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Exploding 3D objects

The EXPLODE command has a particular effect that varies according to the type of 3D object. Table 24-4 lists the effects of exploding 3D objects.

	Table 24-4: Using EXPLODE on 3D Objects
	Object	Result
	Solids	Flat surfaces become regions; curved surfaces become bodies
	Bodies	Curved surfaces become single-surface bodies; flat bodies become
		regions or curves
	Polyface meshes	3D faces
	Polygon meshes	3D faces
	Polylines with thickness	Lines
Note
	A body is a free-form solid. You cannot directly create a body. AutoCAD uses bodies when 3D
	models do not fit into any other object type.

ACIS and stereolithography (.stl) are two file formats especially applicable to 3D models. Chapter 27 explains how to export drawings in these formats.

Editing Solids

Prior to AutoCAD 2000, direct editing of solids was very limited. You could chamfer, fillet, slice, or explode a solid. You could also use UNION, SUBTRACT, and INTERSECT. Other editing commands did not actually modify the solids. AutoCAD 2000 introduced SOLIDEDIT to directly edit solids. This command has so many options that it might as well be several commands.

SOLIDEDIT offers three major types of solid editing:

Faces: A number of options enable you to edit the faces of solids. You can extrude, move, rotate, offset, taper, delete, copy, and color (assign a color to) faces.

Edges: You can color and copy edges.

Bodies: The body options apply to solids as a whole. You can imprint, separate, shell, clean, and check solids. These options are more easily done than said.

The easiest way to use SOLIDEDIT is to open the Solids Editing toolbar and forget the labyrinthine command line.

The next three sections explain how to edit faces, edges, and bodies.

Editing faces

A face is a surface on a solid. A face can be either flat or curved. For example, a hole in a block is a face and many of the face editing operations work well to modify holes. Of course, you can edit an outer face of a surface as well.

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The SOLIDEDIT command supports several methods of selecting a face or faces. You’re accustomed (by now) to selecting a solid by picking one of its edges. However, an edge borders on two faces, and when you pick an edge AutoCAD highlights both its adjoining faces, as shown in Figure 24-40.

Pick point on edge

Figure 24-40: When you pick an edge in the SOLIDEDIT command, AutoCAD selects its two adjoining faces.

Sometimes, picking a face on an edge works — for example, when you want to pick the entire face represented by a hole.

For other situations, to enable you to pick only one face, you can use the boundary set method, by picking within the closed boundary of a face. Generally, AutoCAD selects the front-most face. You can also use a crossing window, crossing polygon, or fence to select a face. For these three latter selection methods, you need to type c, cp, or f, respectively, and then press Enter.

Because selecting the right face can be difficult on a first try, especially for a complex solid, SOLIDEDIT offers plenty of opportunity for correction. After choosing the type of solid editing you want, AutoCAD displays the Select faces or [Undo/Remove]: prompt. Right-click and choose Undo to undo your last selection operation. Right-click and choose Remove to select a face to remove from the selection set. The prompt then includes an Add option that you can use to start adding faces again. You may have to remove and add faces more than once to get the result you want. Then press Enter to end face selection.

You may want to perform more than one operation on a face. After you complete an operation, you can right-click to open the shortcut menu and choose another operation. To exit the command, right-click and choose Exit twice.

Extruding faces

Extruding a face is like extruding a 2D object. If you’re familiar with the EXTRUDE command, you’ll feel comfortable extruding faces. To extrude a face, follow these steps:

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1.Choose Extrude Faces on the Solids Editing toolbar. AutoCAD starts the SOLIDEDIT command and automatically enters the first two prompts of the

command for you.

2.At the Select faces or [Undo/Remove]: prompt, select the face or faces you want to extrude, using the selection method(s) explained previously. After your first selection, the prompt adds the ALL option. When you’re done, press Enter to end face selection.

3.At the Specify height of extrusion or [Path]: prompt, type a height or rightclick and choose Path to specify a path for the extrusion.

4.If you specify a height, at the Specify angle of taper for extrusion <0>: prompt, specify an angle. (As with the EXTRUDE command, a positive angle tapers inward.) If you choose the Path option, at the Select extrusion path: prompt, select an object, usually a line or arc, to extrude along.

5.To extricate yourself from the command, press Enter twice.

You can also use the eXit option that appears on the command line.

AutoCAD extrudes the face. As you exit, AutoCAD performs a validation of the solid to make sure the solid is a valid solid if the SOLIDCHECK system variable is on. By default, SOLIDCHECK is on (set to 1) and automatically checks solids when you edit them.

Moving faces

You can move a face when a solid is complex enough to have at least two separate elements — for example, a plate with a hole in it. You can then move the hole around wherever you want. Look at the mounting bracket in Figure 24-36, earlier in this chapter. You could move the hole from the left face to the right face using SOLIDEDIT. To move a face, follow these steps:

1.Choose Move Faces on the Solids Editing toolbar. AutoCAD starts the SOLIDEDIT command and automatically enters the first two prompts of the command for you.

2.Select the face or faces you want to move, using the selection method(s) described earlier. Press Enter to end face selection.

3.At the Specify a base point or displacement: prompt, specify a base point if you want to pick two points, or specify a displacement, as you would with the MOVE command.

4. At the Specify a second point of displacement: prompt, specify a second point of displacement if you specified a base point. Otherwise, press Enter.

5. Right-click and choose Enter twice to exit the command.

If you choose a face that cannot be moved, AutoCAD displays the Modeling Operation Error: No solution for an edge message.

Offsetting faces

You can offset a face when a solid has two separate elements, such as a wall with a window cut out of it. You can then resize the window by offsetting it. Offsetting a face increases all parts of the face equally by a distance you specify.

Use a positive offset value to increase the volume of the solid. If your face is a solid axle in the middle of a disk, for example, and you offset the axle with a positive value, the axle gets bigger. However, if your face is a hole in the middle of a disk, a positive offset value makes the hole smaller because that makes the resulting solid bigger.

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Use a negative offset value to decrease the volume of the solid. Using the same example, a negative offset value would make the axle smaller, but it would make the hole bigger.

To offset a face, follow these steps:

1.Choose Offset Faces from the Solids Editing toolbar. AutoCAD starts the SOLIDEDIT command and automatically enters the first two prompts of the

command for you.

2.Select the face or faces you want to offset and press Enter to end face selection.

3.At the Specify the offset distance: prompt, type a positive or negative distance. You can also pick two points to specify a positive offset.

4.Right-click and choose Enter twice to exit the command.

AutoCAD offsets the face. If there is no room for the offset, AutoCAD displays the message

Modeling Operation Error on the command line.

Deleting faces

You can delete a face of a solid. This is a great way to instantly get rid of a hole, axle, or window within a solid. You can delete faces to undo the effects of both the UNION and SUBTRACT commands. You can also remove filleted and chamfered faces. AutoCAD won’t delete every face; for example, you can’t turn a box into a tetrahedron by deleting the box’s top face. However, the capability to delete faces is a very powerful tool for editing your solids.

To delete a face or faces, choose Delete Faces from the Solids Editing toolbar. Select the face or faces and press Enter. AutoCAD deletes the face or faces you selected. If your

face(s) can’t be deleted, you see the message Modeling Operation Error on the command line.

Rotating faces

You can rotate a face when a solid is complex enough to have at least two separate elements — for example, a box with a hole in it. The prompts for rotating are very similar to those for ROTATE3D, covered earlier in this chapter. To rotate a face, follow these steps:

1.Choose Rotate Faces on the Solids Editing toolbar. AutoCAD starts the SOLIDEDIT command and automatically enters the first two prompts of the command for you.

2.Select the face or faces you want to rotate, using the selection method(s) described earlier. Press Enter to end face selection.

3.At the Specify an axis point or [Axis by object/View/Xaxis/Yaxis/Zaxis] <2points>: prompt, specify the first point of a rotation axis or use one of the options to define an axis of rotation.

4.If you specified a first point, at the Specify the second point on the rotation axis: prompt, specify the second point.

5.At the Specify a rotation angle or [Reference]: prompt, specify a rotation angle (the right-hand rule applies in determining the direction of rotation) or use the Reference option to specify a reference (starting) angle, and then an ending angle.

6.Right-click and choose Enter twice to exit the command.

AutoCAD rotates the face. If you choose a face that cannot be rotated, or if there isn’t room on the solid for the rotation, AutoCAD lets you know with the message Modeling Operation Error on the command line.

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Tapering faces

You can taper an entire simple solid, such as a box, or you can taper a face that is an element within a complex solid, such as a hole or an axle. Tapering angles the sides of the face. To determine the direction of the taper, that is, which end gets tapered, you specify a base point and a second point. The base point side of the solid is not tapered, and AutoCAD tapers the face in the direction from the base point toward the second point. You also specify the angle of the taper. A positive taper angle tapers the face inward; a hole is tapered outward. A negative taper angle tapers the face outward; a hold is tapered inward. Figure 24-41 shows a box before and after tapering at a 15-degree angle, as well as the base point and second points that were used. All the faces except the bottom were selected.

In general, use small tapering angles. If the face would taper to a point before it reaches its existing height, AutoCAD cannot complete the taper.

Second point

Base point

Figure 24-41: A box before and after tapering at a 15-degree angle.

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To taper a face, follow these steps:

1.Choose Taper Faces on the Solids Editing toolbar. AutoCAD starts the SOLIDEDIT command and automatically enters the first two prompts of the command for you.

2.Select the face(s) you want to taper. Press Enter to end face selection.

3.At the Specify the base point: prompt, pick the base point for the taper direction. Object snaps are a good idea.

4.At the Specify another point along the axis of tapering: prompt, specify a second point to indicate the direction of the taper. Again, use an object snap.

5.At the Specify the taper angle: prompt, specify an angle between –90° and +90°.

6.Right-click and choose Enter twice to exit the command.

AutoCAD tapers the face. If AutoCAD can’t taper the face, you see the message Modeling Operation Error on the command line.

Copying faces

You can copy any face, including a hole. AutoCAD creates regions or bodies out of the face. You can then use the EXTRUDE command to extrude one region. However, if you copy a complex face, such as a hole that may consist of several regions, you can’t turn it back into a solid again.

To copy a face, follow these steps:

1.Choose Copy Faces from the Solids Editing toolbar. AutoCAD starts the SOLIDEDIT command and automatically enters the first two prompts of the command for you.

2.Select the face(s) you want to copy. Press Enter to end face selection.

3.At the Specify a base point or displacement: prompt, specify a base point. Object snaps are helpful.

4. At the Specify a second point of displacement: prompt, specify a second point to indicate the direction and distance for the copy.

5. Right-click and choose Enter twice to exit the command.

AutoCAD copies the face.

Coloring faces

You can assign a color to a face of an object. You might want to color a face to make it easier to see. You can also color a face so that you can assign a material to it (you can assign materials by color) for the purpose of rendering. The color overrides the color setting for the solid’s layer.

Note When an object is assigned more than one material, priority goes to attachment by object, then by color, and finally by layer. If you attach a material to a solid by layer, and then attach a material to one of its faces (that you have colored) by color, both the solid and the face display their materials. For more information, see Chapter 25.

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To color a face, follow these steps:

1.Choose Color Faces from the Solids Editing toolbar. AutoCAD starts the SOLIDEDIT command and automatically enters the first two prompts of the command for you.

2.Select the face or faces you want to color. Press Enter to end face selection.

3.AutoCAD opens the Select Color dialog box. Choose a color and click OK.

4.Right-click and choose Enter twice to exit the command.

AutoCAD colors the face.

On the	The drawing used in the following Step-by-Step exercise on editing solid faces, ab24-11.
CD-ROM	dwg, is in the Results folder on the CD-ROM.

STEP-BY-STEP: Editing Solid Faces

1.Open ab24-11.dwg from the Results folder of the CD-ROM. If you did the exercise on filleting solids, you can open it from your AutoCAD Bible folder.

2.Save the file as ab24-13.dwg in your AutoCAD Bible folder.

3.If the Solids Editing toolbar is not displayed, right-click any toolbar and choose Solids Editing. This is a mounting bracket, shown in Figure 24-42. Note the UCS icon, which is at 0,0,0.

2 1

3

Figure 24-42: The mounting bracket.

4.Make sure OSNAP is on. Set a running object snap for midpoint.

5. Choose Offset Faces from the Solids Editing toolbar.

6.At the Select faces or [Undo/Remove]: prompt, select the slot in the mounting angle. Selecting the slot may require a few picks to make sure that all the parts of the slot are highlighted and to remove from selection the unwanted faces of the mounting bracket that become highlighted. (Hint: Try picking on the cross-lines that connect the front and back of the slot.) To remove a face, right-click and choose Remove. Then pick on a face’s edge. To add faces again, right-click and choose Add. After you’re done, press Enter (or right-click and choose Enter) to end face selection.

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7.At the Specify the offset distance: prompt, type .1 . AutoCAD makes the slot smaller.

8.You’re still in the SOLIDEDIT command. Right-click and choose Taper. At the next prompt, select the slot and press Enter after you’re done selecting.

9.At the Specify the base point: prompt, pick the midpoint at 1.

10.At the Specify another point along the axis of tapering: prompt, pick the midpoint at 2.

11.At the Specify the taper angle: prompt, type 10 . AutoCAD tapers the slot.

12.Right-click and choose Delete. At the next prompt, select the filleted face at 3. Rightclick and choose Enter. AutoCAD removes the fillet.

13.Right-click and choose Extrude. At the next prompt, select the face at 3 by picking inside the face. Right-click and choose Enter.

14.At the Specify height of extrusion or [Path]: prompt, type .2 .

15.At the Specify angle of taper for extrusion <0>: prompt, type 10 . AutoCAD extrudes the face.

16.Right-click and choose Enter twice to exit the command.

17.Save your drawing. It should look like Figure 24-43.

Figure 24-43: The edited mounting angle.

Editing edges

The two-dimensional place where two faces meet is an edge. You can perform only two editing operations on edges — you can copy them and color them.

Copying edges

When you copy an edge, you get a line, arc, circle, ellipse, or spline, depending on the shape of the solid’s edge. To copy an edge, follow these steps:

1.Choose Copy Edges from the Solids Editing toolbar. AutoCAD starts the SOLIDEDIT command and automatically enters the first two prompts of the command for you.

2.Select the edge or edges you want to copy.

740 Part IV Drawing in Three Dimensions

3.At the Specify a base point or displacement: prompt, specify a base point, preferably using an object snap or a displacement.

4. At the Specify a second point of displacement: prompt, specify a second point or press Enter if you specified a displacement in Step 2.

5. Right-click and choose Enter twice to exit the command.

AutoCAD copies the edge or edges.

Coloring edges

You can color an edge to make it more visible. The color overrides the color setting for the solid’s layer. To color an edge, follow these steps:

1.Choose Color Edges from the Solids Editing toolbar. AutoCAD starts the SOLIDEDIT command and automatically enters the first two prompts of the command for you.

2.Select the edge or edges you want to color. Press Enter to end edge selection.

3.AutoCAD opens the Select Color dialog box. Choose the color you want and click OK.

4.Right-click and choose Enter twice to exit the command.

AutoCAD colors the edge.

Editing bodies

Several of the SOLIDEDIT options apply to solids as a whole. The operations available are imprinting, cleaning, separating, shelling, and checking. Each operation is discussed in the following sections.

Imprinting solids

You can imprint an arc, circle, line, 2D polyline or 3D polyline, ellipse, spline, region, body, or 3D solid on a solid. The object you’re imprinting must intersect a face on the solid. The shape made by the intersection of the object is left on the solid, as if you put ink on the edges of the object and stamped it on the solid. Figure 24-44 shows an example of imprinting.

Figure 24-44: The ellipse was drawn on the top of the solid. After imprinting and deleting the ellipse, the shape of half the ellipse remains on the solid.

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To imprint a solid, follow these steps:

1.First create one of the stampable objects previously listed so that it intersects with a solid. If you draw in top view, check in an isometric view to make sure the intersection is where you want it.

2.Choose Imprint from the Solids Editing toolbar. AutoCAD starts the SOLIDEDIT command and automatically enters the first two prompts of the command for you.

3.At the Select a 3D solid: prompt, select a solid. You can select only one.

4. At the Select an object to imprint: prompt, select the object you want to imprint.

5. At the Delete the source object [Yes/No] <N>: prompt, type y or press Enter to indicate No.

6.AutoCAD repeats the Select an object to imprint: prompt. You can continue the command in the same way or press Enter if you’re done.

7.Right-click and choose Enter twice to exit the command.

AutoCAD imprints the solid. If you didn’t delete the source object, you’ll need to move it to see the result.

Cleaning solids

After all the editing, you can end up with some pretty strange solids. Cleaning solids removes imprints as well as adjacent faces that share the same surface.

To clean a solid, choose Clean from the Solids Editing toolbar. At the Select a 3D solid: prompt, select a solid. AutoCAD cleans it.

Separating solids

You can separate a solid that is made up of more than one completely separate section. You would generally create such a solid from separate, nontouching solids, using the UNION command. The Separate option undoes the effect of the UNION command so that the solids become separate again. You can compare this operation to grouping and ungrouping objects (see Chapter 18).

To separate a solid, choose Separate from the Solids Editing toolbar. At the Select a 3D solid: prompt, select the solid by picking any of its sections. AutoCAD separates

the solids.

If your solid sections are even touching, you get one of the funnier AutoCAD messages: The selected solid does not have multiple lumps.

Shelling solids

When you shell a solid, you hollow out its inside, leaving a thin wall. Think of making a drinking glass from a truncated cone (or tapered cylinder) or a room from a solid box. Shelling is a common process in high-end 3D modeling programs. To shell a solid, follow these steps:

1.Choose Shell from the Solids Editing toolbar. AutoCAD starts the SOLIDEDIT command and automatically enters the first two prompts of the command for you.

2.Select a solid.

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3.At the Remove faces or [Undo/Add/ALL]: prompt, remove any face or faces that you don’t want to shell. For example, if you’re making a drinking glass from a truncated cone, you want to remove the larger circular face (the one you would drink out of) so that it will remain open. Otherwise, you end up with an enclosed solid that has a hollow interior. After you finish removing faces, press Enter. (The command line confirms 1 face found, 1 removed, but there is no obvious confirmation that AutoCAD has removed the correct face.)

4.At the Enter the shell offset distance: prompt, type the width of the wall you want to create. A positive value creates a shell to the inside of the current solid. A negative value creates a shell to the outside of the current solid.

5.Right-click and choose Enter twice to exit the command.

AutoCAD shells the solid.

Checking solids

Checking ensures that your solid is a valid 3D solid object so that you can edit it without getting ACIS failure error messages. This might be a useful feature to put into an AutoLISP or VBA program, to make sure that it doesn’t fail because of invalid solids.

To check a solid, choose Check from the Solids Editing toolbar. At the Select a 3D solid: prompt, select a solid. Usually, AutoCAD replies with the message: This object

is a valid ShapeManager solid.

On the	The drawing used in the following Step-by-Step exercise on editing solid bodies,
CD-ROM	ab24-j.dwg, is in the Drawings folder on the CD-ROM.

STEP-BY-STEP: Editing Solid Bodies

1.Open ab24-j.dwg from the CD-ROM.

2.Save the file as ab24-14.dwg in your AutoCAD Bible folder. This is a simple solid box with an ellipse drawn on part of its top face.

3.Choose Imprint from the Solids Editing toolbar. Follow the prompts:

Select a 3D solid: Select the box.

Select an object to imprint: Select the ellipse. Delete the source object [Yes/No] <N>: y . Select an object to imprint: Right-click.

4.Right-click and choose Clean. At the Select a 3D solid: prompt, select the box.

5.Right-click and choose Shell. Follow the prompts:

Select a 3D Solid: Select the box.

Remove faces or [Undo/Add/ALL]: Pick anywhere inside the top face.

Remove faces or [Undo/Add/ALL]: Right-click and choose Enter. Enter the shell offset distance: .1

6.Press Enter twice to exit the command.

7.Choose View Hide. You can now see the result of the shell operation.

8.Save your drawing. It should look like Figure 24-45.