To Learn to Use the Solid Modeling Commands to Create, Manipulate, and Measure Solids

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Objective

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

Exercise:

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

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.

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

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

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.

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.

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.

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.

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.

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: isolines

Enter new value for ISOLINES <4>: 6

Command: facetres

Enter new value for FACETRES <0.5000>: 1.2

Command: facetratio

Enter new value for FACETRATIO <0>: 1

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.

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

Make sure you create a base and at least two distinct solids for your model. You will render this model in a later assignment. Try to round and fillet as many edges as you can. 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.

Round (Fillet – 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.

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

CAD Fundamentals II Regions, Solids and Rendering AutoCAD