Theory of Shape Description[1]

8/2/2019 Theory of Shape Description[1]

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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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Documents

Theory of Shape Description[1]