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Orthographic Projection. Objectives. List the six principal views of projection Sketch the top, front and right-side views of an object with normal, inclined, and oblique surfaces. Objectives (cont.). Understand which views show depth in a drawing that shows top, front, and right-side views

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Orthographic Projection

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Orthographic projection l.jpg

Orthographic Projection


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Objectives

  • List the six principal views of projection

  • Sketch the top, front and right-side views of an object with normal, inclined, and oblique surfaces


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Objectives (cont.)

  • Understand which views show depth in a drawing that shows top, front, and right-side views

  • Know the meaning of normal, inclined, and oblique surfaces


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Objectives (cont.)

  • Know which dimensions transfer between top, front, and right-side views

  • Transfer the depth between the top and right-side views

  • Label points where surfaces intersect


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Views of Objects

  • Drawings are two-dimensional representations of objects that allow you to record sizes and shapes precisely

  • To provide a complete and clear description, the views must be systematically arranged

  • The system of views is called multiview projection


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The Six Standard Views

  • Any object can be viewed from six mutually perpendicular views


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The Six Standard Views

  • These views are called principal views and are arranged in a standard way


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The Six Standard Views

  • The top, front, and bottom views align vertically

  • The rear, left-side, front, and right-side views align horizontally

  • To draw a view out of place is a serious error


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Principal Dimensions

  • The three principal dimensions of an object are:

    • Width

    • Height

    • Depth


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Principal Dimensions

  • Any principal view shows two of the three principal dimensions

  • Height is shown in the rear, left-side, front, and right side

  • Width is shown in the rear, top, front, and bottom

  • Depth is shown in the left-side, top, right-side, and bottom views


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Example


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Projection Method

  • Frontal plane – the plane upon which the frontal view is projected

  • Horizontal plane – the plane upon which the top view is projected

  • Profile plane – the plane upon which the side view is projected


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The Glass Box

  • One way to understand the standard arrangement of views on a sheet of paper is to envision the object in a glass box

  • The outside observer would see six standard views of the object through the sides of this imaginary glass box


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The Glass Box


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Transferring Depth Dimensions

  • The depth dimensions in the top and side views must correspond

    • You may find it convenient to use dividers, a ruler, or a 45-degree miter line to project dimensions


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Necessary Views

  • A sketch or drawing should only contain the views needed to clearly and completely describe the object

    • Choose the views that have the fewest hidden lines and show essential contours or shapes most clearly

    • Complicated objects may require more than three views

    • Some objects only need one or two views


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Necessary Views


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Necessary Views


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Necessary Views


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Orientation of the Front View

  • The front view should:

    • Show a large surface of the part parallel to the front viewing plane

    • Show the shape of the object clearly

    • Show the object in a usual, stable, or operating positions


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Orientation of the Front View

  • When possible, a machine part is drawn in the orientation it occupies in the assembly

  • Usually screws, bolts, shafts, tubes, and other elongated parts are drawn in a horizontal position


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Orientation of the Front View


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First- and Third-Angle Projection

  • There are two main systems used for projecting and unfolding the views:

    • Third-angle projection which is used in the United States, Canada and some other countries

    • First-angle projection which is primarily used in Europe and Asia

  • You should understand both methods


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Third-angle Projection


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First-angle Projection


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Hidden Lines

  • An advantage of orthographic views is that each view shows the object all the way through as if it were transparent

    • Thick dark lines represent visible features

    • Dashed lines represent features that would be hidden behind other surfaces

    • When possible, choose views that show features with visible lines


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Centerlines

  • The centerline is used to:

    • Show the axis of symmetry of a feature or part

    • Indicate a path of motion

    • Show the location for bolt circles or other circular patterns

  • The centerline pattern is composed of three dashes, one long dash on each end with a short dash in the middle


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Centerlines


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Precedence of Lines

  • When lines coincide on a drawing the rules of precedence are:

    • Visible lines always take precedence over hidden or centerlines

    • Hidden lines take precedence over centerlines


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Precedence of Lines


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Visualization

  • Even those with experience can’t always look at a multiview sketch and instantly visualize the object represented

  • You will learn to interpret lines in a logical way in order to visualize the object as a whole


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Views of Surfaces

  • A plane surface that is perpendicular to a plane of projection appears on edge as a straight line

  • If a plane is parallel to the plane of projection, it appears true size

  • If a plane is angled to the plane of projection, it appears foreshortened


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Views of Surfaces


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Views of Surfaces

  • A plane surface always projects either on edge or as a surface in any view

    • It can appear foreshortened, smaller than actual size, but it can never appear larger than its true size in any view


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Normal Surfaces

  • A normal surface is parallel to a plane of projection


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Inclined Surfaces

  • An inclined surface is perpendicular to one plane of projection but inclined to adjacent planes


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Oblique Surfaces

  • An oblique surface is tipped to all principal planes of projection and does not appear true size in any standard view


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Edges

  • The intersection of two plane surfaces of an object produces an edge which shows as a straight line in a drawing

  • If an edge is perpendicular to a plane of projection it appears as a point, otherwise it appears as a line


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Parallel Edges

  • When edges are parallel to one another on an object, they will appear as parallel lines in every view unless they align one behind the other


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Angles

  • If an angle is in a normal plane, it will show true size on the plane of projection to which it is parallel

  • If an angle is in an inclined plane, it may be projected either larger or smaller than the true angle depending on its position


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Angles


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Interpreting Lines

  • A straight, visible, or hidden line in a sketch has three possible meanings:

    • An edge between two surfaces

    • The edge view of a surface

    • The limiting element of a curved surface

  • Since no shading is used on orthographic views, you must examine all views to determine a line’s meaning


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Interpreting Lines


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Similar Shapes of Surfaces

  • If a flat surface is viewed from several different positions, each view will show the same number of sides and vertices and same characteristic shape whenever it appears as a surface

    • This consistency of shapes is useful in analyzing views


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Similar Shapes of Surfaces


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Interpreting Views

  • One method of interpreting sketches is to reverse the mental process used in projecting them

  • Each view provides certain definite information about the shape of the object and all are necessary to visualize it completely


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