Ch.5 Pictorial Drawings

Isometric drawings (6.1 & 6.2) Theory of isometric projection (fig5.9), Position of isometric axes (fig6.10 to 12), Standards for hidden lines, center lines, and dimensioning (fig6.13 to 15), isometric drawing construction (fig6.17 to 42)

Oblique drawings (6.3) Oblique projection theory & classification (fig6.46 to 50), object orientation rules (fig5.51 to 55), dimensioning (fig6.65), oblique drawing construction (fig6.56 to 64)

Perspective drawings (6.4-6.7) Perspective vs. orthogonal (fig6.69), vanishing point position and ground line position (fig6.17 & 6.73), classification of perspective drawing (fig6.74), perspective drawing variables selection (6.7).

Objective: Learn how to construct three types of pictorial drawings – Isometric, oblique, and perspective

Comparison of Isometric, oblique, and perspective drawings

Examples

Perspective

Isometric drawings Depending on where you place isometric

axes, you get different views (Use the most effective position to meet your need)

About isometric and non-isometric lines and planes

True-length distances can only be measured along isometric lines, that is, lines run parallel to any of the isometric axes.

Dealing with hidden lines and center lines in isometric drawingsHidden lines are omitted unless they are absolutely necessary. Center lines are drawn only for showing symmetry or for dimensioning. Normally center lines are not shown.

Dimensioning in isometric drawings

Constructing an isometric drawing using the Boxing-In method

Box in from the outmost shape to inside details.

What if you have non-isometric lines?

Remember that true-length distances can only be measured along isometric lines, that is, lines run parallel to any of the isometric axes.

What if you have curves? use the Off-set Coordinate method works.

Another example of the Offset Coordinate method

Oblique Drawings

Oblique projection is a form of parallel projection in which the projectors are parallel to each other but are not perpendicular to the projection plane.

Common oblique angles

Oblique drawing types: cavalier, cabinet, and general oblique

Some hints to select the most important object face

In oblique projection, first, the object face that is placed parallel to the frontal plane will be drawn true size and shape.

Dimensioning in oblique drawings 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.

Constructing an oblique drawing using the Box-In method

Constructing an oblique drawing using the Offset Coordinate method

When we have arcs and curves, this method is always the easiest method.

Perspective drawings

Terms that you want to be familiar with: horizon line, ground line, station point, picture plane (projection plane), and vanishing point.

Position of the vanishing point and ground line and resulting perspective projections

One-, two-, and three-point perspective drawings

4 variables in perspective drawings:

Distance of object from picture plane

Position of station point

Position of ground line

Number of vanishing points