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THEORY OF SHAPE
DESCRIPTION
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Orthographic Representations
The normal technical drawing is often anorthogonal projection
2-D representation requires an understanding ofboth the projection methods and their
interpretation
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To show the object completely, the six views inthe directions A, B, C, D, E, and F may be
necessary
The most information view of
the object is normally chosen
as the principal view
Generally shows the object
in the functioning,
manufacturing, or
mounting position
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Method of Representation
Third-Angle Projection
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First-Angle Projection
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Reference arrows layout
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Mirrored Orthographic Representation
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Identifying Symbols
To indicate the method of representation
The preferred location is in the lower right-handcorner of the drawing, adjacent to the title block
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Coordinate Input
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Parallel Surfaces and Visible
Edges and Lines
Types of surfaces generally found on
objects can be divided into flat surfaces
parallel to the viewing planes, with orwithout hidden features
Flat surfaces that appear inclined in oneplane and parallel to the other two
principal reference planes
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Hidden Surfaces and Edges
Most engineering drawings are complicatedand many features cannot be seen when viewedfrom outside the piece
It consist of short, evenly spaced dashes
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Application of Hidden Lines
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EXERCISES
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Inclined Surfaces
If the surfaces of an object lie in either a horizontal
or a vertical position, the surfaces appear in their
true shapes in one of the three views and theyappear as lines in the other two views
When a surface is inclined in only one direction, that
surface cannot be seen in its true shape in the top,
front, or side view. In two views it is a distorted
surface; in the third, it appears as a line
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Inclined surfaces
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Circular Features
The circular features appear circular in one view only and
that no line is used to show where a curved surface joins a flat
surfaceHidden circles, like hidden flat surfaces, are represented on
drawings by hidden lines equal to their diameters
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Oblique Surfaces
When a surface is sloped so that it is notperpendicular to any of the three viewing planes, itappears as a surface in all three views but never inits true shape
Since the oblique surface is not perpendicular tothe viewing planes, it cannot be parallel to themand consequently appears foreshortened
The location of some corners of oblique surfacesare found by projecting points and lines from otherviews
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