FREEHAND SKETCHING-I FREEHAND SKETCHING-

1. FREEHAND SKETCHING-I

2. Communicating Technical Designs
 Sketching and Shape Description
 Straight Lines
 Circles and Arcs
 Proportions
 Generating Technical Designs

3. Purpose
 The main purpose of sketching is to convey ideas.
 Engineers have to use sketches to brainstorm ideas,
as well as, to show others what they are working on
or what should be designed.
 Sketches are also used to document measurements
from the field before they are produced as solid
models on the computer.

4. Freehand Sketching
 Most original designs are first expressed on medium
as a freehand sketch.
 Used for:
 Amplifying and clarifying
 Recording verbal explanations

5. Technical Sketching
 Engineers’ view: ability to render serviceable
sketches greater value than skill to create instrument
drawings.
 Freehand sketch should not mean crude and
sloppy.
 Freehand sketch should be made with care and
attention to proportion, clarity, and line widths.

6. Types of Sketches

7. Scale
 Typically not made to any scale.
 Correct proportions are needed.
 Size of sketch:
 Optional
 Determined by:
 Complexity of object
 Size of paper
 Small objects may be enlarged to show details
clearly.

8. Purpose
 Proper documentation in a notebook is essential.
 When proper documentation is made, ideas are not
lost and projects can be duplicated.
 The sketch on the next slide is a sample from a
notebook where a sketch was made and notes as
well as dimensions have been documented.

9. Proposed Notebook Sample
Shows design details
Size requirements.
Initialed and dated.
Title

10. Freehand Sketching
 Freehand sketching is a method of making a drawing
without the use of instruments.
 Most designers use sketches to “think through” an idea
before making the final drawing.
 Freehand sketching requires only a pencil and plain or
grid paper.

11. Freehand Sketching
 Cross-section paper may be used for freehand
sketching.

12. Sketching Technique
 When sketching, hold the pencil with a grip firm
enough to control the strokes.
 Your arm and hand should have a free and easy
movement.
 As you sketch, rotate the pencil slightly between
the strokes to retain the point longer.
 Initial lines should be sharp and light.

13. Sketching Technique
 Apply light pressure to avoid making grooves in
the paper.
 Keep your eye on the point where the line will
end; use a series of short strokes to reach that
point.
 When all the lines are sketched, go back and
darken the lines.
 Strive for neatness and good technique.

14. Sketching Technique
 When sketching, grip your the pencil farther back
than you normally would.

15. Sketching Horizontal Lines
 There are four basic steps.

16. Sketching Vertical Lines
 There are four basic steps.
16

17. Sketching Inclined Lines
 Locate the end points of the
line.
 Position arm for trial
movement.
 Sketch several short, light
lines.
 Focus on end point.
 Darken the line.

18. Sketching an Angle
 First, sketch a right
angle (90°).
 Subdivide the right
angle to get the
angle you desire.

19. Sketching Techniques
 Line Types:
Vertical Line
Horizontal Line
Inclined Line

20. Sketching Techniques
 Finding the slope angle of an inclined line:
Run = 4
Rise = 2

 27
s
Note: Rise and Run units
do not matter (As long as the
units are the same). You are
finding an angle. In the above
case, we are counting grid boxes.
Equation:
tans = RISE/RUN
tans = 2/4
tans = .5
s = arctan .5

21. Sketching Techniques
 Sketching a Line.

22. Sketching Techniques
 Sketching an Arc

23. Sketching Techniques
 Sketching a Circle
1) Setup the
diameter
2) Square in the
diameter
3) Sketch
diagonals

24. Sketching Circles and Arcs
 There are several methods of sketching circles and
arcs:
 Centerline method.
 Enclosing square method.
 Hand-pivot method.
 Free-circle method.
 All are sufficiently accurate, so use the best method
for a particular situation.

25. Centerline Method
 Locate centerlines.
 Mark off radius.
 Position arm.
 Sketch the circle in short sweeps.
 Darken the circle.

26. Enclosing Square Method
 Locate centerlines.
 Sketch a box equal to the diameter.
 Sketch arcs where the centerlines cross
the box line.
 Sketch the circle.

27. Sketching Techniques
 Sketching an Arc

28. Sketching Techniques
 Sketching a Circle
4) Identify triangle
centers
5) Sketch arcs

29. Hand-Pivot Method
 First, position the pencil and small finger. Then,
rotate the paper to sketch the circle.

30. Sketching Ellipses
 The rectangular method for sketching ellipses is
similar to the enclosing square method for circles.

31. Sketching Irregular Curves
 Sketch an irregular curve by connecting a series
of points at intervals of 1/4" to 1/2" along its path.

32. Proportion in Sketching
 Proportion is the size relationship of one part to
another or to the whole object.
 Keep the same width, height, and depth in
proportion.
 Unit method.
 Pencil-sight method.

33. Proportion in Sketching
 Gauge proportions using the pencil-sight method.

34. Size and Proportion
 Although you have learned to draw lines and arcs, you can not
communicate properly until you understand how to sketch with
the correct size and proportion. Without proper size and
proportion your sketch will not look right.
 Size: Length, width, height, distance. How big is the object you
are sketching?
 Proportion: If two objects are five feet apart in real life, then
those two objects must appear to be five feet apart in your
sketch.

35. Size and Proportion
 How to create proper size and proportion.
Technique I
 Using a pencil to measure.
Figure 2
Hold your pencil at arms
length as you see in Figure 2.
Use the top of the pencil and
your thumb as a distance for
the height of the window. This
distance will be used as a
reference for sketching the rest
of the house as we did in the
house on the next slide.

36. Size and Proportion
 How to create proper size and proportion.
Technique I
 Using a pencil to measure.
Figure 3
As you see in the completed
house in Figure 3, the units
of the numbered dimensions
are in windows.
You should also notice that
the use of graph paper also
helps in creating proper size
and proportion.

37. Size and Proportion
 How to create proper size and proportion.
Technique II
 Boxing in the sketch.
In Figure 4 we are sketching
a chair. We sketch the boxes
to the largest outside
dimensions of our final
object. Notice that light
construction lines are also
used to help guide us to
the proper size and
proportion.
Figure 4

38. Size and Proportion
 How to create proper size and proportion.
Technique II
 Boxing in the sketch.
Finally we use our sketching
techniques for drawing arcs,
lines and circles to complete
our chair in Figure 5.
Notice the box we started
with is still existent as light
construction lines. These are
our guides for proportion and
size.
Figure 5

39. Alphabet of Lines

40. Border Lines
 Border lines are very heavy lines used to form a
boundary for the drawing.

41. Object Lines
 Object lines are heavy lines that outline features
of an object.

42. Hidden Lines
 Hidden lines represent edges that are behind a
visible surface in a given view.

43. Centerlines
 Centerlines indicate the center of holes and
symmetrical objects, such as windows and doors.

44. Extension Lines
 Extension lines are used to denote the
termination points of a dimension line.
Extension lines

45. Dimension Lines
 Dimension lines are used to show size and
location. They have a dimension figure halfway
between the ends of the dimension line.

46. Long Break Lines
 Long break lines are used to show that not all of
the part is shown.

47. Short Break Lines
 Short break lines show part of the object broken
away.

48. Cutting-Plane Lines
 Cutting-plane lines are used to show where the
object is sectioned.

49. Section (Crosshatch) Lines
 Section lines or crosshatch lines are used to show
that a feature is sectioned.
 May represent different types of material.

50. Alphabet of Lines
Object Line: Thick lines
about .6mm(.032in) that
show the visible edges of
an object.
Hidden Line: Lines used to
show interior detail that is not visible
from the outside of the part.
Center Line: Lines that define
the center of arcs, circles, or symmetrical parts.
They are half as thick as an object line.
Construction Line: Very lightly
drawn lines used as guides to help draw
all other lines and shapes properly.
Usually erased after being used.
Short Break Line: A freehand
drawn line that shows where a part is
broken to reveal detail behind the part or
to shorten a long continuous part. (See
example of Long Break Line
on the next slide.)
Section Lines: Lines are used to
define where there is material
after a part of the object is cut away.