Hardening, tempering, annealing and forging of steel; a treatise on the practical treatment and working of high and low grade steel .. . FIG. 102.—FND MILL. FIG. 103.—FACING MILL. ters for milling tool steel if followed out will be the means of se-curing satisfactory results. HARDENING MILLING CUTTERS. 153 Heat the cutters in a gas furnace, open fire or in a hot leadbath. Not so much depends on the means used for heating asupon how hot and whether uniformly heated;and as to lead stick-ing to the work, if it is used, there should be little trouble if purelead is used with plenty of broken charc
Hardening, tempering, annealing and forging of steel; a treatise on the practical treatment and working of high and low grade steel .. . FIG. 102.—FND MILL. FIG. 103.—FACING MILL. ters for milling tool steel if followed out will be the means of se-curing satisfactory results. HARDENING MILLING CUTTERS. 153 Heat the cutters in a gas furnace, open fire or in a hot leadbath. Not so much depends on the means used for heating asupon how hot and whether uniformly heated;and as to lead stick-ing to the work, if it is used, there should be little trouble if purelead is used with plenty of broken charcoal on top to preventoxidation; but if there is still trouble it can be avoided by coatingthe article with salt before putting into the lead-heating is easily done by warming the work up to a blue and dippingin a strong solution of salt and water. In hardening, the cutters may be cooled in cold water or brine,temperature depending on the character of cutter, whether very. FIG. 104.—HOLLOW MILLS. delicate or not. With some heavy cutters it might be ice cold,while in the case of very thin, delicate cutters it would be betterto have the bath up to blood heat or even higher; it is simply aquestion of preventing cracking. Remove the cutters from the cooling bath as soon as the teethhave cooled sufficiently to harden, and instantly immerse them inoil to remain there, if convenient, until cold. Hozv to Harden HoUozu Mills. When hollow mills are to be hardened, care should be taken when heating not to heat very much above the teeth, as it is not necessary for the back to be hard. When the proper heat has been attained, the mill should be inverted and hardened in the 154 HARDENING, TEMPERING AND ANNEALING, bath with the teeth up, and it should be worked up and downrapidly in the bath in order to force the contents into the results are always attained if this method of dipping isadopted with pieces having holes running part way through them,as then
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