| Intermediate Technology Education | Control Technology | Design Stage 2 | Topic 6 | Knowledge/Skill Activity 1 |
Understanding Technical Drawings
Technical drawings are line drawings made according to a set of rules and procedures. The rules and procedures are pretty much standardized throughout the world. Types of lines, how they are placed and where different parts of the drawing are placed enable anyone to read and interpret the drawing and reach the same decisions. In fact, technical drawings are a universal language for communicating technical information.
While there are many types of drawings, and even many types of technical drawings, we are concerned here with two general types of technical drawings
Pictorials are picture drawings that show more than one side of an object at the same time. The most common forms of pictorial drawings are
The following sequence of images illustrates the relationship of one-point perspective to cabinet projections.
The next sequence illustrates the relationship of isometric drawings to two-point perspective.
Isometric drawings are unique in that the edges are drawn vertically or at 30 degrees to the horizontal. As well, isometric drawings generally only use one type of line—a thin solid line—and do not use colour or shading. The image below illustrates that clearly.
Pictorials are drawn when you want to show what something looks like. Here are a few more examples of isometric drawings.
The example below breaks one of the rules for isometric drawings. How does it break the rules?
You may wish to try this interactive isometric drawing tool. It will let you construct simple shapes. It does illustrate the typical grid structure of isometrics.
Orthographic drawings are related to isometric drawings. Isometrics show multiple sides of an object at the same time. Orthographics show individual views of the objects. The next sequence of drawings shows how that relationship works, beginning with labeling of the sides of an object in isometric drawings.
We start with a box, shown as an isometric, and them we label its surfaces. Like all boxes, it has 2 ends, 2 sides, and a top and bottom.
The labels we used are descriptive, but they don't tell us much about their location on the drawing. The next drawing shows what we call a convention. Over time, people on the industry agreed that the labels used in the next drawing would be the accepted ones. That is, regardless of what was in the drawing, the labels would always be the ones in the drawing.
The next drawing shows how the labels are used, regardless of what is in the drawing. You may argue that it does not make sense to call the front of the truck, the Right Side View, and the side of the truck the Front View. The answer is , "we are not". We are labeling the location, not the object. It is very important to keep this in mind.
You may be wondering about the three views that are hidden. They are called the Bottom View, the Left Side View, and the Rear View. Can you determine where they go?
The next drawing shows the relationship of isometric surfaces to the views in orthographic drawings.
The more sophisticated explanation for this relationship focuses on the views as projections of the surfaces. If you have interest in further exploration of this subject, you may wish to check the page Isometric Drawing and Third Angle Projection.
Remember that upside down truck in the isometric above? Here is what it looks like as an orthographic drawing.
Now that you know the relationship between the isometric drawing and the orthographic views of the same object, it may com as no surprise that there how you orient the object in an isometric drawing affects the physical space needed to make the orthographic drawings. The next set of drawings shows the same box, but placed in different directions. Drawing 1 on the left has the long direction along the front view, resulting in a compact drawing for the Orthographics. Drawing 2, on the right, has the long direction along the right side, resulting in a taller set of orthographic drawings. Placing the long direction along the front view is another convention when creating isometric and orthographic drawings.
The next figure shows the convention for technical drawings, when both the Orthographics and Isometrics are on the same sheet. This type of orthographic is called Third Angle Projection, and is widely used in North America. Another type called First Angle Projection is more common in Europe.
As you can see in the next figure, the use of both types of drawing can contribute to understanding what the drawings are describing.
The placement of each drawing in an orthographic has special meaning. The next drawing has labels for each of the drawings. Each drawing is a single view of the object. Views are always placed in the locations shown.
Figure Orthographic Views of an Object
Note that regardless of the object, the views are labelled exactly as shown. The next image shows how the views relate to an isometric drawing of the same thing.
Figure Relationship of Views and Isometric Drawings
Sometimes both types of technical drawing are needed to understand an object's structure, as in the next example.
Figure Sheet Metal Clip Drawings
If you wish more information, check these web pages
When you are ready, go to Your Turn