2.2 Orthographic Projection
To see all the dimensions, holes, depressions, spaces, curves, and angles in an object, you may need to view it from various sides. In a drawing, all these sides and views must be shown, however, on a flat sheet of drawing material. To make these multiple views possible in a flat plane, the orthographic projection method of drawing was developed. Orthographic projection is a two-dimensional representation of a three-dimensional object and is also known as multiview projection.
To make an orthographic drawing, the object to be drawn is imagined as being located and viewed inside a clear glass box. Each side of this imaginary clear box consists of what is known as the projection plane. See Figure 2-1. All points and lines are imagined as projected onto the six sides of the box, just as they would be seen by a person viewing the object through each of the projection planes. The object is then drawn on the various projection planes, Figure 2-2. Note that the lines of sight from the object to the projection plane are parallel to each other, Figure 2-3. This is what is known as parallel projection and it is the projection type of choice for making working drawings. When the sides of the clear box are folded out until they are flat, all sides of the object can be seen in one flat plane and drawn on a single print. See Figure 2-4.
To make an orthographic drawing, the object to be drawn is imagined as being located and viewed inside a clear glass box. Each side of this imaginary clear box consists of what is known as the projection plane. See Figure 2-1. All points and lines are imagined as projected onto the six sides of the box, just as they would be seen by a person viewing the object through each of the projection planes. The object is then drawn on the various projection planes, Figure 2-2. Note that the lines of sight from the object to the projection plane are parallel to each other, Figure 2-3. This is what is known as parallel projection and it is the projection type of choice for making working drawings. When the sides of the clear box are folded out until they are flat, all sides of the object can be seen in one flat plane and drawn on a single print. See Figure 2-4.
2.2.1 Views
When discussing orthographic drawings, the direction from which the object is viewed is given a name. Generally, the view that shows the most about the overall shape of the object is called the front view. The view to the right of the front view (as the orthographic box is unfolded in your imagination), is known as the right side view. The view to the left of the front view is the left side view. The view above the front view is called the top view and the view below the front view is the bottom view. See Figure 2-2. A back view is possible on an orthographic drawing, but it is very seldom used. The back view can also be referred to as the rear view.
To produce an accurate drawing of an object, it is seldom necessary to show all six views. A working drawing typically shows three views of an object, which is sufficient to describe its shape and give all the required dimensions.
When discussing orthographic drawings, the direction from which the object is viewed is given a name. Generally, the view that shows the most about the overall shape of the object is called the front view. The view to the right of the front view (as the orthographic box is unfolded in your imagination), is known as the right side view. The view to the left of the front view is the left side view. The view above the front view is called the top view and the view below the front view is the bottom view. See Figure 2-2. A back view is possible on an orthographic drawing, but it is very seldom used. The back view can also be referred to as the rear view.
To produce an accurate drawing of an object, it is seldom necessary to show all six views. A working drawing typically shows three views of an object, which is sufficient to describe its shape and give all the required dimensions.