1. TECHNICAL SKETCHING
C H A P T E R T H R E E

2. OBJECTIVES
After studying the material in this chapter, you should be able to:
1. Define the terms vertex, edge, plane, surface, and solid.
2. Identify four types of surfaces.
3. Identify five regular solids.
4. Draw points, lines, angled lines, arcs, circles, and ellipses.
5. Apply techniques that aid in creating legible well-proportioned
freehand sketches.
6. Apply techniques to draw irregular curves.
7. Create a single-view sketch.
8. Create an oblique sketch.
9. Create perspective sketches.
10. Create an isometric sketch of an object.
Shaded Sketch Showing Details of Wire Placement. (Courtesy of Quantum Design.)

3. UNDERSTANDING SOLID OBJECTS
Three-dimensional figures are referred
to as solids. Solids are bounded by
the surfaces that contain them. These
surfaces can be one of the following four
types:
• Planar
• Single curved
• Double curved
• Warped
Regardless of how complex a solid may be, it is composed of combinations of these basic types of surfaces.

4. UNDERSTANDING SKETCHING TECHNIQUES
Look for the essential shapes of objects
And use construction lines
break down complex shapes into simpler geometric
primitives

5. SKETCHING TECHNIQUES
The contours of an object are the main outlines that separate it from the surrounding space. One way to think about the contours of objects is to look at the contrast between the positive and negative space. Positive space is the space occupied by the object. Negative space is the unoccupied space around it.

6. Viewpoint and Shading
As you sketch objects, keep in mind that you want to maintain a consistent viewpoint, like a camera does.
Adding shading to your sketch can give it a more realistic appearance because it represents the way the actual object would reflect
light.
Hatching and stippling

7. Edges and Vertices Edges Vertices Points and Lines
An edge of the solid is formed where two surfaces intersect. Edges are represented in drawings by visible or hidden lines.
Vertices
A vertex (plural, vertices) of a solid is formed where three or more surfaces intersect..
Points and Lines
A point is used to represent a location in space but has no width, height, or depth.

8. Points and Lines
A point is used to represent a location in space but has no width, height, or depth.
A line is used in drawings to represent the edge of a solid
object.

9. Angles
An angle is formed by two intersecting lines. A common symbol for angle is
Showing Angles

10. Drawings and Sketches
The following are important skills to keep in mind for sketches
and drawings:
Accuracy. No drawing is useful unless it shows the information
correctly.
2. Speed. Time is money in industry. Work smarter and learn
to use techniques to speed up your sketching and CAD
drawings while still producing neat accurate results.
3. Legibility. A drawing is a means of communicating with
others, so it must be clear and legible. Give attention to details.
Things that may seem picky and small as you are
drawing may be significant and save money or even lives
when the product is built.
4. Neatness. If a drawing is to be accurate and legible, it must
also be clean.

11. Freehand Sketching
Freehand sketches are a helpful way to organize your thoughts and record ideas. They provide a quick, low-cost way to explore various solutions to design problems so that the best choices can
be made.

12. TECHNIQUE OF LINES line patterns
The chief difference between a drawing and a freehand sketch lies in the character or technique of the lines.
A good freehand line is not expected to be as rigidly straight or exactly uniform. A good freehand line shows freedom and variety, whereas a line drawn using CAD or instruments should be exact.
line patterns

13. Lineweights
Even in freehand drawings, thick lines should be twice the width of thin lines.
Thicknesses do not have to be exact, but there should be an obvious difference between thick and thin lines. Because visible lines and cutting-plane lines are the two thick line patterns, other lines should be distinctly
thinner in comparison.
To draw thick and thin lines freehand,
you might like to keep two pencils
handy, one that is razor sharp for thin
lines and another that is dulled, to
create thicker lines. As the sharp point
becomes dulled, switch it with the
dull pencil, and sharpen the other,
so that there is always one sharp
and one dulled point ready to use.

14. SKETCHING STRAIGHT LINES
Most of the lines in an average sketch are straight lines. With
practice, your straight lines will naturally improve, but these
basics may help you improve quickly.
• Hold your pencil naturally, about 1" back from the point,
and approximately at a right angle to the line to be drawn.
• Draw horizontal lines from left to right with a free and
easy wrist and arm movement.
• Draw vertical lines downward with finger and wrist
movements.

15. MAINTAINING PROPORTIONS
The most important rule in freehand sketching is to keep the sketch in
proportion, which means to accurately represent the size and position of each part in relation to the whole.
To maintain proportions, first determine the relative proportions of height to width and lightly block them in. You can mark a unit on the edge of a strip of paper or use your pencil to gauge how many units wide and high the object is.

16. ONE-VIEW DRAWINGS
Frequently, a single view supplemented by notes and dimensions
is enough information to describe the shape of a relatively
simple object.
Note how thickness of the material is given as “0.25 BRASS” So, an additional
view is not needed to dimensionally give the material thickness.

17. PICTORIAL SKETCHING
A pictorial sketch represents a 3D object on a 2D sheet of paper
by orienting the object so you can see its width, height, and depth in a single view.

18. AXONOMETRIC DRAWINGS Axonometric
Various types of pictorial drawings are used extensively in catalogs,
sales literature, and technical work. They are often used in patent drawings; in piping diagrams; in machine, structural, architectural design, and in furniture design; and for ideation sketching.
Axonometric
(Courtesy of Douglas Wintin.)

19. Projection Methods The four principal types of projections:
a Multiview
b Axonometric
c Oblique
d Perspective

20. ISOMETRIC DRAWINGS steps…

21. OBLIQUE SKETCHING steps…

22. SHADING
Shading can make it easier to visualize pictorial drawings, such as display drawings, patent drawings, and catalog drawings.
Ordinary multiview and assembly drawings are not shaded.
Methods of Shading