[Illustration: FIG. 90.--Heat the nose of the tool only up to dotted line, very slowly and thoroughly to an absolutely white welding heat, so that it shows a trifle fused around the edges, and be very sure that this fusing has gone thoroughly through the nose, otherwise the fusing effect will be taken off after the second grinding. Note the difference of the nose between this and Fig. 86.] [Illustration: FIG. 91.--Shows unnecessary roasting and drossing. Such hardening requires a great amount of grinding and is not good. After hardening grind carefully on a wet emery wheel, and be sure that the wheel is sharp with a plentiful supply of water. Do not force the grinding, otherwise the cold water striking the steel heated up by friction, will crack the nose. Be sure that the grinding wheel is sharp.] In grinding all tools should be ground as lightly as possible on a soft wet sandstone or on a wet emery wheel, and care should be taken not to create any surface cracks, which are invariably the result of grinding too forcibly. The foregoing illustrations, Figs. 84 to 91, with their captions, will be found helpful. Special points of caution to be observed when hardening high-speed steel. DON'T use a green coal fire; use coke, or build a hollow fire. DON'T have the bed of the fire free from coal. DON'T hurry the heating for forging. The heating has to be done very slowly and the forging heat has to be kept very high (a full lemon color) heat and the tool has to be continually brought back into the fire to keep the high heat up. When customers complain about seams and cracks, in 9 cases out of 10, this has been caused by too low a forging heat, and when the blacksmith complains about tools cracking, it is necessary to read this paragraph to him. DON'T try to jam the tool into shape under a steam hammer with one or two blows; take easy blows and keep the heat high. DON'T have the tool curved at the bottom; it must lie perfectly flat in the tool post. DON'T harden from your forging heat; let the tool grow cold or fairly cold. After forging you can rough grind the tool dry, but not too forcibly. DON'T, for hardening, get more than the nose white hot. DON'T get the white heat on the surface only. DON'T hurry your heating for hardening; let the heat soak thoroughly through the nose of the tool. DON'T melt the nose of the tool. DON'T, as a rule, dip the nose into water; this should be done only for extremely hard material. It is dangerous to put the nose into water for fear of cracking and when you do put the nose into water put just 1/2 in. only of the extreme white hot part into the water and don't keep it too long in the water; just a few seconds, and then harden in oil. We do not recommend water hardening. DON'T grind too forcibly. DON'T grind dry after hardening. DON'T discolor the steel in grinding. DON'T give too much clearance on tools for cutting cast iron.