1. PDT176 COMPUTER-AIDED DRAFTING CHAPTER 5 ISOMETRIC DRAWING

2. CONTENT
Axonometric Drawings
Isometric Projections
Isometric Sketching

3. 5.1 Axonometric Drawings 1) Introduction
Axonometric projection is a parallel projection technique used to create a pictorial drawing of an object by rotating the object on an axis relative to a projection.

4. 5.1 Axonometric Drawings
Introduction (cont.)

5. None of angles are equal.
5.1 Axonometric Drawings
2) Axonometric Drawing Classification
(a) Trimetric
(b) Dimetric
(c) Isometric
None of angles are equal.
Two angles are equal.
All angles are equal.

6. 5.2 Isometric Projections
Rotate 45
about vertical axis
Tilt forward (35o16’)
1) Theory of Isometric Projection
The object is rotated 45 degrees about one axis and 35 degrees 16 minutes on another axis.

7. Isometric Projection:
5.2 Isometric Projections
2) Isometric Projection vs. Isometric Drawing
Isometric Projection:
A view produced using a scale of 0.8.
Isometric Drawing:
A view produced using full scale.

8. Reverse Axis Isometric from the right (or left)
5.2 Isometric Projections
3) Isometric Drawings
An isometric drawing is an axonometric pictorial drawing for which the angle between each axis equals 120 degrees and the scale used is full scale.
Isometric axes can be arbitrarily positioned to create different views of a single object.
Regular Isometric
Reverse Axis Isometric
Long Axis Isometric
View point is looking
down on the top of
the object.
View point is looking
up on the bottom of
the object.
View point is looking
from the right (or left)
of the object.

9. 5.2 Isometric Projections
Isometric Drawings (cont.)
True-length distances are shown along isometric lines.
Isometric line is the line that run parallel to any of the isometric axes.
Nonisometric lines is the inclined and oblique lines and cannot be measured directly.
Isometric lines
Nonisometric lines
Isometric axes

10. 5.2 Isometric Projections
Isometric Drawings (cont.)
Center
lines
Hidden lines
Hidden Lines:
Are omitted unless they are absolutely necessary to completely describe the object.
Center Lines:
Are drawn only for showing symmetry or for dimensioning.

11. 5.3 Isometric Sketching 1) Boxing-In Method (Normal Surfaces) Step 1
Draw the isometric axes.
Step 2
Create the front isometric plane using W and H dimensions.
Multiview Projection

12. 5.3 Isometric Sketching Boxing-In Method (Normal Surfaces) (cont.)
Step 3
Create the top isometric plane using W and D dimensions.
Step 4
Create the right side isometric plane using D and H dimensions.
Step 5
Transfer some distances for the various features from the multiview drawing to the isometric rectangle.

13. 5.3 Isometric Sketching Boxing-In Method (Normal Surfaces) (cont.)
Step 6
Transfer the remaining features from the multiview drawing to the isometric drawing.
Step 7
Darken all visible lines, and erase or lighten the construction lines.

14. Example 5.1
The following figure shows the top, front and right-side views of a part in Third Angle Projection. Draw an isometric view of the part in full scale. You must decide the most suitable view as the frontal plane of the isometric drawing. All dimensions are shown in millimeters (mm).

15. Example 5.1

16. 5.3 Isometric Sketching 2) Nonisometric Lines Step 1
Draw the isometric axes.
Step 2
Create the front isometric plane using W and H dimensions.

17. 5.3 Isometric Sketching Nonisometric Lines (cont.) Step 3
Create the top isometric plane using W and D dimensions.
Step 4
Create the right side isometric plane using D and H dimensions.
Step 5
Transfer the distances for C and A to the top and right side isometric rectangles. Draw line 1 – 2. A C

18. 5.3 Isometric Sketching Nonisometric Lines (cont.) Step 6
Mark off the distance B, and locating points 4 and 3. Connect point 4 – 3.
Step 7
Connect points 1 – 4 and 2 – 3 to draw the nonisometric lines.

19. Example 5.2
The following figure shows the top, front and right-side views of a part in Third Angle Projection. Draw an isometric view of the part in full scale. You must decide the most suitable view as the frontal plane of the isometric drawing. All dimensions are shown in millimeters (mm).

20. Example 5.2

21. 5.3 Isometric Sketching 3) Oblique Planes Step 1
Draw the isometric axes.
Step 2
Create the front isometric plane.

22. 5.3 Isometric Sketching Oblique Planes (cont.) Step 3
Create the top isometric plane.
Step 4
Create the right side isometric plane.
Step 5
Locate the slot across the top plane.

23. 5.3 Isometric Sketching Oblique Planes (cont.) Step 6 Step 7 Step 8
Locate the endpoints of the oblique plane in the top plane by locating distances A, B, C and D. Locate distance H in the front plane and distance I in the profile plane. Connect all respected lines.
Step 7
Draw a line from point 4 parallel to line 7 – 8. Draw a line from point 1 parallel to line 5 – 6.
Step 8
Darken all lines.

24. 5.3 Isometric Sketching 4) Angles Step 1 Draw the isometric axes.
Create the front, top and right isometric plane.
Multiview Projection

25. 5.3 Isometric Sketching Angles (cont.) Step 3
Determine dimensions X and Y. Project both dimensions to create point Z (intersection point).
Step 4
Draw lines from point Z to the upper corners in the front plane. Repeat the same step for the back plane to complete the drawing.

26. 5.3 Isometric Sketching 5) Ellipses
In isometric drawing, a circle appears as an ellipse.
The minor diameter of the ellipses always coincides with the axis of the cylinder, and the major diameter of the ellipse is always at right angles to the minor diameter.
There are three methods to draw isometric ellipses;
True ellipse construction.
Approximate four-center ellipse construction.
Isometric ellipse templates.

27. 5.3 Isometric Sketching
5b) Approximate Four-Center Ellipse Construction
Step 1
Construct an isometric equilateral parallelogram (sides equal) to the diameter of the circle.
Step 2
Find the midpoint of each side of the parallelogram. From that, draw a line to the closest endpoint of the opposite side.
Multiview Projection

28. 5.3 Isometric Sketching
Approximate Four-Center Ellipse Construction (cont.)
Step 3
Draw two small arcs with radius r (centers: A and B). Then, draw two large arcs with radius R (centers: C and D).
Step 4
Draw isometric box. Project arc center points A’, B’ and C’.
Step 5
Construct the isometric ellipse on the rear face. Add tangent lines.

29. 5.3 Isometric Sketching 6) Arcs Step 1 Step 2 Step 3 Multiview Drawing
Construct isometric box. Draw the parallelogram with the sides equal to the diameter of the arc.
Step 2
Construct the bisector. Then, construct the isometric half-circle.
Step 3
Project center points 1 and 2 to a distance equal to the thickness (T) of the object.
Multiview
Drawing

30. Example 5.3
The following figure shows the top, front and right-side views of a part in Third Angle Projection. Draw an isometric view of the part in full scale. You must decide the most suitable view as the frontal plane of the isometric drawing. All dimensions are shown in millimeters (mm).

31. Example 5.3