Handbook-Manual Cutting

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MANUAL CUTTING This chapter will cover the mechanics of cutting steel and cast iron with a hand cutting torch or cutting attachment. It will also cover gouging, grooving, and rivet removal. Before making your first cut, be sure to review thoroughly the precautions and safe practices given in Chapter 1. Note especially the precautions which relate to fire prevention. Cutting Steel Plate For your first practice, we suggest that you start with a piece of clean steel plate, about 12 mm (1/2 in.) thick and at least 250 mm (10 in.) wide. Rule a line with chalk or soapstone about 20 mm from one edge of the plate. Place the plate so that this line clears the far edge of your welding table by 25-50 mm. Make sure there is no combustible material nearby which could be ignited by sparks or hot slag. Place a shallow box of dry sand or a piece of sheet steel below the line of cut. If possible, position a piece of sheet metal to deflect sparks that might otherwise reach your pants or your shoes. Be sure to use a cutting nozzle of the size recommended by the manufacturer of your equipment for the thickness of steel to be cut. Adjust oxygen and acetylene pressures to the specific levels recommended in the instructions supplied with your torch or cutting attachment. Then put on goggles, light the torch, and adjust the preheating flames to neutral with the cutting oxygen valve open. Hold the torch in one hand so that you will have easy control of the cutting oxygen valve lever. Use your other hand to steady the torch, usually by resting the torch tubes on top of your closed fist. (If your torch has a 75 deg. head, rather than the right-angle or 90 deg. head, you may find it helpful to place a fire brick under your left fist. Your objective is to position the cutting nozzle so that it is perpendicular to the plate surface.) Before you start cutting, move the flames along the full line of cut, perhaps two or three times, to make sure that you can follow the line without difficulty. To start cutting, hold the torch with the nozzle perpendicular to the surface of the plate and with the flame inner cones not quite touching the plate surface. Center the nozzle over the edge of the plate. As soon as a spot on the edge has been raised to bright red heat, slowly press the cutting oxygen valve lever. There should be a shower of