Three Dimensional Drawings

1
Three Dimensional Drawings

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

2
Objective

• To learn how to generate and manipulate 3-D
  wireframe drawings
• To learn how to generate surfaces on 3-D
  wireframe drawings

3
Overview

• 3-D Coordinates
• UCS
• Specifying Coordinates
• Controlling the View
• Viewports
• VPOINT
• Drawing Aids
• Surfaces
• Example

4
The User Coordinate System

• Specify an Origin
• UCS /Origin (specify the origin relative to the
  current coordinate system)
• Reorient the axes
• UCS / Zaxis (choose the direction of the Z axis)
• UCS / 3point (choose the origin and the positive
  X and Y direction)
• UCS / Z (specify the angle of rotation about the
  Z axis)
• Save and Restore the UCS
• UCS / Save and UCS / Restore

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Right Hand Rule

• Thumb points in the positive x direction
• Index finger points in the positive y direction
• Middle finger points in the positive z direction
• Used to define positive rotation
• Point thumb in the positive direction along the
  axis which is perpendicular to the plane of
  rotation
• The fingers point in the direction of positive
  rotation

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Specifying 3-D Coordinates

• Specify a 2-Dimensional Coordinate
• Cartesian (x,y)
• Polar (rltq)
• q is the angle in the xy plane
• If absolute coordinates are specified both z
  and f are assumed to be zero
• If relative coordinates are specified then the
  previous value of z is used, however f is
  still assumed to be zero

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Specifying 3-D Coordinates

• Specify a 3-Dimensional Coordinate
• If in doubt about coordinates specify 3-D
  coordinates
• Use relative or absolute coordinates
• Cartesian (x,y,z)
• Spherical (rltqltf)
• q is the angle in the xy plane
• f is the angle from the xy plane
• Can not specify cylindrical coordinates (z,r,q)

8
Understanding the World Coordinates in Different
Views

• Top View
• XY plane
• Front View
• XZ plane
• Right View
• YZ plane

9
Using Viewports

• Create multiple viewports in paper space using
  MVIEW
• If using A-PROTO first delete the existing
  viewport
• Creating 4 viewports is convenient for 3-D
  drawings
• Each viewport is a controllable view of one model
  space
• Only one viewport is active at a time

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Using Four Viewports

• View the object using the three standard views
  (top, front, and side)

• View the object as a pictorial in a fourth view
• Center each view and use the same scale to give
  the appearance of a multiview drawing

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Controlling the View

• Use VPOINT to set the view for each viewport
• The point specified is the location of the camera
  and it is pointed toward the origin
• EX 0,0,1 is a view looking down the z-axis
  toward the origin. This is also called the PLAN
  view.
• Use VIEW to save or restore a view
• Call the four views top, front, side, and iso
• You may also save other helpful views

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Controlling the View

• The settings shown will give the standard views
  for a multiview drawing
• A pictorial view will be shown in the upper right
  hand viewport

• You must make a viewport active to change the
  viewpoint
• Changing the UCS affects all viewports

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Using Different Viewports

• .xy
• .xz
• .yz
• Use object snap

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Application Auxiliary Views

• The true shape of an object is easy to find when
  drawn as a 3-D object
• Use UCS / 3point and PLAN to find the true shape
  view
• Use UCS / Zaxis and PLAN to find the edge view

15
Drawing Aids For 3-D Drawings

• Object snap
• several different points may be defined if you
  are not careful in the selection of entities
• choose the best view
• use filters and multiple views (.xy, .xz, and
  .yz)
• Use apparent intersection when appropriate
• Trim
• always use UCS / View before using trim
• Trim boundaries extend infinitely along the z axis

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Adding Surfaces to 3-D Drawings

• Wireframe drawings do not distinguish hidden
  features
• Add surfaces to a wire frame drawing using 3DFACE
• Create a separate layer called face
• Define points on face in a clockwise or
  counter-clockwise manner
• Faces may be continued using the last two
  vertices
• Use I when appropriate

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Invisible Lines with 3DFACE

• Type I before selecting the first vertex of the
  invisible line
• Example
• 3dface
• first vertex B
• second vertex C
• third vertex I
• third vertex D
• forth vertex A
• third vertex F
• forth vertex E

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Curved Surfaces

• Curved surface and surfaces with curved
  boundaries are much easier to draw using solid
  modeling
• 3-D objects
• several standard surface models (3dface) may be
  generated in CAD using a set of predefined shapes
  including some curved surfaces
• Revolved surfaces (REVSURF)
• creates a surface by revolving a path curve about
  a defined axis
• Generates a faceted surface controlled by
  SURFTAB1 and SURFTAB2

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Example REVSURF

• Draw the axis of revolution
• Draw the path curve
• Only one path curve can be revolved at a time
• Use PEDIT to join multiple lines into a single
  path curve

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Hide and Shade

• HIDE removes hidden lines giving a realistic 3-D
  view
• SHADE also removes hidden lines but colors in
  surfaces according to their entity color
• REGEN resets the drawing to show the hidden lines

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Example

• Begin with a wireframe drawing using the x,y,z
  coordinates of each vertex
• Use the XY plane as the surface which the object
  rests on
• Use COPY to repeat vertices at different Z
  elevations

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Example

• VPOINT
• 1,-3,2
• LINE
• From point 0,0,0
• To point 3,0,0
• To point _at_0,1,0
• To point _at_3lt180lt0
• To point close

• COPY
• Select objects all
• Base point 0,0,0
• Second point 0,0,.25

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Example

• DDOSNAP
• Endpoint
• Line
• (Connect end points)