DMT113 Engineering Drawing Chapter 3 Stretch System
Contents Theory & Multiview Planes 6 Principle Views Multiview Sketching Technique & Perspective First & Third Angle Multiview Representations
Theory & Multiview Planes theory: comprises the principles used to graphically represent 3D objects & structures on 2D media LOS (Line of Sight): Imaginary ray of light between an observer s eye and an object Plane of projection: Imaginary flat plane upon which the image created by the lines of sight is projected Parallel projection: Object to be positioned at infinity & viewed from multiple points on an imaginary line parallel to the object Perspective projection: Object to be positioned at a finite distance & viewed from a single point Ortographic projection: parallel projection technique in which the plane of projection is positioned between the observer & the object & is perpendicular to the parallel lines of sight Multiview projection: orthographic projection for which the object is behind the plane of projection & the object is oriented such that only 2 of its dimensions are shown Multiview drawings:common 3 views are shown: top view, frontal view & right side view
Theory & Multiview Planes
Theory & Multiview Planes Multiview drawing of an object
6 Principle Views 6 mutually perpendicular views that are produced by 6 mutually perpendicular planes of projection Front view Top view Right side view Left side view Rear view Bottom view
6 Principle Views
Isometric pictorial: type of parallel projection that represents all 3 dimensions in a single image
Basic steps used to create an isometric sketch of an object
Oblique pictorial: the front face is seen in its true shape & is square with the paper & only the depth axis is drawn at an angle Isometric vs oblique sketches
Visualizing a multiview drawing
Center lines: represent symmetry & paths of motion & to mark the centers of circles & axes of symmetrical parts ie cylinders & bolts Visible lines: final drafting of the technical drawing Construction lines: initial drafting of the technical drawing Hidden lines: represent features that cannot be seen in the current view Phantom lines: represent a movable feature in its different positions Cutting plane lines: used in section drawings to show the locations of cutting planes Dimension & extension lines: used to indicate the sizes of the features on a drawing Section lines: used in section views to represent surfaces of an object cut by a cutting plane
Drawing conventions for hidden lines
Creating a three view sketch
Perspective Bird s eye view Relationship: Ground line well below the horizon line Effect: Observer is much taller than the object Human s eye view Relationship: Ground line six feet below the horizon line Effect: Observer is somewhat taller than the object Ground s eye view Relationship: Ground line at the same level as the horizon line Effect: Observer is the same height as the object Worm s eye view Relationship: Ground line well above the horizon line Effect: Observer is much shorter than the object
One, two & three-point perspective sketches of the same object
Multiview Representations Multiview drawings of solid primitive shapes
First & Third Angle s
First & Third Angle s Pictorial comparison between first & third angle projection techniques
Multiview Representations Fillet: a rounded interior corner, normally found on cast, forged or plastic parts Round: a rounded exterior corner
Multiview Representations
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