Vocabulary Terms
- PERSPECTIVE
- OBLIQUE DRAWING
- ISOMETRIC DRAWING
- ONE-VIEW DRAWING
- TWO-VIEW DRAWING
- ORTHOGRAPHIC PROJECTION
- HIDDEN SURFACES
- CURVED SURFACES
- INCLINED SURFACES
Now that you have learned about the kinds of lines found on prints, the next step is to develop your visualization abilities. The ability to ”see” technical drawings; that is to ”think in three dimensions,” is the most important part of this course. Since most engineering and architectural prints utilize some form of orthographic projection (multi-view drawing), that type of drawing will be emphasized.
Before going into a study of orthographic projection, you should be able to recognize several other types of drawings. They are; 1. Perspective drawing, 2. Oblique drawing, and 3. Isometric drawing. As a group, they are called “pictorial drawings”. They are found on prints and are easy to visualize, so let’s look at their differences.
Perspective
Perspective is the most realistic form of drawing. Artists use one-point perspective, two-point (shown here), and three point to create visual depth. Perspectives are used by architects and for industrial pictorials of plan layouts, machinery, and other subjects where realism is required. Objects drawn in perspective grow smaller as they recede into the horizon.
Oblique
Oblique drawings are drawn with one plane (front) of the object parallel to the drawing surface. The side, or other visible part of the object is generally drawn at 30◦ or 45◦. Note that only the side is on an angle. Many times these types of drawing are not drawn to scale. The receding lines are drawn at 45◦ or 30◦ and will be drawn at a different scale as the vertical and horizontal lines. This make the drawing seem “out of shape”. This type of drawing is not used very often in industry.
Isometric
Isometric drawings have less distortion than oblique drawings, and are used more frequently by industry for that reason. An isometric drawing has both visible surfaces drawn at 30◦. These are the most used type of drawings in the piping industry and take a good deal of practice to fully understand how to draw. They best represent what is being built and what it will look like from the different sides with one drawing.
Questions
Directions: Name the types of drawings. Check your own answers.
Single View
A single view of an object is sometimes all that is needed for a complete visual explanation. When dimensions, material, and other information is Included, an object requiring only a single view is easy to understand.
Most one-view drawings are of flat objects, made from materials such as sheet metal and gasket stock. Spherical objects, such as a cannonball, would require only one view and a note indicating the material and diameter of the sphere.
The object shown in the one-view drawing below could be made of any appropriate material that might be specified. In appearance, it is much like the gasket used as part of the cooling system on many cars. All that woul