
panels evenly for a lap style weld. Can also be used to produce many different
Body line roll dies are available for reproducing certain body lines.
radiused roll dies are available for creating a curved edge on sheet metal.
Tank roll radius dies available for creating half radii on sheet metal edges.
When two half radii are welded together a full 90º radius results.
Three stage hem roll dies available for creating a hem on a curved edge.
Big expensive tools are not always needed, but
the do make the job a lot easier and faster.
The number one tool that you really need is to
have your skill level very high. With out high skill
level, the tools will not do much good.
A good Education could help enhance your skill
Try HRI (The Hot Rod School)