torch makes with the direction of the cut, as well as giving a better preheat balance. Manufacturers have developed custom tips for Mapp, propane, and propylene gases to optimize the flames from these alternate fuel gases. The flame is not intended to melt the metal, but to bring it to its ignition temperature. The torch's trigger blows extra oxygen at higher pressures down the torch's third tube out of the central jet into the workpiece, causing the metal to burn and blowing the resulting molten oxide through to the other side. The ideal kerf is a narrow gap with a sharp edge on either side of the workpiece; overheating the workpiece and thus melting through it causes a rounded edge. Cutting is initiated by heating the edge or leading face (as in cutting shapes such as round rod) of the steel to the ignition temperature (approximately bright cherry red heat) using the pre-heat jets only, then using the separate cutting oxygen valve to release the oxygen from the central jet. The oxygen chemically combines with the iron in the ferrous material to oxidize the iron quickly into molten iron oxide, producing the cut. Initiating a cut in the middle of a workpiece is known as piercing. It is worth noting several things at this point: The oxygen flow rate is critical; too little will make a slow ragged cut, while too much will waste oxygen and produce a wide concave cut. Oxygen lances and other custom made torches do not have a separate pressure control for the cutting oxygen, so the cutting oxygen pressure must be controlled using the oxygen regulator. The oxygen cutting pressure should match the cutting tip oxygen orifice. The tip manufacturer's equipment data should be reviewed for the proper cutting oxygen pressures for the specific cutting tip. The oxidation of iron by this method is highly exothermic. Once it has started, steel can be cut at a surprising rate, far faster than if it were merely melted through. At this point, the pre-heat jets are there purely for assistance. The rise in temperature will be obvious by the intense glare from the ejected material, even through proper goggles. A thermic lance is a tool that also uses rapid oxidation of iron to cut through almost any material. Since the melted metal flows out of the workpiece, there must be room on the opposite side of the