Tanks and other sheet metal
can be made from flat pieces of metal welded together but would lack a certain
aesthetic quality. Hammering in some shape makes for an interesting appearance.
Here is a quick overview of simple hammer forming using simple wooden or metal
forms to put shape into sheet metal for tanks, fenders, battery covers or any
other part that can be dreamed up.
Here is an
end cap for a piece of aluminum tube that will eventually become an oil tank. This
cap was hammered over a simple form from .125” aluminum sheet. This is pretty
heavy metal for hammering by hand but when annealed properly, it works rather
easily.
Here are some of the forms used to make this type of
cap. The easier to make forms are just
wood with a radius edged that can be done quickly with a router and radius bit
or carved and sanded to shape by hand. In the far upper right is a wooden
hammer form. Left of the wooden form is a steel hammer form, which will hold up
to many parts. The screws in the form hold a block to the backside so the forms
can be chucked in a lathe for shaping and later clamped in a vise when being
used. The upper left corner of the
picture has a couple of rough shaped caps. Bottom left is a finished cap.
Bottom right is a blank piece of aluminum before shaping.
Here the blank piece of aluminum s clamped between a
hammer form clamped in a vise and a piece of thick aluminum. This top piece
keeps the flat surface from being distorted and can also be a piece of wood but
must leave access for hammering the edges of the blank.
Shaping starts by hitting down the edge in four
places alternating around the perimiter with a flat face mallet. This starts
the forming process and helps keep the blank centered on the form. A plastic
mallet is being used but a wooden or rawhide mallet will work as well. A large
flat face is require as will be discussed later.
Again the edges of the blank are hit down alternating
side to side between the first hits. Note the excess metal sticking out between
this first set of hits. In order to be successful at metal forming a simple
understanding needs to be reached. Basically two actions are required to form
metal, shrinking or stretching. If a hard faced small hammer were used, it
would compress the metal, making it thinner and bigger. In this case, there is
excess metal that needs shrinking. This literally involves forcing the metal
back inside itself to make the metal thicker in the areas that need to shrink.
Continuing to
alternately drive down high spots causes the metal to flow together, thicken
and shrink down to a smaller diameter than the original blank. This whole cap
only takes a few minutes to hammer down.
When the top form is removed, it will be noticed that
some of the excess metal has flowed into the center of the caps causing it to
form a depression. This is fine if it is a desired shape.
Removing the depression is as simple as flipping the
cap over onto a flat hard surface and again using a flat-faced mallet, work
from the outside into the center to force the metal to shrink and flow towards
the center of the cap. A little sanding to remove any scratches and the cap is
ready to weld onto the end of the tank.