Chapter 3
Sketching / Line Types / MultiViews
Learning Objectives
• After completing this chapter, you will
–
–
–
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Sketch several types of geometry
Sketch multiviews of an object
Sketch pictorials of an object
Understand the relationship between CADD and
sketching
COMMON DRAFTING LINE TYPES
• Object lines: Bold continuous lines.
•
• Construction lines: Very light thin
continuous lines.
• Hidden lines _ _ _ _ _ _ _ _ _ _ Dashed lines
used to represent hidden features.
• Center lines _____ _ _____ Used to locate the
center of arcs, circles, etc. (thin).
• Phantom lines _____ _ _ ______ Used to
illustrate features which do not truly
exist, for example section cuts, the
extents of travel for machine parts, etc.
Line Types
Dimensioning
Part I
Sketching
Definition
• Freehand drawing
– Without instruments
– Necessary items
• Pencil
• Paper
• Eraser
• Fast visual communication
Uses of Sketches
•
•
•
•
•
Convey technical information
Organize thoughts
Minimize errors on final drawing
Record stages of progress of design
Substitute for production drawings
– Unique items
• Describe product artistically
Tools for Sketching
• Pencil
– #2 pencil
– Automatic 0.7 or 0.9 mm pencil
• F or HB lead
• Paper
– Almost any kind works, including napkins!
– Graph paper is good
• Eraser
Sketching Straight Lines
Sketching Circular Lines
Sketching Circular Lines
Sketching Circular Lines
• Other alternatives
– Centerline method
– Hand-compass method
– Trammel method
Sketching Arcs
Proportions
• All object lines are related to one another
– Entity must be kept in proportion
• Sketch should be large enough to be clear
– However…
• Proportions of features are more important
• The first line determines the scale
– “The Measurement Line”
Proportions
• The Block Technique
– Start with a rectangle
• Determines size of object
– Sketch object inside rectangle
• Use measurement line technique
Multiview Drawing
A multiview drawing is one that shows two
or more two-dimensional views of a threedimensional object.
Multiview drawings provide the shape
description of an object. When combined
with dimensions, multiview drawings serve
as the main form of communication
between designers and manufacturers.
Multiview Drawing
Width, Depth, and Height
All three-dimensional objects have width,
height, and depth.
Width is associated with an object’s side-toside dimension.
Height is the measure of an object from topto-bottom.
Depth is associated with front-to-back
distance.
Width, Depth, and Height
Width, Depth, and Height
45°
Orthographic Projection
Orthographic projection is a technique that
is used to create multiview drawings.
Orthographic projection is any projection of
the features of an object onto an imaginary
plane of projection. The projection of the
features of the object is made by lines of
sight that are perpendicular to the plane of
projection.
Orthographic Projection
The best way to
understand
orthographic
projection is to
imagine an object
contained inside
a glass box.
Orthographic Projection
There is a total of
six glass walls
surrounding the
object. Each wall
represents a
projection plane
onto which a twodimensional object
view will be created.
Projection Plane
A projection plane, also referred to as a
plane of projection or picture plane, is an
imaginary surface that exists between the
viewer and the object.
The projection plane is the surface onto
which a two-dimensional view of a threedimensional object is projected and
created.
Orthographic Projection
Start by focusing
only on the front
projection plane.
A person standing in
front of the object
would see only the
five corners
identified in black.
2
3
1
4
5
Orthographic Projection
Projection lines are
used to project each
corner outward until
they reach the
projection plane.
Projection Lines
A projection line is an imaginary line that is
used to locate or project the corners,
edges, and features of a three-dimensional
object onto an imaginary two-dimensional
surface.
Orthographic Projection
The visible edges
of the object are
then identified on
the projection
plane by
connecting the
projected corners
with object lines.
Orthographic Projection
The orthographic
projection process
is then repeated
on the other
projection planes.
Sketching a Multiview Drawing
Given the overall
dimensions of the
object, a pencil, and a
sheet of graph paper,
a sketching multiview
drawing can be easily
done using points,
construction lines, and
object lines.
Definition
• Also known as orthographic projection
• 2D views of an object
– Established by a line of sight
• Conventional views
– Top
– Front
– Right side
Multiview Sketch
Sketching a Multiview Drawing
Step #1: Calculate the amount of space that
the views will take up.
Part II
Multiview Sketches
Definition
• Also known as orthographic projection
• 2D views of an object
– Established by a line of sight
• Conventional views
– Top
– Front
– Right side
Multiview Sketch
Miter Line
• Miter lines are a convenient method for
laying out a third view when drawing the
primary planes or views on paper.
• Any horizontal movement of the miter line to
the left or right controls the distance
between the views to allow space for
dimensioning.
Miter Line
Part III
Pictorial Sketches
Pictorials
• Axonometric
– Isometric
– Dimetric
– Trimetric
• Obliques
• Perspective
Axonometric
• "Axonometric" means "to measure along
axes.
• Within orthographic projection, axonometric
projection shows an image of an object as
viewed from a skew direction in order to
reveal more than one side in the same
picture,
– unlike other orthographic projections which
show multiple views of the same object along
different axes.
Dimetric
• A dimetric projection is an axonometric
projection where two of an objects axes
make equal angles with the plane of
projection and the third angle is larger or
smaller than the other two.
• Axonometric projection is type of
graphical projection technique,
– used to create a pictural drawing of an object
by rotating the object on an axis relative to a
projection, or picture plane....
Dimetric
Oblique projection
• Oblique projection is a type of parallel
projection:
• it projects an image by intersecting parallel
rays (projectors) from the three-dimensional
source object with the drawing surface
(projection plan).
Trimetric Projection
• The direction of viewing is such that all of
the three axes of space appear unequally
foreshortened.
• The scale along each of the three axes and
the angles among them are determined
separately as dictated by the angle of
viewing.
Perspective
• To see a drawing, is an approximate
representation, on a flat surface (such as
paper), of an image as it is perceived by the
eye.
Perspective
• The two most characteristic features of
perspective are that objects are drawn:
– Smaller as their distance from the observer
increases
– Foreshortened: the size of an object's
dimensions along the line of sight are relatively
shorter than dimensions across the line of sight
Isometrics
• Provide 3D representation
• Horizontal lines
– Drawn at 30-degree angles
• Vertical lines
– Drawn vertical
Isometric Axis
Isometric Sketch
Isometric Sketch
Isometric Sketch
Isometric Sketch
Isometric Sketch
Isometric Sketch
Isometric Sketch
Isometric Circles
• Circles and arcs
– Appear as ellipses
• Need to know relationship between circle
and plane of the isometric cube
– Left plane
– Horizontal plane
– Right plane
Isometric Circles
Part IV
CADD Sketching
Sketching and Parametric Models
• In parametric modeling applications
– Profiles of geometry are “rough sketched”
• In proportion to actual object
• Not a lot bigger or smaller than final product
– Two steps
• Use of line, arc, and/or circle command
• Dimensions and constraints modified
– 3D model developed after sketching
Summary
• Sketches are completed without instruments
except pencil, paper, and eraser
• Sketches are helpful for
– Conveying technical information
– Producing preliminary drawings before transferring to
CAD
– Marketing and documentation
• CADD sketches are used to define geometry of
3D parametric models