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03 October 2003
Mechanical Drawing the Old-Fashioned Way: Different Kinds of Lines
by Brian Mansfield
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Figure 1: The part. Click image to enlarge. |
In the previous article, we discussed drawing views of a part. We also talked about the orthographic projection drawing and its views. Many times, just drawing the lines that are visible in a particular view does not capture all of the features of a part. Some of these features could be hidden, and drawing these hidden lines as visible solid lines will lead to confusion. To get around this problem, it is pretty standard to show lines that are hidden as dashed lines with the same thickness of the visible lines. So for instance, if we were to draw a front, top and right side of the part in Figure 1, the views of just the visible lines would look like Figure 2. Notice some of the features are obscured in some of the views. Figure 3 shows the part with the visible lines and the hidden lines.
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Figure 2: Orthographic Projection of the visible lines of the part . Click image to enlarge. |
Figure 3: Orthographic Projection of the visible and hidden lines of the part. Click image to enlarge.
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It is also standard to create what are called centerlines representing circle centers and cylindrical and conical surfaces. These lines are thinner than the lines used for visible and hidden lines, and are represented by a long dash followed by a short dash followed by a long dash…Such as seen in Figure 4. Figure 5 shows these lines in action. These lines are great because not only do they remove ambiguity, but they can also be used for dimensioning which is the topic of the next article in this series. Figure 6 is a preview of how we can use centerlines in dimensioning.
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Figure 4: Useful types of lines. Click image to enlarge. |
Figure 5: Centerlines on the orthographic projection. Click image to enlarge. |
Figure 6: Dimensioning centerlines [Dimensioning.jpg]
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Figure 6: Dimensioning centerlines. Click image to enlarge. |
In your drawing, you should try to make all of the types of lines uniform. For instance, all of the hidden lines should be the same thickness with the same length used for the dashes and spaces. Likewise the centerlines should be consistent throughout the drawing.
There are many more types of lines that we use in mechanical drawing. We will discuss most of them when it is apropos.
Next up: Dimensioning
Homework: Find simple things
around your home and try to create drawings of them.