Figure 5-40.-A non-isometric line (AB) in an isometric
projection.
a NON-ISOMETRIC LINE is a line that is not
parallel to any one of the three legs of the
isometric axis. It is not a normal line in a normal
multi-view projection of the object.
The upperpart of figure 5-40 shows a two-
view normal multi-view projection of a block.
Though the line AB is parallel to the horizontal
plane of projection, it is oblique to both the
vertical and the profile planes. It is therefore
not a normal, but an oblique, line in the multi-
view projection, and it will be a non-isometric
line in an isometric projection or drawing of the
same object.
The line AB appears in its true length
in the top multi-view view because it is parallel
to the plane of the view (the horizontal plane);
but it will appear as a non-isometric line,
and therefore not in its true length, in an
isometric drawing, as shown in the bottom
part of figure 5-40. It follows that you cannot
transfer AB directly from the multi-view
projection to the isometric drawing. You can,
however, transfer directly all the normal lines in
the multi-view projection, which will be isometric
lines appearing in their true lengths in the
isometric drawing. When you have done this, you
will have constructed the entire isometric draw-
ing, exclusive of line AB and of its counterpart
on the bottom face of the block. The end points
of AB and of its counterpart will be located,
however, and it will only be necessary to connect
them by straight lines.
Angles in Isometric.—In a normal multi-view
view of an object, an angle will appear in its true
size. In an isometric projection or drawing, an
angle never appears in its true size, Even an angle
formed by normal lines, such as each of the
90-degree corner angles of the block shown in the
bottom part of figure 5-41, appears distorted in
isometric.
The same principle used in transferring
a non-isometric line is used to transfer an
angle in isometric. The upperpart of figure 5-41
shows a two-view multi-view projection of a
block. On the top face of the block, the line
AB makes a 40-degree angle with the front
edge. The line AB is an oblique (that is, not
normal) line, which will appear as a non-isometric
line in the isometric drawing. You locate the end
points of AB on the isometric drawing by
Figure 5-41.-Drawing an angle in isometric.
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