r, 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
----------------------------------------------------------------

Had these gages been formed with a plain cylindrical end projecting
in front of the screw, the first two threads would have been prevented
from increasing more than the rest. The gages would then have been
fairly easily corrected by lapping after tempering at 220 deg.C. Practically
no lapping would be required if they were tempered at 340 deg.C. There
seems to be no advantage in going to a higher temperature than
this. The same degree of hardness could have been obtained with
considerably less distortion by quenching directly in fused salt. It
is interesting to note that when the swelling after water quenching
does not exceed 0.0012 in., pra