Pictorials and Multiview Drawings using CAD

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Pictorials and Multiview Drawings using CAD

• Engineering Graphics
• Stephen W. Crown Ph.D.

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Objective

• How to represent a 3-D object effectively on a
  2-D drawing surface with a single view
  (pictorials)
• How to generate pictorials and multiview drawings
  using CAD

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Overview

• Pictorial Drawings
• Review and some added details
• Pictorials with CAD
• Isometric, Perspective, Cabinet Oblique

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Pictorials (Review)

• 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
• Pictorials are generally not dimensioned
• Surfaces are often shaded and hidden lines not
  shown
• Helpful in the ideation phase of design
• May be easily drawn with CAD programs

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Pictorials (review)

• Parallel Projection
• Oblique Pictorials
• Parallel projectors are not perpendicular to the
  projection plane
• Axonometric Pictorials
• Projection lines are perpendicular to the
  projection plane as in a multiview drawing
• Ex. Isometric
• Perspective Projection
• Conveys information about distance and size
• Not as common as parallel projection

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Pictorials (review)

• Oblique Pictorials
• The simplest pictorial to sketch
• Surfaces which are parallel to the front face are
  undistorted as in a multiview drawing
• Place circular features in the front view if
  possible
• Draw the front face first
• Orient the object such that long features appear
  in the frontal plane
• Lines which are perpendicular to the front face
  are drawn at an angle of 30 to 45o (other angles
  may be used to better illustrate features)
• Cavalier Oblique (Full size depth)
• Cabinet Oblique (1/2 size depth)

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Pictorials (review)

• Oblique Pictorials
• Locate endpoints of lines on oblique surfaces in
  the principle planes and then connect endpoints
• Hidden and center lines are generally not shown
  unless the part is dimensioned
• occasionally oblique drawings are dimensioned
• refer to ANSI Y14.4M if dimensioned
• If circular or irregular features must appear in
  planes other than the frontal plane use
  orthographic projection (isometric pictorial)
• Can not be easily generated from solid models
  using CAD

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Oblique Drawings using CAD

• Box in the overall height and width of the object
  in the frontal plane (RECTANG)
• Copy the box at a distance equal to 1/2 the depth
  (cabinet oblique) and at an angle of 45o (_at_1lt45)
• Connect the endpoints of the boxes (use DDOSNAP
  ENDPOINT)
• Rotation of UCS may also be helpful if used with
  ORTHO

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Oblique Drawings using CAD

• Circular features
• Draw circular features in frontal plane
• Copy features to different depth positions using
  the same procedure outlined for rectangular
  features (_at_Dlt45)
• Draw visible boundaries using tangent lines

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Pictorials (review)

• 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)
• All circles appear as ellipses

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Isometric Projection and Isometric Drawings

• Rotate about the Z axis 45o
• Rotate about the X axis by an angle of
  qsin-1(1//3)
• An isometric projection is a true size projection
• 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)

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Pictorials (review)

• 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
• Isometric grid paper
• follow direction of axis and count intersections
• use scaled grid paper for isometric projection
• Hidden and center lines are generally not shown
• occasionally isometric drawings are dimensioned
• refer to ANSI Y14.4M-1989 if dimensioned

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Pictorials (review)

• Isometric Pictorials
• Nonisometric lines
• Locate endpoints in principle planes
• Oblique surfaces
• Locate endpoints of surface boundary lines
• Box in curved surfaces
• Irregular surfaces
• Locate several points along the curve
• Connect points with a smooth curve

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Isometric Drawings Using CAD

• Use the isometric snap/grid (DDRMODES)
• Circles are drawn using the ELLIPSE command and
  ISOCIRCLE
• Choose the orientation of ellipses by selecting
  different faces

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Isometric Drawings Using CAD

• Box in the overall height, width, and depth of
  the object using the isogrid
• do not make the grid too small as it is difficult
  to move the cursor
• set the coordinates to display relative distances
  (COORDS lt2gt)
• The isogrid may be used for isometrics and then
  turned off for multiview drawings
• Isometric drawings are easily generated using
  solid models and the correct viewpoint
• (VPOINT 1,1,1)

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Pictorials (review)

• Perspective Projection Pictorials
• 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

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Pictorials (review)

• Perspective Projection Pictorials
• Selection of vanishing points
• number of points (1, 2, or 3)
• location relative to center of object dictates
  orientation
• locate two vanishing points on the horizon
• distance from object dictates relative size
• Projection plane is called picture plane
• parallel lines which are not parallel to the
  picture plane converge
• Box in object with rays from vanishing points

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Perspective Drawings using CAD

• Choose vanishing points and draw one ray from
  each
• other rays are easily constructed using DDOSNAP
  ENDPOINT
• trim rays using FILLET with R0 to keep drawing
  from getting too busy (especially for 3 V-points)
• keep one reference ray from each vanishing point
• Simple to make a rough sketch but difficult to
  make dimensionally accurate (especially if there
  are curved features)
• Can be easily generated from solid models or 3-D
  wire frame drawings

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Perspective Drawings using CAD

• Simple to make a rough sketch but difficult to
  make dimensionally accurate (especially if there
  are curved features)
• Can be easily generated from solid models or 3-D
  wire frame drawings using dynamic view (DVIEW)
• distance
• camera
• target

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Multiview drawings in CAD

• Construction lines using ORTHO
• Miter line for adjacent view