Figure 4-21.Progress of a cut in thick steel. A. Preheat flames are 1/16 to 1/8 inch from the metal surface. Hold the torch in this spot
until the metal becomes cherry red. B. Move the torch slowly to maintain the rapid oxidation, even though the cut is only partially
through the metal. C. The cut is made through the entire thickness; the bottom of the kerf lags behind the top edge slightly.
Cutting Thick Steel
Steel, that is greater than 1/8 inch thick, can be cut
by holding the torch so the tip is almost vertical to the
surface of the metal. If you are right-handed, one method
to cut steel is to start at the edge of the plate and move
from right to left. Left-handed people tend to cut left to
right. Either direction is correct and you may cut in the
direction that is most comfortable for you. Figure 4-21
shows the progress of a cut in thick steel.
After heating the edge of the steel to a dull cherry
red, open the oxygen jet all the way by pressing on the
cutting lever. As soon as the cutting action starts, move
the torch tip at a even rate. Avoid unsteady movement
of the torch to prevent irregular cuts and premature
stopping of the cutting action.
To start a cut quicker in thick plate, you should start
at the edge of the metal with the torch angled in the
opposite direction of travel. When the edge starts to cut,
bring the torch to a vertical position to complete the cut
through the total thickness of the metal. As soon as the
cut is through the metal, start moving the torch in the
direction of travel.
Two other methods for starting cuts are used. In the
first method, you nick the edge of the metal with a cold
chisel at the point where the cut is to start. The sharp
edges of the metal upset by the chisel will preheat and
oxidize rapidly under the cutting torch, allowing you to
start the cut without preheating the entire edge of the
plate. In the second method, you place an iron filler rod
at the edge of a thick plate. As you apply the preheat
flames to the edge of the plate, the filler rod rapidly
reaches the cherry red temperature. At this point, turn
the cutting oxygen on and the rod will oxidize and cause
the thicker plate to start oxidizing.
CUTTING CAST IRON
It is more difficult to cut cast iron than steel because
the iron oxides in cast iron melt at a higher temperature
than the cast iron itself. Before you cut cast iron, it is
best to preheat the whole casting to prevent stress frac-
tures. Do not heat the casting to a temperature that is too
high, as this will oxidize the surface and make cutting
Figure 4-22.Torch movements for cutting cast iron.