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EXCAVATORS. 109 ;
some variations have been made from these forms
embracing, however, the general principles. For in-
stance, the diamond point, as it is familiarly, called, is
a modification of No. 3 in Fig. 18, varying from it in
that it has a sharp point instead of a square edge, and
is three-sided from shaft to point, each angle being a
cutting edge. This instrument is especially valuable
for forming grooves or furrows within cavities, and for
dressing the borders.
Fig. 19.
11
r^ 12
After being much reduced by use, it may still be
kept in form, and sharp, and used as a drill for making
under-cuttings, for which it is very efficient. No. 11
(Fig. 19) represents this instrument.
A modification of No. 9, (Fig. 18), commonly known
as the scoop or spoon-shaped instrument, is exten-
sively used. The sharp corners of No. 9 are removed
in this instrument. It is shown in No. 12, (Fig. 19.)
Of the Manufacture of Excavators.— For making
these instruments, the best cast-steel wire, No. 8.
should be selected. This should be forged down
so as to leave the end large enough to form the
