Handbook-Manual Cutting

When you have completed your first cut, you may find that the scrap section does not fall freely. What has

happened is that the dross produced by the cutting reaction has bridged the gap created by the oxygen stream. This dross is quite brittle, and the scrap section, once the metal has cooled a bit, can be easily detached with a quick rap from a hammer. If you value your equipment, don’t use your torch head instead of a hammer. One blow may do the torch no harm, but if you let yourself get into the habit of knocking off the scrap with the torch, you will probably wind up paying a substantial repair bill before many months have passed. After you have made the first cut, we suggest that you compare the surface of the cut edge with the photographs given in Fig. 21-2. They should provide you with some clues as to what you did wrong (we are assuming that no one can make a perfect cut on the first try). Then make a second cut, a third, and a fourth, stopping after each to examine the cut surface closely and decide what to do differently on the next cut. You will probably be surprised and pleased to see how clean your fourth cut looks. Bevel Cutting Cutting right straight through plate is relatively easy. Making a good bevel cut in plate of the same thickness is considerably more difficult. Since one of the major uses of the cutting torch is to bevel plate edges in preparation for welding, you must master the art of bevel cutting before you can feel ready to use your equipment to best advantage. Assuming that you started to practice on plate about 12 mm (1/2 in.) thick, and that you are going to try making a 45-deg. bevel cut in the same material, the first thing you should do (assuming that you had the correct size nozzle in the first place) is to change the nozzle in your torch. In a 45- deg. bevel cut, the actual depth of cut will be 1.4 times the thickness of the plate itself. So move up to a nozzle one size larger; if it is a four-flame nozzle, position the nozzle in the torch head rather carefully. In making square cuts with a four-flame nozzle, it helps a bit to have one flame directly leading the cut. In bevel-cutting, the four-flames should straddle the cut line evenly – two on each side. Continued on next page...