```Engineering 28
University of California
• Lecture # 9
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Orthogonal projection
Multi-view presentation
Third-angle projection
First-angle projection
Presentation for Fabrication
• Features
hidden
• Lengths
distorted
• Angles
distorted
• Hard to draw
• Hard to scale
Problems with Pictorials
• Circles distorted
• Curves distorted
• Hard to visualize
curvature in a
plane, e.g. for
tool paths
• Hard to draw
curves
Orthographic Projection
• Projection of a 3-D object on a plane by
rays perpendicular to that plane
Fault (Benefit) of
Orthogonal Projection
Part Placement
View Interpretation
Multi-view Presentation
• Presents more than one view of an object on
the same viewing plane
• Can see features from different directions
• With enough views, can see and
characterize all features
• “Glass Box” approach
Glass Box
interpretation
Third-Angle
Projection
Note alignment and
orientation of views
ANSI Standards (Y14.5)
• Adapted by drafters and engineers to
expedite the transfer of information.
• Maximum information with the minimum
drawing.
• Too many, and to boring, to go though all in
class, check reference if necessary.
• Some highlights...
ANSI Standards (Y14.5)
• Orthographic views used
– As many lines in true length and as many
planes in true shape as possible
– Multiple views from the glass box
• Don't show the intersection lines of the
orthographic planes.
• Section views used for clarification of
internal geometries
ANSI Standards (Y14.5)
• Shapes are simple
– Extended from basic machine tools
– Planes and holes (shafts) easy to make
• Lines assumed to be intersections of planes
• Circles assumed to be intersections of
cylinders and orthogonal planes
Preferred Presentation
ANSI Standards (Y14.5)
• Add more views as required so the
dimensions of the object can be defined
entirely in true length measurements
• Add more views as necessary for
presentation clarity
• Tangent edges are usually not shown
ANSI Standards (Y14.5)
• Use hidden lines to add information, clarity.
• Do not use overuse hidden lines (not wrong,
just poor practice)
• Use centerlines to mark the centers of holes,
or cylindrical surfaces 180º
How Many Views?
Unnecessary
How Many Views?
Two views fine
How Many Views?
How Many Views?
How Many Views?
How About Hidden Lines?
Optional
Preferred Presentation
Guidelines for Presentation
• Start with showing the object in the
preferred configuration, i.e. the top, front
and right side views. Orient the object such
that as many edges as possible are shown in
their true length in these views.
• Add more of the standard orthogonal views,
e.g. left side, bottom, and/or back view, as
necessary such that dimensioning can be
applied to visible edges or features only.
Guidelines for Presentation
• Add all the hidden lines from the exterior
edges and interior detail that are not visible.
• If there are too many hidden lines, and the
views are confusing, remove the hidden
lines that are not necessary for fully
defining the geometry or features of the
object.
Guidelines for Presentation
• If there are still too many hidden lines, and
the views are still confusing, add more of
the standard orthogonal views as necessary
to reduce the number of hidden lines and
maintain full definition of the object’s
geometry.
First-Angle Projection
• Used in parts of Europe and Asia
First-Angle Projection
Note alignment and
orientation of views
1st vs. 3rd Angle Projection
Correct, even though it’s wrong…
ANSI Standards (Y14.5)
• Small radii, intersections of blended planar
surfaces shown as a line
ANSI Standards (Y14.5)
• Schematics used, i.e. for screws
ANSI Standards (Y14.5)
ANSI Standards (Y14.5)
• Small cuts on curved surfaces
ANSI Standards (Y14.5)
• Small protrusions from curved surfaces
Parts with Odd Rotational
Symmetry
End
• Questions?
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