Tweco PCM-120 Machine Torch - Manual (Page 25)

Manual 0-2698 4-5 OPERATION
A. Piloting
Piloting is harder on parts life than actual cutting be-
cause the pilot arc is directed from the electrode to
the tip rather than to a workpiece. Whenever pos-
sible, avoid excessive pilot arc time to improve parts
life.
B. Torch Standoff
Improper standoff (the distance between the torch
tip and workpiece) can adversely affect tip life as well
as shield cup life. Standoff may also significantly
affect the bevel angle. Reducing standoff will gener-
ally result in a more square cut.
C. Edge Starting
For edge starts, hold the torch perpendicular to the
workpiece with the front of the tip near(not touch-
ing) the edge of the workpiece at the point where the
cut is to start. When starting at the edge of the plate,
do not pause at the edge and force the arc to "reach"
for the edge of the metal. Establish the cutting arc as
quickly as possible.
D. Direction of Cut
In the torch, the plasma gas stream swirls as it leaves
the torch to maintain a smooth column of gas. This
swirl effect results in one side of a cut being more
square than the other. Viewed along the direction of
travel, the right side of the cut is more square than
the left (Refer to Figure 4-6). To make a square-edged
cut along an inside diameter of a circle, the torch
should move counterclockwise around the circle. To
keep the square edge along an outside diameter cut,
the torch should travel in a clockwise direction.
Right Side
Cut Angle
Left Side
Cut Angle
A-00512
Figure 4-6 Side Characteristics of Cut
E. Dross
When dross is present on carbon steel, it is commonly
referred to as either “high speed, slow speed, or top
dross”. Dross present on top of the plate is normally
caused by too great a torch to plate distance. "Top
dross" is normally very easy to remove and can of-
ten be wiped off with a welding glove. "Slow speed
dross" is normally present on the bottom edge of the
plate. It can vary from a light to heavy bead, but
does not adhere tightly to the cut edge, and can be
easily scraped off. "High speed dross" usually forms
a narrow bead along the bottom of the cut edge and
is very difficult to remove. When cutting a trouble-
some steel, it is sometimes useful to reduce the cut-
ting speed to produce "slow speed dross". Any re-
sultant cleanup can be accomplished by scraping, not
grinding.
4.07 Hand Torch Operation
A. Drag or Standoff Cutting With Hand Torch
1. The torch can be comfortably held in one hand or
steadied with two hands. Choose the technique
that feels most comfortable and allows good con-
trol and movement. Position the index finger or
thumb to press the control switch on the torch
handle.
NOTE
The tip should never come in contact with the work-
piece during operation except if drag cutting.
Amperage is limited to 35 Amps when drag cut-
ting.
2. Depending on the type of cutting operation, do
one of the following:
a. For edge starts, hold the torch perpendicular
to the workpiece with the front of the tip on
the edge of the workpiece at the point where
the cut is to start.
b. For drag cuts keep the torch in contact with
the workpiece. Output current is automati-
cally limited to 35 amps.
c. For standoff cutting, hold the torch 1/8 - 3/8
in (3 - 9 mm) from the work .