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INSTRUMENTOLOGY 45
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(a) Annealing. (i) Place a few smooth broaches on a
plate of iron, heat to **full cherry" redness and allow to cool
slowly. (2) Cover a few more with plaster, pumice or sand,
heat to **full cherry" redness and allow to cool slowly.
Note the difference in result accomplished by the two pro-
cedures. (3) Heat the small end of an excavator blank to
full cherry redness and allow to cool slowly.
(b) Hardening.^—Coat an excavator blank with soap to
prevent overheating and burning out of carbon. Heat to full
cherry redness and plunge in cold, slightly acidulated or
salt water, oil or mercury.
—
(c) Tempering. (i) Heat the shank and blade-end of the
same excavator blank to cherry red and plunge immediately
in any of the above media. Polish on the lathe to remove the
oxides, which have accumulated on the surface. Test with a
file to ascertain if full hardness has been produced. (2) If
so, pass in the flame again and heat the blade-end to a
medium yellow color; plunge immediately (thus tempering
the blade-end), after which again polish to remove the oxides.
(3) Place the small end in contact with a hammer to prevent
drawing the temper at the point, apply the flame back of the
shank and heat to a blue color (spring temper), immediately
plunging in oil, thus tempering the shank.
INSTRUMENTOLOGY
Parts of an Instrument.—Instruments may be divided
—
into those intended to be used by hand ^Hand Instruments
and those for use in the dental engine ^Engine Instruments.
Most instruments consist of three parts, viz.,. (i) Handle or
Shaft, (2) Shank, and (3) Blade or Nib. The Handle or Shaft is
that part which is grasped by the hand in using (Fig. 51). The
Blade is the cutting part of cutting instruments, while the
INSTRUMENTOLOGY 45
—
(a) Annealing. (i) Place a few smooth broaches on a
plate of iron, heat to **full cherry" redness and allow to cool
slowly. (2) Cover a few more with plaster, pumice or sand,
heat to **full cherry" redness and allow to cool slowly.
Note the difference in result accomplished by the two pro-
cedures. (3) Heat the small end of an excavator blank to
full cherry redness and allow to cool slowly.
(b) Hardening.^—Coat an excavator blank with soap to
prevent overheating and burning out of carbon. Heat to full
cherry redness and plunge in cold, slightly acidulated or
salt water, oil or mercury.
—
(c) Tempering. (i) Heat the shank and blade-end of the
same excavator blank to cherry red and plunge immediately
in any of the above media. Polish on the lathe to remove the
oxides, which have accumulated on the surface. Test with a
file to ascertain if full hardness has been produced. (2) If
so, pass in the flame again and heat the blade-end to a
medium yellow color; plunge immediately (thus tempering
the blade-end), after which again polish to remove the oxides.
(3) Place the small end in contact with a hammer to prevent
drawing the temper at the point, apply the flame back of the
shank and heat to a blue color (spring temper), immediately
plunging in oil, thus tempering the shank.
INSTRUMENTOLOGY
Parts of an Instrument.—Instruments may be divided
—
into those intended to be used by hand ^Hand Instruments
and those for use in the dental engine ^Engine Instruments.
Most instruments consist of three parts, viz.,. (i) Handle or
Shaft, (2) Shank, and (3) Blade or Nib. The Handle or Shaft is
that part which is grasped by the hand in using (Fig. 51). The
Blade is the cutting part of cutting instruments, while the
