Page 150 - Robot Builder's Bonanza

THE METALSMITH’S ART 119

BENDING METAL
Most metals can be bent to another shape. Sheet metal is typically transformed into curves
and angles using a tool called a metal brake. Hollow pipe, such as metal conduit for electrical
wiring, is bent using (get this!) a pipe bender.
Not all kinds of metals are as easily bent, at least not without specialty tools. The thickness
of the metal and its overall size, shape, and tempering qualities greatly affect how easy (or hard)
it is to bend. Strips of softer metal like copper and brass bend easily. The thinnest pieces can
be bent by hand; otherwise, you can use a bench vise and rubber mallet to bang it into shape.
Mild steel up to about 1/16″ thick that has not been heat treated (tempered) to make it harder
can be bent using a shop vise and brute force. But you get better results with a metal brake.

Tube bending, especially thin- wall aluminum or brass, requires either skill or a special tool to
G keep the tube from collapsing. The idea is to prevent a sharp kink at the bend. Benders are
available for different sizes of tube. Smaller tubing available at hobby stores can be worked
using a tightly wound spring. With practice, you can also bend lightweight tubing by first filling
it with sand.

Bending causes stress in the metal, which can weaken it. Some aluminum alloys are engi-
neered to be bent, but most of the stuff you find at hardware and home improvement stores
has been hardened. Bending it to more than 20° or 30° can seriously degrade the structure
of the metal. You especially don’t want to bend it in a 90° angle, then back out straight, as the
metal will likely just snap apart.
Metals that have been annealed using a heat treatment are easier to bend. The annealing
makes the metal softer and more ductile. If you need to bend aluminum (up to about 1/8″
thick), find an alloy that has been pretreated using an annealing process. Or you can anneal
the piece yourself if you have a gas welding torch. I’m not going to get into the steps here
(check metalworking books at your local library), but in general you heat up the metal to about
700°F, then allow it to cool slowly back to room temperature. Once cooled, the spot that was
annealed is now softer, and it can be more readily bent to shape.

FINISHING METAL
Cutting and drilling often leave rough edges, called flashing and burrs, in the metal. These
edges should be finished using a metal file or very fine sandpaper. Otherwise, the pieces may
not fit together properly, and the rough edges can scratch skin and snag on carpet. Aluminum
flash comes off quickly and easily; you need to work a little harder when removing the flash
from steel or zinc stock.

If there is a lot of material to remove, use a small grinding wheel attached to a drill motor or
G hobby tool, such as the Dremel. Use the standard Dremel mandrel. It’s composed of two pieces:
a shaft and a screw. Then purchase an aluminum oxide grinding wheel in the shape you need.
Example: Dremel item 541 is a set of two 7/8″-diameter flat wheels made to be mounted with
the mandrel.

Using Metal Files
A metal file is the same as any other file, excepts its teeth— the part that removes the
material— are finer. You should always use a metal file for metal; never use a wood file,

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