Understanding Solid Objects

Understanding Solid Objects

• Envisioning objects in three dimensions is important for those in science, design, engineering, and technical fields.
• Spatial visualization can be improved through studying technical drawing.
• Sketching is a valuable tool for communicating ideas quickly and accurately, and a picture during development can be invaluable.
• Use sketching to plan drawings and record notes for complex objects, and it will allow for the final CAD drawing to be completed sooner and with fewer errors.
• Good sketching facilitates speed, ease, and legibility

Understanding Solid Objects

• Sketches and drawings communicate or record ideas about 3D object shapes
• Vocabulary is important for understanding and discussing 3D shapes prior to sketching
• Three-dimensional figures are solids, bound by surfaces
• Types of surfaces include:
• Planar
• Single Curved
• Double Curved
• Warped
• Complex solids are a combination of basic surface types

Types of Solids

• Solids bounded by plane surfaces are polyhedra
• Planar surfaces are referred to as faces
• Polygons are planar areas enclosed by straight lines

Regular Polyhedra

• Regular polyhedra are solids with equal regular polygon faces
• Five regular polyhedra:
• Tetrahedron
• Hexahedron
• Octahedron
• Dodecahedron
• Icosahedron

Prisms

• Prisms have two parallel, equal polygon bases and three or more parallelogram faces
• Triangular prisms have triangular bases
• Rectangular prisms have rectangular bases
• A prism with parallelogram bases is a parallelepiped

Right and Oblique Prisms

• Right prisms have faces and lateral edges perpendicular to the bases
• Oblique prisms have faces and lateral edges angled to the bases
• Prisms truncated when one end is cut to be non-parallel to the bases

Pyramids

• Pyramids have a polygon base and triangular lateral faces intersecting at a vertex
• The axis is the line from the base center to the vertex
• Right vs oblique pyramids depend on whether the axis is perpendicular to the base
• Triangular and square pyramids have triangular and square bases, respectively
• Truncated pyramids, or frustums, occur when a portion near the vertex is cut off

Cylinders

• Cylinders have a single-curved exterior surface
• Enclose a volume by moving a straight line in a circle
• Element refers to each position of the imaginary straight line around the axis

Cones

• Cones have a single-curved exterior surface
• Formed by moving one end of a straight line around a circle and fixing the other end at a vertex
• Element refers to any position of the imaginary straight line

Spheres

• Spheres have a double-curved exterior surface
• They are formed by revolving a circle about one of its diameters
• Poles are the top and bottom points that do not move during spinning
• Axis of the sphere is the line between its poles

Tori

• Tori are doughnut-shaped with a double-curved boundary surface
• They are formed by revolving a circle (or curve) around an axis positioned away from the curve

Ellipsoids

• Oblate/prolate ellipsoids are egg-shaped
• They are formed by revolving an ellipse about its minor/major axis respectively

Ellipsoids

• 3D modeling allows solid, wireframe, and mesh models
• Benefits of 3D Modeling:
• View from any vantage point
• Generate reliable standard and auxiliary 2D views automatically
• Create sections and 2D drawings
• Remove hidden lines and do realistic shading
• Check interferences
• Add lighting
• Create realistic renderings
• Navigate the model
• Use the model to create an animation
• Perform engineering analysis
• Extract manufacturing data

Solid Modeling

• Utilizing solids and surfaces as building blocks when creating solid models
• A solid object represents the entire volume
• Solids are the most complete and least ambiguous of the 3D model types
• Complex shapes are easier to construct and edit than wireframes and meshes
• User coordinate system can be relocated and rotated for convenient coordinate entry, grid display, grid snap, and Ortho mode

World and User Coordinate Systems

• There are two coordinate systems:
• World Coordinate System (WCS) which is fixed
• User Coordinate System (UCS) which is movable
• By default these systems are coincident in a new drawing
• WCS X axis is horizontal and the Y axis is vertical in 2D views
• WCS origin is where the X and Y axis intersect at (0,0)
• All objects in a drawing file are defined by their WCS coordinates
• It is usually more convenient to create and edit objects based on the movable UCS

Specify Workplanes in 3D (UCS)

• User coordinate system control is essential for effective 3D modeling
• Understanding the User Coordinate System in 3D
• When working in 3D, the user coordinate system is useful for:
• Entering Coordinates
• Creating 3D objects on 2D workplanes
• Rotating objects in 3D
• When creating or modifying objects in 3D:
• Move and reorient the UCS to make work simpler
• The XY plane of the UCS is the "workplane"
• Important operations on objects in a 3D environment that depend on the location and orientation of the UCS:
• Establish the workplane for modification and creation.
• Establish the workplane for the grid and grid snap.
• Establish a new UCS Z axis to allow for object rotation.
• Determine directions and horizontal/vertical for Ortho mode, polar tracking, and object snap tracking.
• Define a 3D view into the workplane with the PLAN command.

Controlling The User Coordinate System in 3D

• Several methods are available for manipulating the user coordinate system in 3D.
• User coordinate system orientations can be saved and restored
• Change the UCS to change
• 0,0,0 origin point
• the location and rotation of the XY plane
• the orientation of the XY plane or Z axis.
• UCS locations can be defined, saved, and recalled as needed

Overview of Creating 3D Solids and Surfaces

• Basic 3D shapes (solid primitives):
• boxes
• cones
• cylinders
• spheres
• wedges
• pyramids
• tori (donuts).
• These shapes can later be combined to create more complex solids by:
• joining
• subtracting
• finding their intersecting (overlapping) volume.
• 3D objects can also be made from existing objects through:
• Extruding
• Sweeping
• Revolving
• Lofting
• Slicing
• Converting planar objects with thickness into solids and surfaces Solids and surfaces are displayed in the visual style applied to the viewport. Solids have mass properties: volume момента of inertia, center of gravity:
• Solid object data is exportable to NC milling/FEM analysis.
• Exploding a solid breaks it down to regions, bodies, surfaces, and wireframe objects.

The ISOLINES System Variable

• Manages tessellation lines that are used to show curved parts of the wireframe

The FACETRES System Variable

• Adjusts the smoothness of shaded and hidden-line objects
• 3D solids save their original forms by default
• This history allows the original forms that make up solids to remain visible

Creating 3D Solid Primitives - Solid Box

• Use the Cube option of the BOX command to create a box with sides of equal length
• To create a solid box:
• Click Draw menu, Modeling, Box
• Specify the first corner of the base
• Specify the opposite corner of the base
• Specify the height

Creating 3D Solid Primitives - Solid Wedge

• Click Draw menu, Modeling, Wedge for a solid wedge
• Specify the first corner of the base
• Specify the opposite corner of the base
• Specify the height

Creating 3D Solid Primitives - Solid Cone

• Click Draw menu, Modeling, Cone for a solid cone
• Specify the center point of the base
• Specify the radius or diameter of the base
• Specify the height of the cone

Creating 3D Solid Primitives - Solid Cylinder

• Click Draw menu, Modeling, Cylinder for a solid cylinder
• Specify the center point of the base
• Specify the radius or diameter of the base
• Specify the height of the cylinder

Creating 3D Solid Primitives - Solid Sphere

• Click Draw menu, Modeling, Sphere for a solid sphere
• Specify the center of the sphere
• Specify the radius or diameter of the sphere

Creating 3D Solid Primitives - Solid Pyramid

• Click Draw menu, Modeling, Pyramid for a solid pyramid
• Specify the center point of the base
• Specify the radius or diameter of the base
• Specify the height of the pyramid

Creating 3D Solid Primitives - Solid Torus

• Click Draw menu, Modeling, Torus for a solid torus
• Specify the center of the torus
• Specify the radius or diameter of the torus
• Specify the radius or diameter of the tube

Drawing A Polysolid

• Click Draw menu, Modeling, Polysolid to draw it
• Specify the starting point
• Specify the next point
• Repeat step 3 to finish the shape
• Press Enter to finish

Extruding Objects

• Extruding a closed object results in a solid
• Extruding an open object creates a surface
• Objects that can be extruded:
• Lines
• Arcs
• Elliptical arcs
• 2D polylines
• 2D splines
• Circles
• Ellipses
• 3D faces
• 2D solids
• Traces
• Regions
• Planar surfaces
• Planar faces on solids cannot be extruded
• Cannot extrude polylines with crossing or self-intersecting segments
• Cannot extrude blocked objects
• Polyline width is ignored and the polyline is extruded from the center of its path
• Thickness of a selected object is ignored

Extrusion Options

• You can specify the following options when extruding objects:
• Path
• Taper angle
• Direction

Specifying a Path for an Extruded Solid

• Use the Path option to use an object as the path for extrusion
• The profile of the selected object is extruded along the path to create a solid or surface
• It's recommended for the path to lie on or within the boundary of the extruded object for best results
• Usage differs from sweeping
• In extrusion the path is moved to the profile if it isn't already there
• Then the profile is swept along the path
• Using a path with the SWEEP command provides greater control, however

Path Objects

• The following objects can be paths:
• Lines
• Circles
• Arcs
• Ellipses
• Elliptical arcs
• 2D polylines
• 3D polylines
• 2D splines
• 3D splines
• Edges of solids
• Edges of surfaces
• Helixes

Specifying a Taper Angle for an Extruded Solid

• Tapering is useful for parts that need sides at an angle
• Tapered angles should not be too large
• The profile can taper to a point before reaching the specified height if the angle is too big

Specifying a Direction for an Extruded Solid

• Direction option allows setting extrusion length/direction by setting two points

To Extrude an Object

• Click Draw menu, Modeling, Extrude
• Select the object(s) to extrude, press Enter
• Specify the height
• The original object(s) may be deleted or retained depending on the DELOBJ system variable setting

Creating a Solid or Surface by Sweeping

• With the SWEEP command, create a new solid or surface by sweeping an open or closed planar curve (profile) along an open or closed 2D or 3D path
• Sweeping a closed curve along a path creates a solid; sweeping an open curve creates a surface
• Sweeping is different from extruding; when sweeping, the profile moves along a path aligned normally (perpendicular) to the path

Sweeping Tips & Options

• For sweeping a profile along a helix, move/rotate into place, turn off Alignment in SWEEP command
• Ensure that results do not intersect if you get a modeling error
• When sweeping objects, they can be twisted or scaled
• Use the Properties palette to control the following:
• Profile Rotation
• Scale Along Path
• Twist Along Path
• Bank (natural rotation)

Sweeping Restrictions

• The Properties palette will not allow changes if the Alignment option was turned off, or if the change creates a modeling error like a self-intersecting solid
• There is no warning message
• If more than one object is swept at a time, they must all lie on the same plane

Steps to Sweep

• Click Draw menu, Modeling, Sweep
• Select objects to sweep
• Press Enter
• Select the sweep path

Revolving

• The result is solid when a closed object is revolved, and a surface when an open object is revolved
• More than one object can be revolved at a time
• You can select any of the following as the axis to revolve objects around:
• Axis defined by two points you specify
• X-axis
• Y-axis
• Z-axis
• Axis defined by an object (object option)

PEDIT Command

• Use the PEDIT Join option before REVOLVE to create a solid using a profile made with lines or arcs
• Otherwise, revolving them will make a surface
• The REVOLVE command cannot be used on objects within a block or polylines with crossing/intersecting segments.

Revolving Objects

• Click Draw menu, Modeling, Revolve
• Select the object(s) to revolve
• Specify the start and endpoints of the axis of revolution, placing the object on one side
• The positive axis direction should go from start to endpoint
• Specify the angle of revolution

Converting Objects

• Converting objects with thickness to extruded solids:
• Click Modify menu > 3D Operations > Convert to Solid
• Select the objects with thickness:
• Uniform-width polylines
• Closed, 0-width polylines
• Circles
• Press ENTER
• Converting one or more objects to surfaces needs the following:
• Click Modify menu -> 3D Operations -> Convert to Surface.
• Select the objects
• Press ENTER
• Convert to Surface in 3D Make Panel

Planar Surfaces

• To create a planar surface from an existing object:
• Click Draw menu -> Modeling -> Planar Surface
• Type o then Press ENTER
• Select the object then Press ENTER
• To create a planar surface by specifying corners:
• Click Draw menu -> Modeling -> Planar Surface
• Specify the first corner, then the second corner
• Make panel, Planar Surface

Solidifying Surfaces

• Click Modify menu -> 3D Operations -> Thicken to convert one or more surfaces to solids
• Select the surfaces
• Press ENTER
• Specify a thickness for the solid
• Press ENTER
• Make panel, Thicken Surface

Creating Composite Solids

• UNION combines the total volume of two or more solids or two or more regions into one composite object
• Click Modify menu, Solid Editing, Union
• Select the objects to combine
• Press ENTER

Subtracting Solids

• With SUBTRACT, you remove the common area of one set of solids from another
• For example, this can add holes to part by subtracting cylinders
• Click Modify menu, Solid Editing, Subtract
• Select the objects to subtract from
• Press ENTER
• Select the objects to subtract
• Press ENTER

Intersecting Solids

• INTERSECT creates a composite solid from the common volume of multiple overlapping solids
• The non-overlapping portions are removed
• To create a solid from the intersection of two or more other solids:
• Click Modify menu > Solid Editing > Intersect
• Select the objects to intersect
• Press ENTER

Slicing

• The following objects can be used with Slice as the cutting plane
• Surfaces
• Circles
• Ellipses
• Circular or elliptical arcs
• 2D splines
• 2D polyline segments
• Slicing solids requires the following:
• Click Modify menu - 3D Operations - Slice
• Select the objects
• Press ENTER
• Define the cut plan by clicking two points
• Specify which side to retain, or retain both
• Using Planar Objects and Surfaces when slicing solids requires the following:
• Click Draw menu - 3D Operations - Slice
• Select objects
  • Press ENTER
• On the command line enter o (object) or s (surface) -Press ENTER
• Select the circle, ellipse, arc, 2D spline, or 2D polylines to use as the cutting object
• Specify which side to retain, or enter b to retain both sides