2. Objectives
• Discuss the purpose of sketching
and its importance
• Sketch a straight line
• Sketch arcs, circles, and ellipses
• Create an orthographic sketch
4. Purpose of Sketching
• Sketch: freehand drawing used to
describe shape and size of an
object
• Quickly expresses an idea
– May be translated into a finished
drawing
• Often used in place of finished
drawings
5. Purpose of Sketching
(cont’d.)
• Sizes of objects in sketch
proportional to one another
• Details needed to fabricate an
object are added to the sketch
6. Basic Sketching Techniques
• Lines lightly sketched with short
overlapping strokes
– Use pencil with sharp point
• Lines darkened and weighted
according to their purpose
– In same manner as lines on finished
drawing
8. Sketching Arcs, Circles, and
Ellipses
• Sketch an arc by first constructing
a right angle
• Place guide points on the legs of
the angle to mark start and end
points of the arc
9. Sketching Arcs, Circles, and
Ellipses (cont’d.)
• Connect points with a curved line
• Erase unnecessary lines after the
sketch is completed
10. Sketching Arcs, Circles, and
Ellipses (cont’d.)
• Alternative method:
– Draw a right angle
– Place two equidistant points on the
legs of the angle
– Connect the points with a diagonal
line to form a triangle
11. Sketching Arcs, Circles, and
Ellipses (cont’d.)
• Alternative method (cont’d.):
– Place a dot in the middle of the
triangle
– Draw a curved line to connect all
three points
12.
13. Sketching Arcs, Circles, and
Ellipses (cont’d.)
• Sketch arcs that intersect by
combining techniques for drawing
arcs
• Sketch a circle using the same
process for sketching an arc
– Repeat for all quarters of the circle
• Circle may appear as an ellipse
14.
15.
16. Sketching Arcs, Circles, and
Ellipses (cont’d.)
• Sketch an ellipse by laying out a
rectangle with sides equal to major
and minor axes
• Rectangle divided into four equal
quarters
– Dividing lines represent major and
minor axes
17. Sketching Arcs, Circles, and
Ellipses (cont’d.)
• Use triangles or rectangles as
guides
• Use method similar to sketching a
circle
18.
19. Sketching Arcs, Circles, and
Ellipses (cont’d.)
• Oblique or isometric drawings
often used to represent weldments
• Three-dimensional drawings
• Shown alone or in conjunction with
orthographic drawing
20. Oblique Sketching
• Draw orthographic view that best
describes shape and shows most
detail
• Draw parallel receding lines at
about 45 degree angles from the
corners of the view
– Drawn to the right for right oblique
drawing
– Drawn to left for left oblique drawing
21. Oblique Sketching (cont’d.)
• Lines are not usually shown for any
part of the object not visible
• Receding lines extend one-half the
length shown in an orthographic
drawing
• Repeat lines shown on
orthographic view on the terminal
points of receding lines
22. Oblique Sketching (cont’d.)
• Broken lines show hidden edges
• Oblique circles sketched using
oblique cube
– Locate points on a rectangle
– Draw a series of arcs
23.
24.
25. Isometric Sketching
• Isometric graph paper preferable to
develop isometric sketch
– All surfaces shown at 30 degree
angles
• View of object that best shows
shape and detail drawn at 30
degree angle
26. Isometric Sketching (cont’d.)
• Parallel receding lines sketched at
30 degree angles from each corner
– Only visible part of object sketched
• Draw back edges at points that
approximate the size of the object
• Receding lines reduced to two-
thirds of orthographic length
27. Isometric Sketching (cont’d.)
• When surfaces of object lie in
different planes
– Start from front face
– Develop each portion progressively to
back face
• Sketching isometric circles follows
same process as sketching regular
circles
28.
29.
30.
31. Summary
• A sketch is a freehand drawing
used to describe the shape and
size of an object
• Lines are sketched with short
overlapping strokes and then
darkened and weighted
• There are two methods for drawing
arcs, circles and ellipses
