to change the numbers to conform to the pyrometer
readings. Readings of the temperatures of the carburizing furnaces
are taken and tabulated every ten minutes. These, numbered 1 to
10, are shown on the board to the right in Fig. 59. The card shown
in Fig. 61 gives such a record. These records are filed away for
possible future reference.

[Illustration: FIG. 58.--Gas heated drawing plate for tooth ends.]

The temperatures of the reheating furnaces, numbered from 1 to
26 and shown on the board to the left in Fig. 59, are taken every
5 min.

Each furnace has a large metal sign on which is marked the temperature
at which the furnace regulator is required to keep his heat. As
soon as any variation from this is posted on the board outside
the pyrometer room, the attendant sees it and adjusts the burners
to compensate.

[Illustration: FIG. 59.--Pyrometer recording room.]

[Illustration: FIG. 60.--Inside of Pyrometer switch room.]

DIES FOR GLEASON TEMPERING MACHINES.--In Fig. 62 is shown a set
of dies for the Gleason tempering machine. These accurately made
dies fit and hold the gear true during quenching, thus preventing
distortion.

[Illustration: FIG. 61.--Carburizing furnace record.]

Referring to Fig. 62, the die _A_ has a surface _B_ which fits the
face of the teeth of the gear _C_. This surface is perforated by
a large number of holes which permit the quenching oil to circulate
freely. The die _A_ is set in the upper end of the plunger _A_
of the tempering machine, shown in Fig. 63, a few inches above
the surface of the quenching oil in the tank _N_. Inside the die
_A_ are the centering jaws _D_, Fig. 62, which are an easy fit
for the bore of the gear _C_. The inner surface of the centering
jaws is in the shape of a female cone. The upper die is shown at
_E_. In the center (separate from it, but a snug sliding fit in
it) is the expander _G_, which, during quenching, enters the taper
in the centering jaws _D_, expanding them against the bore of the
gear _C_. The faces _F_ of the upper die _E_ fit two angles at the
back of the gear and are grooved for the passage of the quenching
oil. The upper die _E_ is secured to the die carrier _B_, shown in
Fig. 9, and inside the die is the expander _G_, which is backed
up by compression springs.

[Illustration: FIG. 62.--Dies for Gleason gear-hardening machine.]

HARDENING OPERATION.--Hardening a gear is accomplished as follows:
The gear is taken from the furnace by