CHAPTER 14

CHAPTER 14

Pictorial Drawings and Technical Illustrations

Learning Objectives

• Draw three-dimensional objects using 3-D coordinates

• Construct objects using isometric, diametric, or trimetric methods

• Construct objects using oblique drawing methods

Learning Objectives

• Draw objects using one-, two-, or three-point perspective

• Apply a variety of shading techniques to pictorial drawings

• Given an orthographic engineering sketch of a part or assembly, draw the part in pictorial form using proper line contrasts and shading techniques

Pictorial Drawings

• Often accompany 2-D orthographic multiviews• Provide a realistic 3-D view

• Help improve visualization

• Now created using CADD or illustration programs

• ASME Y14.4M, Pictorial Drawing standard

Pictorial Drawings

• Useful for a variety of applications• Clarify basic and complicated

engineering designs• Help designers and engineers work

out spatial problems• Most often the basis for technical

illustrations

Pictorial Drawings

Uses of Pictorial Drawings

Isometric Projections and Drawings

• Equal (iso) measure (metric)• Simplest form of axonometric

projection• Single scale for all axes

Isometric and Nonisometric Planes

Regular Isometric

• Most common• View the top of the object and the

object from either side

Reverse Isometric

• View the bottom of the object

Long-Axis Isometric

• Common for long objects

Isometric Construction: Box or Coordinate Method

• Most common form of isometric construction

• Used on objects that have angular or radial features

Isometric Construction: Centerline Layout Method

• Used on objects with many circles and arcs

• Circles in isometric are isometric ellipses

Isometric Circles and Arcs

Establishing Isometric Intersections

Drawing Isometric Sections

Drawing Isometric Threads

• Equally spaced elliptical arcs• Detailed thread representation

Drawing Isometric Spheres

Dimetric Pictorial Representation

• Form of axonometric projection• Two different scales for

measurement

• Missing image – go to page 566

Trimetric Pictorial Representation

• Most involved form of axonometric projection

• Three different scales for measurement

Exploded Pictorial Drawings

• Exploded assembly• Show the relationship of parts in a

realistic manner• Commonly used in:• Parts catalogues

• Owner's manuals

• Assembly instructions

Exploded Pictorial Drawings

• Isometric drawings most common• Can include centerlines between

part and subassembly axes• Can use solid extension lines

between non-cylindrical features, parts, and subassemblies

• Can include balloons

Exploded Pictorial Drawing

Oblique Drawing

• Shows three faces of the object• Useful if one face of an object

needs to be shown flat

Cavalier Oblique

Cabinet Oblique

General Oblique

Perspective Drawings

• Most realistic pictorial illustration• Show depth and distortion

perceived by the human eye• Objects appear smaller the farther

away they are until they vanish at a point on the horizon

One-point or parallel perspective Two-point or angular perspective Three-point perspective

General Perspective Drawing Concepts

One-Point Perspective

• Plan view is oriented so the front surface of the object is parallel to the picture plane

• Elevation view is placed below and to the right or left of the plan and rests on the ground line

• Used most often when drawing interiors of rooms

Two-Point Perspective

• Two principal planes are at an angle to the picture plane

• Two vanishing points provide another dimension to the depth of the perspective

• Most popular form of perspective drawing• Exteriors of houses and small buildings

• Civil engineering projects

• Machine parts (occasionally)

Three-Point Perspective

• Time consuming to construct• Often occupy a considerable area

on the drawing sheet• Used to illustrate objects having

great vertical measurements, such as tall buildings

Drawing Circles and Curves in Perspective

• Circles in perspective typically appear as ellipses

• Any circle on surface parallel to the picture plane appears as a circle

• Construction using the coordinate method

Basic Shading Techniques