Figure 4-24.Using angle iron to cut bevels on steel plate.
Figure 4-23.Typical gouging operation using a low-velocity
cutting jet for better control of depth and width.
more difficult. A preheat temperature of about 500°F is
When cutting cast iron, adjust the preheating flame
of the torch to a carburizing flame. This prevents the
formation of oxides on the surface and provides better
preheat. The cast-iron kerf is always wider than a steel
kerf due to the presence of oxides and the torch move-
ment. The torch movement is similar to scribing semi-
circles along the cutting line (fig. 4-22). As the metal
becomes molten, trigger the cutting oxygen and use its
force to jet the molten metal out of the kerf. Repeat this
action until the cut is complete.
Because of the difficulty in cutting cast iron with
the usual oxygas cutting torch, other methods of cut-
ting were developed. These include the oxygen lance,
carbon-arc powder, inert-gas cutting, and plasma-arc
GOUGING MILD STEEL
Cutting curved grooves on the edge or surface of a
plate and removing faulty welds for rewelding are addi-
tional uses for the cutting torch. The gist of groove
cutting or gouging is based on the use of a large orifice,
low-velocity jet of oxygen instead of a high-velocity jet.
The low-velocity jet oxidizes the surface metal only and
gives better control for more accurate gouging. By
varying the travel speed, oxygen pressure, and the angle
between the tip and plate, you can make a variety of
A gouging tip usually has five or six preheat orifices
that provide a more even preheat distribution. Automatic
machines can cut grooves to exact depths, remove bad
spots, and rapidly prepare metal edges for welding.
Figure 4-23 shows a typical gouging operation.
If the gouging cut is not started properly, it is possi-
ble to cut accidently through the entire thickness of the
plate. If you cut too shallow, you can cause the operation
to stop. The travel speed of the torch along the gouge
line is important. Moving too fast creates a narrow,
shallow gouge and moving too slow creates the oppo-
site; a deep, wide gouge.
BEVELING MILD STEEL
Frequently, you must cut bevels on plate or pipe to
form joints for welding. The flame must actually cut
through 2.8 inches of metal to make a bevel cut of 45
degrees on a 2-inch steel plate. You must take this into
consideration when selecting the tip and adjusting the
pressures. You use more pressure and less speed for a
bevel cut than for a straight cut.
When bevel cutting, you adjust the tip so the pre-
heating orifices straddle the cut. Apiece of l-inch angle
iron, with the angle up, makes an excellent guide for
beveling straight edges. To keep the angle iron in place
while cutting, you should use a heavy piece of scrap, or
tack-weld the angle to the plate being cut. Move the
torch along this guide, as shown in figure 4-24.
ELECTRIC DRIVE CUTTING
An improvement over mechanical guides is an elec-
tric motor-driven cutting torch carriage. The speed of
the motor can be varied allowing the welder to cut to
dimensions and to cut at a specific speed. A typical
motor driven carriage has four wheels: one driven by a
reduction gear, two on swivels (castor style), and one
freewheeling. The torch is mounted on the side of the
carriage and is adjusted up and down by a gear and rack