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Chapter 3Sketching / Line Types / MultiViews
Learning Objectives• After completing this chapter, you will
– 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.
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 DrawingA multiview drawing is one that shows two or more two-dimensional views of a three-dimensional 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 HeightAll three-dimensional objects have width, height, and depth.Width is associated with an object’s side-to-side dimension.Height is the measure of an object from top-to-bottom.Depth is associated with front-to-backdistance.
Width, Depth, and Height
45°
Width, Depth, and Height
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 planeonto which a two-dimensional object view will be created.
Orthographic Projection
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 three-dimensional object is projected and created.
Projection Plane
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.
1
2
3
4
5
Orthographic Projection
Projection lines are used to project each corner outward until they reach the projection plane.
Orthographic Projection
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.
Projection Lines
The visible edgesof 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.
Orthographic Projection
Sketching a Multiview DrawingGiven the overall dimensions of the object, a pencil, and a sheet of graph paper, a sketching multiviewdrawing 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
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....
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
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