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Chapter Description

In this sample chapter from Engineering Graphics with AutoCAD 2020, author Bethune presents the fundamentals of freehand sketching as applied to technical situations. It includes both two-dimensional and three-dimensional sketching. Like any skill, freehand sketching is best learned by lots of practice.

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Engineering Graphics with AutoCAD 2020

Engineering Graphics with AutoCAD 2020

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4-6 Proportions

Sketches should be proportional. A square should look like a square, and a rectangle like a rectangle. Graph paper is very helpful in sketching proportionally, but it is still sometimes difficult to be accurate even with graph paper. Start by first sketching very lightly and then checking the proportionality of the work. See Figure 4-4. Go back over the lines, making corrections if necessary, and then darken in the lines. The technique of first sketching lightly, checking the proportions, making corrections, and then going over the lines is useful regardless of the type of paper used.

It is often helpful to sketch a light grid background based on the unit values of the object being sketched. This is true even if you are working on graph paper because it helps to emphasize the unit values you need. See Figure 4-5.

The exact proportions of an object are not always known. A simple technique to approximately measure an object is to use the sketching pencil. See Figure 4-6. Hold the pencil at arm’s length and sight the object. Move your thumb up the pencil so that the distance between the end of the pencil and your thumb represents a distance on the object. Transfer the distance to the sketch. Continue taking measurements and transferring them to the sketch until reasonable proportions have been created.

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