Microsoft Word - lecnote_fm_engineering drawing

Figure 5.11 First angle projections

5.2.2 Classification of surfaces and Lines in

Orthographic Projections

Any object, depending upon its shape and space position may
or may not have some surfaces parallel or perpendicular to
the planes of projection.

Surfaces are classified according to their space relation ship
with the planes of projection i.e. horizontal, frontal and profile
surfaces. When a surface is inclined to two of the planes of
projection (but perpendicular to the third, the surface is said to
be auxiliary or inclined .It the surface is at angle to all three
planes, the term oblique or skew is used

Although uniform in appearance, the lines on a drawing may
indicate three different types of directional change on the
object. An edge view is a line showing the edge of a
projection. An intersection is a line formed by the meeting of
two surfaces where either one surface is parallel and one at
an angle or both are at an angle to the plane of projection. A