CFIGURE 2 Note the switch to
change between cutting and gouging,
which also displays the proper air pressure for each. Here, the operator turns
down the amperage to check the proper
air pressure.
CFIGURE 3 Maintaining a 1⁄ 1 16- to ⁄8-
in. standoff increases the longevity of
your consumables, gives you a cleaner
cut, and maximizes your machine’s cutting capacity.
CFIGURE 7 A straight edge helps
guide the torch for more precise cutting.
CFIGURE 4 A drag shield allows you
to rest the torch on the work surface and
maintain the proper standoff distance.
CFIGURE 5 Using your noncutting
hand as a brace gives you freedom of
movement and helps you to maintain a
constant standoff.
CFIGURE 9 A common angle iron can
be used as a guide to make a bevel cut.
CFIGURE 8 A circle-cutting guide helps you make clean, repeatable circular cuts.
First you must make a hole in the center of the workpiece with a center punch to
anchor the cutting guide.
13. Rehearse the cut beforehand
to make sure you have adequate freedom of movement to make one continuous cut. It is difficult to stop and
then continue a long cut cleanly.
A clean cut depends on several factors—travel speed and direction, distance from the work surface, consumables, and technique.
Travel Speed and Direction
Your owner’s manual should contain a
chart that compares material thickness to travel speed in inches per
minute (IPM).
The faster you move (especially on
aluminum), the cleaner your cut will
The FABRICATOR | An FMA Publication
March 2007 | www.thefabricator.com
be. On thick material, set the
machine to full output and vary your
travel speed. On thinner material, you
need to turn down the amperage and
change to a lower-amperage tip to
maintain a narrow kerf.
To determine if you’re going too
fast or too slow, visually follow the arc
that is coming from the bottom of the
cut. The arc should exit the material
at a 15- to 20-degree angle opposite
the direction of travel (see lead
image). If it’s going straight down, that
means you’re going too slowly, and
you’ll have an unnecessary buildup of
dross or slag. If you go too fast, it will
start spraying back. Because the arc
trails at an angle, at the end of a cut,
slow your cutting speed and angle the
torch into the cut through the last bit
of metal.
Human mechanics makes it easier
to pull a torch than to push it. A plasma cut leaves a beveled edge and a
straight edge. Plasma swirls as it exits
the tip, biting one side and finishing
off on the other. An easy way to
remember it is to think of the plasma
torch as a car without reverse. The
torch is always traveling forward, and
the passenger side is always the
straight side. If this is important to
your project, plan accordingly.
Distance From
the Workpiece
When you’re not using a drag shield,
maintain a 1⁄16- to 1⁄8-inch distance
between the tip and the workpiece (see
Figure 3). Although touching the tip
to the work surface adversely affects cut
quality and consumable life, moving
the tip too far away from the workpiece
reduces the cutting capacity of the unit.
Many plasma cutters come with a
drag shield that is placed on the cutting
surface to maintain an optimal 1⁄8-in.
standoff (see Figure 4). This is especially suitable if your hands are
unsteady, or to perform pattern cutting.
This also helps extend tip life.
