Visualization and Design Engineering Graphics Stephen W. Crown Ph.D.

Objective n How to represent a 3-D object effectively on a 2-D drawing surface (pictorials) n How to visualize a 3-D object using solid primitives

Overview n Sketching Review n Pictorials PerspectivePerspective Parallel projectionParallel projection n Other Visualization Tools Solid primitivesSolid primitives MiscellaneousMiscellaneous

Sketching (review) n Definition A rough freehand drawing used to document, communicate, and refine ideas developed primarily in the ideation phase of the design process A rough freehand drawing used to document, communicate, and refine ideas developed primarily in the ideation phase of the design process n Follows standard practices n A developed skill n Should be the first step of any CAD or mechanical drawing (including homework assignments)

Pictorial Sketches n Definition: A sketch developed for ease of visualization that shows an objects height, width, and depth in a single view n Particularly useful for non-technical audiences Assembly drawingsAssembly drawings MarketingMarketing n Helpful in the ideation phase of the design process How we picture objects in our mindHow we picture objects in our mind How we visualize spatial relationshipsHow we visualize spatial relationships

Pictorial Sketches n Parallel Projection Parallel lines are always drawn parallelParallel lines are always drawn parallel Easy to drawEasy to draw Often appears distortedOften appears distorted Two common typesTwo common types –Oblique Pictorials –Isometric Pictorials n Perspective Projection Conveys information about distance and sizeConveys information about distance and size Not as common as parallel projectionNot as common as parallel projection

Parallel Projection Pictorials n Oblique Pictorials The simplest pictorial to sketchThe simplest pictorial to sketch Surfaces which are parallel to the front face are undistorted as in a multiview drawingSurfaces 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 45 oLines which are perpendicular to the front face are drawn at an angle of 30 to 45 o

Parallel Projection Pictorials n Oblique Pictorials Cavalier ObliqueCavalier Oblique –Depth is drawn full size –Object looks distorted (depth is exaggerated) Cabinet ObliqueCabinet 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 ellipticalCircular features which are not parallel to the front plane appear elliptical

TrimetricTrimetric no equal anglesno equal angles gives the most visually pleasing viewgives the most visually pleasing view DimetricDimetric Two equal anglesTwo equal angles IsometricIsometric Three equal angles (120 o )Three equal angles (120 o ) Height drawn along vertical axisHeight drawn along vertical axis Width and depth drawn at 30 o to horizontal axisWidth and depth drawn at 30 o to horizontal axis Other orientations (reversed and long axis)Other orientations (reversed and long axis) Axonometric Pictorials

Parallel Projection Pictorials n Isometric Pictorials Most commonMost common Surfaces on all principle planes are distortedSurfaces on all principle planes are distorted –All circles appear as ellipses –Perpendicular lines are drawn at 60 or angles Height drawn along vertical axisHeight drawn along vertical axis Width and depth drawn at 30 o to horizontal axisWidth and depth drawn at 30 o to horizontal axis

Parallel Projection Pictorials n Isometric Pictorials Begin drawing by blocking in height, width and depth of entire object.Begin drawing by blocking in height, width and depth of entire object. Continue to block in smaller featuresContinue to block in smaller features Add curved surfaces lastAdd curved surfaces last –circles appear as ellipses –lines tangent to arcs locate the edge of curved surfaces Isometric grid paper is often helpfulIsometric 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 45 oRotate about the Z axis 45 o Rotate about the X axis by an angle of =sin -1 (2/3 ) ½Rotate about the X axis by an angle of  =sin -1 (2/3 ) ½ An isometric projection is a true size projectionAn isometric projection is a true size projection  length along projected axes is L*(2/3) ½ An isometric drawing is drawn full scale along axesAn isometric drawing is drawn full scale along axes  objects are increased in size by a factor of (3/2) ½

Perspective Projection Pictorials n The most difficult to draw n The most visually accurate n The use of vanishing points One pointOne point –Lines of height and width are parallel –Like a “perspective oblique” Two pointsTwo points –Only lines representing height are parallel –most common perspective view Three pointsThree points –No lines are parallel

Other Visualization Tools n Solid primitives Box (Parallelepiped)Box (Parallelepiped) CylinderCylinder ConeCone SphereSphere WedgeWedge Extrude a 2-D shapeExtrude a 2-D shape Revolve a curve about an axisRevolve a curve about an axis

Other Visualization Tools n Operations on solid primitives AddAdd –assembly –welding SubtractSubtract –drilling –milling/machining IntersectionIntersection –only regions where both part are in common are retained –helpful to produce mating parts

Other Visualization Tools n Right hand rule Your thumb, index finger, and middle finger represent the X, Y, and Z axis respectively.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 rotationPoint your thumb in the positive axis direction and your fingers wrap in the direction of positive rotation

Other Visualization Tools n Always rotate parts using full 90 degree rotations n Number vertices in different views of multiview and isometric drawing n Practice