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Visualization and Design Engineering Graphics Stephen W. Crown Ph.D. Objective How to represent a 3-D object effectively on a 2-D drawing surface (pictorials) How to visualize a 3-D object using solid primitives Overview Sketching Review Pictorials • Perspective • Parallel projection Other Visualization Tools • Solid primitives • Miscellaneous Sketching (review) Definition A rough freehand drawing used to document, communicate, and refine ideas developed primarily in the ideation phase of the design process Follows standard practices A developed skill Should be the first step of any CAD or mechanical drawing (including homework assignments) Pictorial Sketches Definition: A sketch developed for ease of visualization that shows an objects height, width, and depth in a single view Particularly useful for non-technical audiences • Assembly drawings • Marketing Helpful in the ideation phase of the design process • How we picture objects in our mind • How we visualize spatial relationships Pictorial Sketches Parallel Projection • • • • Parallel lines are always drawn parallel Easy to draw Often appears distorted Two common types – Oblique Pictorials – Isometric Pictorials Perspective Projection • Conveys information about distance and size • Not as common as parallel projection Parallel Projection Pictorials Oblique Pictorials • The simplest pictorial to sketch • Surfaces which are parallel to the front face are undistorted as in a multiview drawing – Circular features should be placed in the front view if possible – Draw the front face first • Lines which are perpendicular to the front face are drawn at an angle of 30 to 45o Parallel Projection Pictorials Oblique Pictorials • Cavalier Oblique – Depth is drawn full size – Object looks distorted (depth is exaggerated) • Cabinet Oblique – Depth is drawn to 1/2 of full size – Depth appears more accurate (2/3 is best) • Circular features which are not parallel to the front plane appear elliptical Axonometric Pictorials • Trimetric • no equal angles • gives the most visually pleasing view • Dimetric • Two equal angles • Isometric • Three equal angles (120o) • Height drawn along vertical axis • Width and depth drawn at 30o to horizontal axis • Other orientations (reversed and long axis) Parallel Projection Pictorials Isometric Pictorials • Most common • Surfaces on all principle planes are distorted – All circles appear as ellipses – Perpendicular lines are drawn at 60 or 1200 angles • Height drawn along vertical axis • Width and depth drawn at 30o to horizontal axis Parallel Projection Pictorials Isometric Pictorials • Begin drawing by blocking in height, width and depth of entire object. • Continue to block in smaller features • Add curved surfaces last – circles appear as ellipses – lines tangent to arcs locate the edge of curved surfaces • Isometric grid paper is often helpful – follow direction of axis and count intersections – use tracing paper or grid paper with light lines Isometric Projection and Isometric Drawings • Rotate about the Z axis 45o • Rotate about the X axis by an angle of q=sin-1(2/3)½ • An isometric projection is a true size projection ½ length along projected axes is L*(2/3) • An isometric drawing is drawn full scale along axes objects are increased in size by a factor of (3/2)½ Perspective Projection Pictorials The most difficult to draw The most visually accurate The use of vanishing points • One point – Lines of height and width are parallel – Like a “perspective oblique” • Two points – Only lines representing height are parallel – most common perspective view • Three points – No lines are parallel Other Visualization Tools Solid primitives • • • • • • • Box (Parallelepiped) Cylinder Cone Sphere Wedge Extrude a 2-D shape Revolve a curve about an axis Other Visualization Tools Operations on solid primitives • Add – assembly – welding • Subtract – drilling – milling/machining • Intersection – only regions where both part are in common are retained – helpful to produce mating parts Other Visualization Tools Right hand rule • Your thumb, index finger, and middle finger represent the X, Y, and Z axis respectively. • Point your thumb in the positive axis direction and your fingers wrap in the direction of positive rotation Other Visualization Tools Always rotate parts using full 90 degree rotations Number vertices in different views of multiview and isometric drawing Practice