Orthographic Projection: A Guide to Technical Drawings, Study Guides, Projects, Research of Visual Sociology

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ORTHOGRAPHIC

PROJECTION

C H A P T E R S I X

OBJECTIVES

1. Recognize and sketch the symbol for third-angle projection.
2. List the six principal views of projection.
3. Sketch the top, front, and right-side views of an object with normal, inclined, and oblique surfaces.
4. Understand which views show depth in a drawing showing top, front, and right-side views.
5. Know the meaning of normal, inclined, and oblique surfaces.
6. Compare using a 2D CAD program with sketching on a sheet of paper.
7. List the dimensions that transfer between top, front, and right-side views.
8. Transfer depth between the top and right-side views.
9. Label points where surfaces intersect.
10. Select a good arrangement of generated 2D drawing views to place from a 3D model.

Views of Objects

The system of views is called multiview projection. Each view provides certain definite information. For example, a front view shows the true shape and size of surfaces that are parallel to the front of the object.

Multiview Projection

The system of views is called multiview projection. Each view provides certain definite information.

Revolving the Object to Produce Views

Revolving the Object to Produce Views. You can experience

different views by revolving an object.

Principal Dimensions

The three principal dimensions of an object are width, height, and depth.

The front view shows only the height and width of the object and not the depth. In fact, any principal view of a 3D object shows only two of the three principal dimensions; the third is found in an adjacent view. Height is shown in the rear, left-side, front, and right-side views. Width is shown in the rear, top, front, and bottom views. Depth is shown in the left-side, top, right-side, and bottom views.

Horizontal and Profile Projection Planes

Specific names are given to the planes of projection. The front view is projected to the frontal plane. The top view is projected to the horizontal plane. The side view is projected to the profile plane.

The Glass Box

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

If planes of projection were placed parallel to each principal face of the object, they would form a box.

The Glass Box Unfolded

Lines extend around the glass box from one view to another on the planes of projection. These are the projectors from a point in one view to the same point in another view.

The Orthographic Projection

The front, top, and right-side views of the object shown now without the folding lines.

Necessary Views

The top, front, and right-side views, arranged together, are called the three regular views because they are the views most frequently used.

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

Choice of Views to Fit Paper

Many objects need only two views to clearly describe their shape. If an object requires only two views, and the left-side and right-side views show the object equally well, use the right-side view.

Choice of Front View

The view chosen for the front view in this case is the side, not the front , of the automobile.

Third-Angle Projection

To understand the two systems, think of the vertical and horizontal planes of projection, as indefinite in extent and intersecting at 90° with each other; the four angles produced are called the first, second, third, and fourth angles (similar to naming quadrants on a graph.) If the object to be drawn is placed below the horizontal plane and behind the vertical plane, as in the glass box you saw earlier, the object is said to be in the third angle. In third-angle projection, the views are produced as if the observer is outside, looking in.