Figure 4-19.The effect of moving a cutting torch too rapidly
across the work.
Figure 4-18.Position of torch tip for starting a cut.
Hold the torch perpendicular to the work, with the inner
cones of the preheating flames about 1/16 inch above
the end of the line to be cut (fig. 4-18). Hold the torch
in this position until the spot you are heating is a bright
red. Open the cutting oxygen valve slowly but steadily
by pressing down on the cutting valve lever.
When the cut is started correctly, a shower of sparks
will fall from the opposite side of the work, indicating
that the flame has pierced the metal. Move the cutting
torch forward along the line just fast enough for the
flame to continue to penetrate the work completely. If
you have made the cut properly, you will get a clean,
narrow cut that looks almost like it was made by a saw.
When cutting round bars or heavy sections, you can save
preheating time by raising a small burr with a chisel
where the cut is to begin. This small raised portion will
heat quickly, allowing you to start cutting immediately.
Once you start the cut, you should move the torch
Slowly along the cutting mark or guide. As you move
the torch along, watch the cut so you can tell how it is
progressing. Adjust the torch as necessary. You must
move the torch at the correct speed, not too fast and not
too slow. If you go too slowly, the preheating flame
melts the top edges along the cut and could weld them
back together again. If you go too rapidly, the flame will
not penetrate completely, as shown in figure 4-19. When
this happens, sparks and slag will blow back towards
you. If you have to restart the cut, make sure there is no
slag on the opposite side.
Figure 4-20.Recommended procedure for cutting thin steel.
Notice that the two preheat flames are in line with the cut
Cutting Thin Steel
When cutting steel 1/8 inch or less in thickness, use
the smallest cutting tip available. In addition, point the
tip in the direction the torch is traveling. By tilting the
tip, you give the preheating flames a chance to heat the
metal ahead of the oxygen jet, as shown in figure 4-20.
If you hold the tip perpendicular to the surface, you
decrease the amount of preheated metal and the adjacent
metal could cool the cut enough to prevent smooth
cutting action. Many Steelworkers actually rest the edge
of the tip on the metal during this process. If you use this
method, be careful to keep the end of the preheating
flame inner cone just above the metal.