The heating for forging should be done preferably in a pipe or muffle furnace but if this is not convenient use a good clean fire with plenty of fuel between the blast pipe and the tool. Never allow the tool to soak after the desired forging heat has been reached. Do not heat the tool further back than is necessary to shape the tool, but give the tool sufficient heat. See that the back of the tool is flatly dressed to provide proper support under the nose of the tool. HARDENING HIGH-SPEED STEEL.--Slowly reheat the cutting edge of the tool to a cherry red, 1,400 deg.F., then force the blast so as to raise the temperature quickly to a full white heat, 2,200 to 2,250 deg.F., that is, until the tool starts to sweat at the cutting face. Cool the point of the tool in a dry air blast or preferably in oil, further cool in oil keeping the tool moving until the tool has become black hot. To remove hardening strains reheat the tool to from 500 to 1,100 deg.F. Cool in oil or atmosphere. This second heat treatment adds to the toughness of the tool and therefore to its life. GRINDING TOOLS.--Grind tools to remove all scale. Use a quick-cutting, dry, abrasive wheel. If using a wet wheel, be sure to use plenty of water. Do not under any circumstances force the tool against the wheel so as to draw the color, as this is likely to set up checks on the surface of the tool to its detriment. FOR MILLING CUTTERS AND FORMED TOOLS FORGING.--Forge as before.--ANNEALING.--Place the steel in a pipe, box or muffle. Arrange the steel so as to allow at least 1 in. of packing, consisting of dry powder ashes, powdered charcoal, mica, etc., between the pieces and the walls of the box or pipe. If using a pipe close the ends. Heat slowly and uniformly to a cherry red, 1,375 to 1,450 deg.F. according to size. Hold the steel at this temperature until the heat has thoroughly saturated through the metal, then allow the muffle box and tools to cool very slowly in a dying furnace or remove the muffle with its charge and bury in hot ashes or lime. The slower the cooling the softer the steel. The heating requires from 2 to 10 hr. depending upon the size of the piece.