Docstoc

Objective

Document Sample
Objective Powered By Docstoc
					AutoCAD                                       Regions and Solids                           CAD Fundamentals II
Assignment 4                                                                                   Architecture 521

Objective
To learn to use the Solid Modeling commands to create, manipulate, and measure Solids.

I did not write this:
Although 3D models can be more difficult and time-consuming to create than 3D views of 2D objects, 3D
modeling has several advantages. You can

● View the model from any vantage point
● Generate reliable standard and auxiliary 2D views automatically
● Create 2D profiles ( SOLPROF)
● Remove hidden lines and do realistic shading
● Check interference
● Export the model to create an animation
● Do engineering analysis
● Extract manufacturing data

AutoCAD supports three types of 3D modeling: wireframe, surface, and solid. Each type has its own creation
and editing techniques.

A wireframe model is a skeletal description of a 3D object. There are no surfaces in a wireframe model; it
consists only of points, lines, and curves that describe the edges of the object. With AutoCAD you can create
wireframe models by positioning 2D (planar) objects anywhere in 3D space. AutoCAD also provides some 3D
wireframe objects, such as 3D polylines (that can only have a CONTINUOUS linetype) and splines. Because
each object that makes up a wireframe model must be independently drawn and positioned, this type of
modeling can be the most time-consuming.

Surface modeling is more sophisticated than wireframe modeling in that it defines not only the edges of a 3D
object, but also its surfaces. The AutoCAD surface modeler defines faceted surfaces using a polygonal mesh.
Because the faces of the mesh are planar, the mesh can only approximate curved surfaces. With Mechanical
Desktop®, you can create true curved surfaces. To differentiate these two types of surfaces, AutoCAD calls
faceted surfaces, meshes.

Solid modeling is the easiest type of 3D modeling to use. With the AutoCAD solid modeler, you can make 3D
objects by creating basic 3D shapes: boxes, cones, cylinders, spheres, wedges, and tori (donuts). You can
then combine these shapes to create more complex solids by joining or subtracting them or finding their
intersecting (overlapping) volume. You can also create solids by sweeping a 2D object along a path or
revolving it about an axis. With Mechanical Desktop, you can also define solids parametrically and maintain
associativity between 3D models and the 2D views that you generate from them.

Warning! Because each modeling type uses a different method for constructing 3D models and editing
methods vary in their effect on the different model types, it is recommended that you not mix modeling
methods. Limited conversion between model types is available from solids to surfaces and from surfaces to
wireframes; however, you cannot convert from wireframes to surfaces or from surfaces to solids.




Exercise:
This is an assignment that involves exercising the AutoCAD built-in facilities for solid and region modeling.




                                                        1
                                                        2


In this assignment, you will work through the AutoCAD commands for creating and manipulating solids. In
addition to true 3D solids, AutoCAD also provides the 2D equivalent of 3D solids, called “regions”. Many of the
operations for manipulating regions and solids are similar, since regions are just a two-dimensional analogue
of solids. The REGION command provides an interface to create regions. On the other hand, and rather
confusingly, the SOLID (which makes pathetic 2D quadrilaterals) command does not create real 3D solids, as
you might imagine. Instead, there are several commands that are used to create solids (BOX, CONE,
WEDGE, CYLINDER, SPHERE and TORUS), and several more that are used to manipulate them (UNION,
INTERSECT, SUBTRACT, INTERFERENCE, SLICE and SECTION). In addition, there are a few commands
that allow you to make solids by extruding or revolving 2D elements (EXTRUDE, REVOLVE). Many of these
commands can be applied to create and modify both solids as well as regions. Also, many more basic
AutoCAD commands like FILLET and CHAMFER can be applied to solids.

Polygon

  1.      Sketch a polygon (closed POLYLINE).

  2.      Use the FILLET command to round some of the corners.

  3.      Add a circle inside the polygon.




  4.      Go to step 5.

Prism

  5.      Make REGIONs of the outer polygon and circle.

          Closed polylines, lines, and curves are valid selections to the REGION command. Curves
          include circular arcs, circles, elliptical arcs, ellipses, and splines. AutoCAD converts
          closed 2D and planar 3D polylines in the selection set to separate regions and then
          converts polylines, lines and curves that form closed planar loops. If more than two
          curves share an endpoint, the resultant region might be arbitrary. The boundary of the
          region consists of end-connected curves where each point shares only two edges.
          AutoCAD rejects all intersections and self-intersecting curves.

          Command: _region
          Select objects: 1 found
          Select objects:

          1 loop extracted.
          1 Region created.

  6.      Create two separate drawing files each with the polygon and circle. One of the drawing files will be
          used in subsequent steps.

  7.      EXTRUDE the outside polygon using the “Solid-Extrude” tool.
          Command: extrude



AutoCAD                                       Regions and Solids                           CAD Fundamentals II
                                                       3


       Current wire frame density:      ISOLINES=4

       Select objects: 1 found
       Select objects:

       Specify height of extrusion or [Path]: 3"
       Specify angle of taper for extrusion <0>:


       You can extrude closed polylines, polygons, circles, ellipses, closed splines, donuts, and
       regions. You cannot extrude objects contained within a block. Polylines that have crossing
       or self-intersecting segments cannot be extruded.

       A polyline must contain at least 3 but not more than 500 vertices. If a selected polyline
       has width, AutoCAD ignores the width and extrudes from the center of the polyline path. If
       a selected object has thickness, AutoCAD ignores the thickness.

  8.   EXTRUDE the inside circle. Make the resultant cylinder shorter than the prismed polygon.

  9.   Raise the inside cylinder so that its top coincides with the top of the outside prism.




Set Operations

 10.   SUBTRACT (“Subtract” tool from the “Solids Editing” toolbar) the cylinder from the outside prism.
       Command: subtract
       Select solids and regions to subtract from ..

       Select objects: 1 found

       Select objects:
       Select solids and regions to subtract ..
       Select objects: 1 found

 11.   Draw an axonometric view of the extruded shapes.

 12.   Remove hidden lines and plot.

Regions

 13.   OPEN the other drawing file.

 14.   SUBTRACT the circle from the outer polygon.

 15.   Sketch a new closed polygon (PLINE) next to the existing region, but not touching.

 16.   Convert the new polygon to a region and UNION the two regions.

Sculpting



CAD Fundamentals II                          Regions and Solids                                     AutoCAD
                                                      4



 17.   EXTRUDE the resultant region into a solid.

 18.   Create a rectangle inside the top face of the solid. Set the UCS to the top face before sketching.

 19.   EXTRUDE the rectangle down into the original solid.

 20.   SUBTRACT the extruded rectangle from the original solid.




Use of UCS

 21.   Set the UCS to one of the side faces of the solid.

 22.   Create a solid BOX.

 23.   UNION the box with the solid.

 24.   Set the UCS to another face.

 25.   Create a polygon on the face. Use POLYLINE to create a closed polygon and convert it to a region.

 26.   EXTRUDE the region and UNION to the solid.

 27.   HIDE and plot a two-point perspective of the solid.




                                       Choose an “edge-on” elevation




AutoCAD                                     Regions and Solids                          CAD Fundamentals II
                                                        5




                              In “Orbit” mode, set the projection to “Perspective”
                                    and the “Shading Modes” to “Hidden.”




                                     You will get a two-point perspective.


 28.   Compute the mass properties of your solid, write the results to a file, and print the file.

       Command: massprop
       Select objects: <pick the solids>
       Write to a file <N>: Y

 29.   Round at least one edge of your solid. The FILLET command performs edge rounding when a solid is
       selected and allows the selection of one or more edges to be rounded together.

 30.   Create a SLICE and SECTION of your solid and plot and label each.




                                    Using a rectangle to slice some cubes.




CAD Fundamentals II                          Regions and Solids                                      AutoCAD
                                                      6




                       The top half of the cubes were kept (the bottom sliced away).


       Command: slice
       Select objects: 1 found
       Select objects: 1 found, 2 total
       Select objects: 1 found, 3 total
       Select objects: 1 found, 4 total
       Select objects: 1 found, 5 total
       Select objects: Specify first point on slicing plane by
       [Object/Zaxis/View/XY/YZ/ZX/3points] <3points>: o
       Select a circle, ellipse, arc, 2D-spline, or 2D-polyline:
       Specify a point on desired side of the plane or [keep Both sides]:

       Command:




 31.   Experiment with the effects of the following system variables:

       Plot two views, one with DISPSILH on (1) and one with it off (0).

       ISOLINES - Specifies the number of isolines per surface on objects. Valid integer values
       are from 0 to 2047. The ISOLINES system variable controls the number of tessellation
       lines used to visualize curved portions of the wireframe.
       Command: isolines
       Enter new value for ISOLINES <4>: 6

       FACETRES - Further adjusts the smoothness of shaded and rendered objects and
       objects with hidden lines removed. Valid values are from 0.01 to 10.0.
       Command: facetres
       Enter new value for FACETRES <0.5000>: 1.2

       FACETRATIO - controls the aspect ratio of faceting for cylindrical and conic solids. A
       setting of 1 increases the density of the mesh which can improve the quality of rendered
       and shaded models.
       Command: facetratio
       Enter new value for FACETRATIO <0>: 1




AutoCAD                                     Regions and Solids                         CAD Fundamentals II
                                                     7


       DISPSILH - If the DISPSILH variable is ON, the HIDE command will display solid objects
       with silhouette edges only. It won't show the internal edges produced by facetting the
       object.
       Command: dispsilh
       Enter new value for DISPSILH <0>: 1

 32.   Create a solid of revolution from the region created with the SECTION operation. Set DISPSILH on
       and HIDE and plot.




       Command: isolines
       Enter new value for ISOLINES <4>: 6

       Command: dispsilh
       Enter new value for DISPSILH <0>: 1

       Command: facetres
       Enter new value for FACETRES <0.5000>: 5

       Command: revolve
       Current wire frame density: ISOLINES=6
       Select objects: 1 found
       Select objects:
       Specify start point for axis of revolution or
       define axis by [Object/X (axis)/Y (axis)]:
       Specify endpoint of axis:
       Specify angle of revolution <360>: 90

       Command:

 33.   Using solids, model two mechanical parts chosen from the figure below.

       Round (use the Fillet command with a small radius) all the edges as shown in the figure. Note: it may
       be impossible to round them all. Just do as many as you can. You must round some of the edges.
       Keep the rounding radius small, but visible.

 34.   OR, choose the new “Turner House” and create a massing model using the 3D Solid tools. Keep the
       detail of the model simple so that the amount of effort is similar to step 33.

       Make sure you create a base for your model. You will render this model in a later
       assignment. Remember that drawings with complex solid operations can get potentially
       very large. Make sure you work with your drawing file on the hard disk, and save your
       work often.

       Make at least two axonometric views of your solid models. HIDE and plot.

       The AutoCAD drawing of 1906 Dunmore is on the course web page.




CAD Fundamentals II                        Regions and Solids                                      AutoCAD
                  8




AutoCAD   Regions and Solids   CAD Fundamentals II