1. CE En 112 Engineering Drawing with CAD Application
Chapter 2: Sketching and Text (Lecture D)
Pictorial Drawings

2. Lecture Outline Objectives Introduction (2.4, p.85)
Isometric drawings (2.4.1, p.87)
Oblique drawings (2.4, p.86)
Perspective drawings (2.7, p.104)
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3. Objectives Learn how to construct three types of pictorial drawings:
1) Isometric
2) Oblique
3) Perspective

4. Introduction
Comparison of Isometric, oblique, and perspective drawings

5. Introduction (con’t)
Examples:
Perspective
Oblique

6. Isometric Drawings (2.4)
An axonometric pictorial drawing for which the angle between axes equals 120 degrees and the scale used is full scale
Isometric axes can be positioned in a number of ways to create different views of the same object
Regular isometric is the most common type

7. Isometric Drawings (con’t)
True length distances can only be measured along isometric lines, that is, lines that run parallel to any of the isometric axes

8. Isometric Drawings (con’t)
Hidden lines are omitted unless absolutely necessary to describe the object
Center lines are drawn for showing symmetry or for dimensioning – normally they are not shown
Example: Hidden Lines Necessary for Details
Example: Center Lines for Dimensioning

9. Isometric Drawings (con’t)
Dimensioning for production purposes:
Dimensions per ANSI standards
Dimension lines, extension lines, and lines dimensioned shall lie in the same plan
All dimensions and notes should be unidirectional, reading from the bottom upward and outside the view

10. Isometric Drawings (con’t)
Dimensioning for illustration purposes:
Use the aligned method
Dimension lines, extension lines, and lettering are all draw in the plane of one of the faces of the object
Takes on more of a pictorial look

11. Isometric Drawings (con’t)
Constructing an isometric drawing using the Boxing-In Method:
Box in from the outmost shape to inside details

12. Isometric Drawings (con’t)
What if you have non-isometric lines?
Remember that true-length distances can only be measured along isometric lines, that is, lines that run parallel to any of the isometric axes

13. Isometric Drawings (con’t)
What if you have curves?
Use the offset coordinate method

14. Oblique Drawings (2.4)
A form of pictorial drawing in which the most descriptive or natural view is treated as the front view and is placed parallel to the plane of projection
Typical oblique drawing angles are 30, 45, or 60 degrees from the horizontal

15. Oblique Drawings (con’t)
Three basic types of oblique drawings:
Cavalier: drawn true length along the receding axis
Cabinet: drawn half the true length along the receding axis
General: drawn anywhere from full to half length along the receding axis

16. Oblique Drawings (con’t)
In oblique projection, the object face that is placed parallel to the frontal plane will be drawn true size and shape
Thus, the first rule in creating an oblique drawing is to place complex features (i.e., arcs, holes, or irregular surfaces) parallel to the frontal plane

17. Oblique Drawings (con’t)
In oblique drawings, dimensions lie in the plane of the surface to which they apply, and unidirectional text placement is used
Dimension text may need to be changed because only the cavalier oblique projection gives true depth.

18. Oblique Drawings (con’t)
Creating an Oblique sketch:
Step 1: Block in the front face of the object. Estimate distances to create a proportioned sketch
Step 2: Sketch depth construction lines at 30 to 45 degrees. Estimate depth along the sketched lines
Step 3: Draw a line between each depth mark to create the back edge
Step 4: Darken all visible lines including any part of a back circle that is inside a front circle

19. Perspective Drawings (2.7)
Pictorial drawings used to represent 3-D forms on 2-D media in a manner closest to how we perceive the objects with our eyes
Terms to be familiar with include horizon line (HL), ground line (GL), station point (SP), picture plane (projection plane), and vanishing point (VP)

20. Perspective Drawings (con’t)
The view of the object can be dramatically changed by moving the vanishing point along the horizon line
Points to the right of center will reveal details about the right side of the object; while points to the left of center will reveal details about the left side

21. Perspective Drawings (con’t)
The human’s eye view is the most commonly used for sketching everyday objects
The position of the view has a dramatic effect on the representation of the drawing

22. Perspective Drawings (con’t)
Perspective view drawings can be one-, two-, or three-point perspectives
Four variables to consider in perspective view drawings:
Distance of object from picture plane
Position of station point
Position of ground line
Number of vanishing points
Practice creating a one-point perspective sketch (Fig in text)

23. Perspective Drawings (con’t)

24. Next Class
Section Views
MD HW3 will be assigned.