ced, but
the diagonals are in the same direction; hence it would be known that D,
F, H, and E were slots or recesses through the piece. The same remarks
apply to piece B, wherein G, J, K are recesses or slots. Piece C is
shown to have in its bore a recess at L. In the case of B, as of A,
there would be no question as to the piece being all one from end to
end, notwithstanding that the two ends are completely severed where the
slots G, I, come, because the spacing and direction of the
cross-hatching are equal on each side of the slots, which they would not
be if they were separate pieces.

[Illustration: Fig. 91.]

[Illustration: Fig. 92.]

Section shading or cross-hatching may sometimes cause the lines of the
drawing to appear crooked to the eye. Thus, in Figure 92, the key edge
on the right appears curved inwards, while on the left the key edge
appears curved outwards, although such is not actually the case. The
same effect is produced in Figure 93 on the right-hand edge of the key,
but not on the left-hand edge.

[Illustration: Fig. 93]

[Illustration: Fig. 94.]

A remarkable instance of this kind is shown in Figure 94, when the
vertical lines appear to the eye to be at a considerable angle one to
the other, although they are parallel.

The lines in sectional shading or cross-hatching may be made to denote
the material of which the piece is to be composed. Thus Professor Unwin
has proposed the system shown in the Figures 95 and 96. This may be of
service in some cases, but it would involve very much more labor than it
is worth in ordinary machine shop drawings, except in the case of cast
iron and wood, these two being shown in the simplest and the usual
manner. It is much better to write the name of the material beneath the
piece in a detail drawing.

[Illustration: Fig. 95.]

[Illustration: Fig. 96.]

LINE SHADING.

Mechanical drawings are made to look better and to show more distinctly
by being line shaded or shaded by lines. The simplest form of line
shading is by the use of the shade or shadow line.

In a mechanical drawing the light is supposed, for the purposes of line
shading or of coloring, to come in from the upper left-hand corner of
the drawing paper; hence it falls directly upon the upper and left-hand
lines of each piece, which are therefore represented by fine lines,
while the right hand and lower edges of the piece being on the shadow
side may therefore, with propriety, be represented