A number of circular dies of carbon tool steel for use in tool holders of turret lathes were required. No proper tempering oven was available, so the following method was adopted and proved quite successful. After the dies had been hardened dead hard in water, they were cleaned up bright. A pair of ordinary smiths' tongs was made with jaws of heavy material and to fit nicely all around the outside of the die, leaving a 3/32-in. space when the jaws were closed around the die. The dies being all ready, the tongs were heated red hot, and the dies were picked up and held by the tongs. This tempered them from the outside in, left the teeth the temper required and the outside slightly softer. The dies held up the work successfully and were better than when tempered in the same bath. THE EFFECT OF TEMPERING ON WATER-QUENCHED GAGES The following information has been supplied by Automatic and Electric Furnaces, Ltd., 6, Queenstreet, London, S. W.: Two gages of 3/4 in. diameter, 12 threads per inch, were heated in a Wild-Barfield furnace, using the pyroscopic detector, and were quenched in cold water. They were subsequently tempered in a salt bath at various increasing temperatures, the effective diameter of each thread and the scleroscope hardness being measured at each stage. The figures are in 10,000ths of an inch, and indicate the change + or - with reference to the original effective diameter of the gages. The results for the two gages have been averaged. TABLE 24.--CHANGES DUE TO QUENCHING ---------------------------------------------------------------- | After |Tempering temperature, degrees Centigrade Thread |quenching|----------------------------------------- | | 220 | 260 | 300 | 340 | 380 | 420 ------------|---------|------|------|------|------|------|------ 1 | +25 | +19 | +17 | +15 | +13 | +11 | +11 2 | +18 | +12 | +11 | + 9 | + 6 | + 5 | + 5 3 | +12 | + 6 | + 5 | + 3 | 0 | 0 | 0 4 | +10 | + 4 | + 4 | + 2 | ... | 0 | - 1 5 | + 9 | + 4 | + 4 | + 2 | 0 | 0 | 0 6 | + 9 | + 4 | + 3 | + 2 | 0 | 0 | 0 7 | +10 | + 5 | + 5 | + 3 | + 2 | + 1 | + 2 8 | + 8 | + 4 | + 3 | + 2 | 0 | 0 | + 1 9 | + 9 | + 4 | + 3 | + 2 | + 1 | + 1 | + 1 10 | + 9 | + 5 | + 5 | + 3 | + 2 | + 2 | + 2 11 | + 7 | + 4 | + 4 | + 2 | + 1 | + 1 | + 1 12 | + 9 | + 5 | + 5 | + 5 | + 4 | + 4 | + 3 | | | | | | | Scleroscope | 80 | 70 | 70 | 62 | 56 | 53 | 52 ----------------------------------------------------------------