This document provides information about engineering graphics and different types of technical drawings including isometric projections, oblique projections, and orthographic projections. It includes examples of how to draw boxes, circles, cylinders, and other objects in isometric and oblique views using techniques like the box method. Guidelines are provided for placement of objects, dimension lines, and treatment of curves and angles in different types of projections. Examples are given for drawing objects in cavalier and cabinet views.
8. Circles
• Circles appear as ellipses when
drawn in an isometric sketch.
• Center of any arc lies on a line
perpendicular to the tangent
from the point of tangency.
• Four Center Method or Box
Method may be used to draw
isometric views of circles.
Isometric Drawing II 8
9. Circles in Isometric View
Orthographic View Isometric View
Isometric Drawing II 9
10. Circles in Isometric View
Orthographic View Isometric View
Ellipse by four center method
Isometric Drawing II 10
12. Curves in Isometric Views
• Circular or other curves will not show in its true shape when
drawn in isometric views.
• Any curve can be drawn by plotting points on it from isometric
reference lines (co-ordinates) that are parallel to isometric
axes
Isometric Drawing II
12
18. Arcs in Isometric Sketches
• Arcs are usually sketched by:
– Locating their centers
– Boxing the arc in the enclosing parallelogram, which is
drawn along isometric lines.
– Sketch the arc tangent to the enclosing box.
Isometric Drawing II 18
19. Circle on a Non-isometric Plane
1
1 1
Locate the center of the circle.
Point 1 coordinates? 2, 4, 3
20. 1
Circle on a Non-isometric Plane
1
1 1
Locate the center of the circle.
Locate the ends of conjugate diameters and
use the parallelogram method to construct
the ellipse in isometric view.
21. Center Lines
• Drawn only for showing symmetry
or dimensioning.
• Often not shown when
communicating with non-technical
people and for non-engineering
purposes.
Isometric Drawing II 21
22. Dimension Lines
• Dimension lines, extension lines
and lines being dimensioned
should lie in the same isometric
plane.
• All dimensions and notes to be
located outside the view
whenever possible.
Isometric Drawing II 22
23. Angles
• Angles must be laid off with coordinates which are
parallel to isometric axes.
– Convert angles of orthographic projection to coordinates at same
scale as of Isometric.
Isometric Drawing II 23
1200
600
600
1200
a
b
c
900
900
900
300 600
a b
c
24. Offset Method
• Used for objects with no well-defined isometric
planes, i.e. neither non-isometric lines or their ends
lie in isometric planes.
• Perpendiculars are dropped from each end of the
edge to horizontal or vertical reference plane
(isometric planes).
• The point of intersections are located to trace the
actual location.
Isometric Drawing II 24
29. Plane of
projection
Oblique Projection
• Plane of projection is parallel
to one of the principal planes
of the object.
• Projection lines are parallel,
but NOT perpendicular to the
plane of projection.
• Object not tilted as done in
isometric projection.
• Distances 1-2, 1-3 do not
change due to projection.
• However, distance 1-4 can
Oblique Projection 29
2
4
3
1
30. • Features in the frontal plane (circles, etc.) do not get
distorted.
• Distortion limited to 3rd dimension.
• Two types of oblique projections: Cavalier, Cabinet.
Oblique Projection
31. More About Oblique Projections
• Two axes (width, and height) are mutually perpendicular.
• Third axis (depth) is usually at 30o or 45o from the horizontal.
• Width and height dimensions are at 1:1 scale.
• Depth ratio: 1:1 for Cavalier and 1:2 for Cabinet.
32. Which Object Looks More Like a Cube?
Depth dimension appears more than what it actually is.
Oblique Projection 32
34. Isometric versus Oblique Projections
Isometric
Projectors are perpendicular to
plane of projection.
Angle between three axes is
equal.
Depth is 81% of actual.
Shapes will be distorted.
Oblique
Projectors are oblique to the
plane of projection.
Two axes are mutually
orthogonal. The depth axis is
at 30o or 45o to the horizontal.
Depth is 100% in Cavalier and
50% in Cabinet of the original.
Shapes are not distorted in the
plane parallel to object-face.
41. 1. Draw a rectangle: overall width and height of the object.
2. Generate parallel lines from each corner of the box backwards
in depth direction at 30o or 45o to the horizontal.
3. Mark extension lines at points equaling the object’s depth.
4. Connect the depth-lines to form a box.
5. Add any details such as holes, notches, onto the front view
6. Extend the details in the depth direction of the object.
7. Complete the sketch by darkening in the object lines.
Step-by-Step Approach
41
