Illustrated Theatre Production Guide, 2nd Edition

342 Illustrated Theatre Production Guide 2 ed

has approximately the same strength and rigidity as a

2×4. Some small units are better constructed from 1″

or even

3

4

″

stock when that rigidity is not required.

Structural Design for the Stage, by Holden and Sammler

(Focal, 1999), is an excellent resource for anyone inter-

ested in studying the structural properties of specific

materials.

Structural steel tubing of the sort used to construct

scenery is composed of mild steel, a name given to steel

with a low carbon content that has excellent malleability

and a Rockwell C scale hardness number in the 20s. It

is easily drilled with ordinary tools.

WELDING EqUIPMENT

Two very common types of welders are used to join

steel. One is the generic arc welder and the other is

the metal inert gas type, which is abbreviated as MIG. A

MIG welder is by far the easiest kind of welder

to use for welding mild steel and is far and away the

most popular choice. A MIG welder is somewhat

more expensive to purchase than a standard arc welder,

because its mechanism is much more complicated.

An arc welder is essentially a very large rectifier unit

that changes AC power into DC power. Electronically,

some machines are constant current while others are

constant voltage. Two long cables are attached to the

output of the machine. The ground has a clamp on the

end that gets connected to the steel you are welding.

The other cable has a smaller clamp to hold an electrode,

which is a consumable wire stick coated with flux. The

flux is a catalyst that aids in the welding process by

producing CO

2

gas when heated by the welding process.

The CO

2

gas prevents the steel from oxidizing at high

temperatures. When the electrode is brought into close

contact with the steel, a circuit is completed between

the (usually) positive output of the welder, the elec-

trode, the steel being welded, the ground clamp, and

the negative terminal of the welder.

Because the electrode is only tangentially in contact

with the steel, the electricity must jump across that small

gap in order to complete the circuit. When that happens,

a small spark or arc is created. The arc is very hot and

melts the steel. The electrode gets hot also, and the tip

of it melts as well. Protected by the flux, molten steel

from the electrode mixes with the molten steel on the

edges of the joint being welded. Three pieces of steel are

being melted and joined: the two pieces being con-

nected and the electrode from the welder itself. When

the molten steel cools and hardens, all three should be

joined at the molecular level, so that theoretically they

are all one homogeneous crystalline structure. (In reality,

the heating and cooling make a slight difference in the

composition of the welded area.)

There are several fairly problematic consequences

of arc welding. Of course the light produced is extremely

bright and will cause serious injury to your eyes if you

look at it from a close distance. (The distance from the

arc while you are welding is very, very close.) Special