In the first set of exercises, you'll draw a chair that you can later add to your 3D unit drawing. In drawing this chair, you'll be exposed to the UCS as well as to some of the other 3D capabilities available in AutoCAD:

Notice that the UCS icon appears in the same plane as the current coordinate system. The icon will help you keep track of which coordinate system you're in. Now you can see the chair components as 3D objects.

Next, you'll define a UCS that is aligned with one side of the seat:

The Orthographic UCSs tab offers a set of predefined UCSs for each of the six standard orthographic projection planes. Figure 22.4 shows these UCSs in relation to the WCS.

Because a good part of 3D work involves drawing in these orthographic planes, AutoCAD supplies the ready-made UCS orientations for quick access. But you aren't limited to these six orientations. If you're familiar with mechanical drafting, you'll see that the orthographic UCSs correspond to the typical orthographic projections used in mechanical drafting. If you're an architect, the Front, Left, Back, and Right UCSs correspond to the south, west, north, and east elevations of a building.

Before you continue building the chair model, you'll move the UCS to the surface on which you'll be working. Right now, the UCS has its origin located in the same place as the WCS origin.

You can move a UCS so that its origin is anywhere in the drawing where it's needed:

Figure 22.5. Setting up a UCS

You just created a new UCS based on the Front UCS you selected from the UCS dialog box. Now, as you move your cursor, the origin of the UCS icon corresponds to a 0,0 coordinate. Although you have a new UCS, the WCS still exists; you can always return to it when you need to.

After you've gone through the work of creating a UCS, you may want to save it, especially if you think you'll come back to it later. Here's how to save a UCS:

Your UCS is now saved with the name 3DSW. You can recall it from the UCS dialog box or by using other methods that you'll learn about later in this chapter.

Next, you'll arrange the seat and back and draw the legs of the chair. Your UCS is oriented so that you can easily adjust the orientation of the chair components. As you work through the next exercise, notice that although you're manipulating 3D objects, you're really using the same tools you've used to edit 2D objects.

Follow these steps to adjust the seat and back and to draw legs:

Figure 22.7. The chair after rotating and moving the components

The new UCS orientation enabled you to use the grips to adjust the chair seat and back. All the grip rotation in the previous exercise was confined to the plane of the new UCS. Mirroring and scaling will also occur in relation to the current UCS.

As you work in 3D, your models will become fairly complex. When your model becomes too crowded for you to see things clearly, it helps to build parts of the model and then import them instead of building everything in one file. In the next set of exercises, you'll draw the legs of the chair and then import them to the main chair file to give you some practice in the procedure.

I've prepared a drawing called legs.dwg, which consists of two polylines that describe the shape of the legs. I did this to save you some tedious work that isn't related to 3D modeling. You'll use this file as a starting point for the legs, and then you'll import the legs into the barcelona1.dwg file:

Next, you need to change the Thickness property of the two polylines to make them 2″ or 5 cm wide:

Figure 22.8. Move the legs so they meet the chair seat at the corner indicated.

As you've just seen, you can convert polylines that have both a width and a thickness into 3D solids. Now you're ready to add the legs to the rest of the chair.

In these last few exercises, you worked on the legs of the chair in a separate file and then imported them into the main chair file with a click-and-drag motion. By working on parts in separate files, you can keep your model organized and more manageable. You may have also noticed that although the legs were drawn in the WCS, they were inserted in the 3DSW UCS that you created earlier. This shows you that imported objects are placed in the current UCS. The same would have happened if you inserted an Xref or another file.

You can define a UCS based on the orientation of an object. This is helpful when you want to work on a predefined object to fill in details on its surface plane. The following steps are for information only and aren't part of the tutorial. You can try this at another time when you aren't working through an exercise.

Follow these steps to define a UCS this way:

Figure 22.10. Using the Object option of the UCS command to locate a UCS

When you create a UCS using the Object option, the location of the UCS origin and its orientation depend on how the selected object was created. Table 22.1 describes how an object can determine the orientation of a UCS.

At times, you may want to work in a UCS that has the same orientation as the current UCS but is offset. For example, you might be drawing a building that has several parallel walls offset with a sawtooth effect (see Figure 22.11).

Another UCS option, called Move, will move an existing, named UCS to a new location and keep its original orientation. You won't find the UCS Move option on any panel or toolbar, but you can use it by entering UCS

Figure 22.11. Using the Origin option to shift the UCS

The steps in the following section are for information only and aren't part of the tutorial. You can try this at another time when you aren't working through an exercise.

Suppose you want to change the orientation of the X, Y, or Z axis of a UCS. You can do so by using the X, Y, or Z Axis Rotate UCS option on the View tab's Coordinates panel. These are perhaps one of the most frequently used UCS options:

Figure 22.12. Rotating the UCS about the Z axis

Similarly, the X and Y Axis Rotate UCS options enable you to rotate the UCS about the current X and Y axis, respectively, just as you did for the Z axis earlier. The X and Y Axis Rotate UCS tools are helpful in orienting a UCS to an inclined plane. For example, if you want to work on the plane of a sloped roof of a building, you can first use the Origin UCS tool to align the UCS to the edge of a roof and then use the X Axis Rotate UCS tool to rotate the UCS to the angle of the roof slope, as shown in Figure 22.13. Note that the default is 90°, so you only have to press

Figure 22.13. Moving a UCS to the plane of a sloping roof

Finally, you align the Z axis between two points using the Z Axis Vector option. This is useful when you have objects in the drawing that you can use to align the Z axis. Here are the steps:

Because your cursor location is in the plane of the current UCS, it's best to pick a point on an object by using either the Osnap overrides or the coordinate filters.

Figure 22.14. Picking points for the Z Axis Vector option

Finally, you can define a UCS in the current view plane. This is useful if you want to switch quickly to the current view plane for editing or for adding text to a 3D view.

AutoCAD uses the current UCS origin point for the origin of the new UCS. By defining a view as a UCS, you can enter text to label your drawing, just as you would in a technical illustration. Text entered in a plane created this way appears normal.

You've finished your tour of the UCS command. Set the UCS back to the WCS, and save the Barcelona1.dwg file.

You've explored nearly every option in creating a UCS except one. Later on in this chapter, you'll learn about the 3 Point option for creating a UCS. This is the most versatile method for creating a UCS, but it's more involved than some of the other UCS options.

AutoCAD has the ability to save a UCS with a view. Click the View Manager option, found at the top of the View drop-down list in the Home tab's View panel (Figure 22.15). At the View Manager dialog box, click the New button. This opens the New View/Shot Properties dialog box. Enter a name for your new view in the View name input box, and then choose a UCS to save with a new view by using the UCS drop-down list located in the Settings group of the dialog box.

Figure 22.15. Select the View Manager option in the View dropdown list.

In this next group of exercises, you'll draw a butterfly chair. This chair has no perpendicular or parallel planes to work with, so you'll start by setting up some points that you'll use for reference only. This is similar in concept to laying out a 2D drawing. As you progress through the drawing construction, notice how the reference points are established to help create the chair. You'll also construct some temporary 3D lines to use for reference. These temporary lines will be your layout. These points will define the major UCSs needed to construct the drawing. The main point is to show you some of the options for creating and saving UCSs.

To save time, I've created the 2D drawing that you'll use to build your 3D layout. This drawing consists of two rectangles that are offset by 4″ (10 mm for metric users). To make it more interesting, they're also off center from each other (see Figure 22.23).

Figure 22.23. Setting up a layout for a butterfly chair

The first thing you'll need to do is set up the drawing for the layout:

Figure 22.24. Click SW Isometric in the View dropdown list.

Now you need to move the outer rectangle in the Z axis so its elevation is 30″ (76 cm for metric users):

As an alternate method in step 3, after choosing Move from the Grip Edit shortcut menu, you can turn on Ortho mode and point the cursor vertically so it shows -Z in the coordinate readout. Then enter 30

In the previous exercise, you used relative Cartesian coordinates to locate the second point for the Move command. For commands that accept 3D input, you can also specify displacements by using the Spherical and Cylindrical Coordinate formats.

The Spherical Coordinate format lets you specify a distance in 3D space while specifying the angle in terms of degrees from the X axis of the current UCS and degrees from the X-Y plane of the current UCS (see the top image in Figure 22.26). For example, to specify a distance of 4.5″ (11.43 cm) at a 30° angle from the X axis and 45° from the X-Y plane, enter @4.5<30<45 (or @11.43<30<45 for metric users). This refers to the direct distance followed by a < symbol, then the angle from the X axis of the current UCS followed by another < symbol, and then the angle from the X-Y plane of the current UCS. To use the Spherical Coordinate format to move the rectangle in the exercise, enter @30<0<90 at the Second point: prompt, or @76<0<90 for metric users.

Figure 22.26. The Spherical and Cylindrical Coordinate formats

The Cylindrical Coordinate format, on the other hand, lets you specify a location in terms of a distance in the plane of the current UCS and a distance in the Z axis. You also specify an angle from the X axis of the current UCS (see the top image in Figure 22.26). For example, to locate a point that is a distance of 4.5″ (11.43 cm) in the plane of the current UCS at an angle of 30° from the X axis and a distance of 3.3″ (8.38 cm) in the Z axis, enter @4.5<30,3.3 (or @11.43<30,8.38 for metric users). This refers to the distance of the displacement from the plane of the current UCS followed by the < symbol, then the angle from the X axis followed by a comma, and then the distance in the Z axis. Using the Cylindrical Coordinate format to move the rectangle, you enter @0<0,30 at the Second point: prompt, or @0<0,76 for metric users.

Now you'll draw the legs for the butterfly chair by using a 3D polyline. This is a polyline that can be drawn in 3D space. Here are the steps:

All objects, with the exception of lines and 3D polylines, are restricted to the plane of your current UCS. Two other legacy 3D objects, 3D faces and 3D meshes, are also restricted. You can use the Pline command to draw polylines in only one plane, but you can use the 3DPoly command to create a polyline in three dimensions. 3DPoly objects can't, however, be given thickness or width.

Next, you'll draw the seat of the chair. The seat of a butterfly chair is usually made of canvas, and it drapes from the four corners of the chair legs. You'll first define the perimeter of the seat by using arcs, and then you'll use the Edge Surface tool on the Home tab's expanded Modeling panel to form the shape of the draped canvas. The Edge Surface tool creates a surface based on four objects defining the edges of that surface. In this example, you'll use arcs to define the edges of the seat.

To draw the arcs defining the seat edges, you must first establish the UCSs in the planes of those edges. In the previous example, you created a UCS for the side of the chair before you could draw the legs. In the same way, you must create a UCS defining the planes that contain the edges of the seat.

Because the UCS you want to define isn't orthogonal, you'll need to use the three-point method. This lets you define the plane of the UCS based on three points:

You've defined and saved a UCS for the front side of the chair. As you can see from the UCS icon, this UCS is at a non-orthogonal angle to the WCS. Continue by creating UCSs for two more sides of the butterfly chair:

Next, you'll mirror the side-edge spline to the opposite side. This will save you from having to define a UCS for that side:

Figure 22.30. Set your UCS to World, and then mirror the arc that defines the side of the chair seat.

Figure 22.31. Your butterfly chair so far

Quick Hops to Your Ucss

If you find you're jumping from one saved UCS to another, you'll want to know about the UCS Combo Control drop-down list. This list is located in the View tab's Coordinates panel and it contains the World and other standard UCS options as well as all the saved UCSs in a drawing. You can use this list as a quick way to move between UCSs that you've set up or between the predefined orthogonal UCSs.

Another great way to jump quickly between UCSs is to use the UCS Face option. The Face option requires a 3D solid, but once you have one in place, you can choose Face from the View tab's Coordinates panel and then click the face of the solid to which you want to align your UCS. For example, you can use the Loft command (see the section "Shaping the Solid" later in this chapter) to create a solid similar to the solid shown later in Figure 22.35 that connects the top and top rectangles of the butterfly chair. You can then use the UCS Face option to align to the sides of that solid to draw the arcs and polylines for the seat outline. This way, you're using the 3D solid as a layout tool.

Finally, let's finish this chair by adding the mesh representing the chair seat:

Figure 22.32. The butterfly chair so far

You've got the beginnings of a butterfly chair with the legs drawn in schematically and the seat as a 3D surface. You can add some detail by using a few other tools, as you'll see in the next set of exercises.

In the previous example, you used the Loft tool to create a 3D surface. Once you have a surface, you can convert it to a solid to perform other modifications.

You'll want to round the corners of the seat surface to simulate the way a butterfly chair hangs off its frame. You'll also round the corners of the frame and turn the frame into a tubular form. Start by rounding the seat surface. This will involve turning the surface into a solid so you can use solid editing tools to get the shape you want:

You can also enter Thicken

The seat surface appears to lose its webbing, but it has just been converted to a very thin 3D solid.

The butterfly chair is in a fairly schematic state. The corners of the chair are sharply pointed, whereas a real butterfly chair would have rounded corners. In this section, you'll round the corners of the seat with a little help from the original rectangles you used to form the layout frame.

First, you'll use the Fillet command to round the corners of the rectangles. Then, you'll use the rounded rectangles to create a solid from which you'll form a new seat:

Next, create a 3D solid from the two rectangles using the Loft tool:

In this next exercise, you'll use a tool that is intended to find the interference between two solids. This is useful if you're working with crowded 3D models and you need to check whether objects may be interfering with each other. For example, a mechanical designer might want to check to make sure duct locations aren't passing through a structural beam.

You'll use Interfere as a modeling tool to obtain a shape that is a combination of two solids: the seat and the rectangular solid you just created. Here are the steps:

You can also enter interfere

The view shows the interference of the two solids in red. Notice that the corners are rounded on the red interference.

As mentioned earlier, the Interference Checking tool is intended to help you find out whether objects are colliding in a 3D model; as you've just seen, though, it can be an excellent modeling tool that can help you derive a form that you may otherwise not have the ability to create.

A number of other options are available when you're using the Interference Checking tool. Table 22.2 lists the options in the Interference Checking dialog box.

Figure 22.37. The interference solid appears on top of the original seat.

The prompt for the Interference Checking command also showed some options. The prompt in step 2 shows Nested selection/Settings. The Nested selection option lets you select objects that are nested in a block or an Xref. The Settings option opens the Interference Settings dialog box (Figure 22.38).

Figure 22.38. Settings for interference

This dialog box offers settings for the temporary display of interference objects while you're using the Interference command. Table 22.3 lists the options for this dialog box.

One more element needs to be taken care of before your chair is complete. The legs are currently simple lines with sharp corners. In this section, you'll learn how you can convert lines into 3D tubes. To make it more interesting, you'll add rounded corners to the legs.

Start by rounding the corners on the lines you've created for the legs:

The chair is almost complete, but the legs are just wireframes. Next you'll give them some thickness by turning them into tubes. Start by creating a set of circles. You'll use the circles to define the diameter of the tubes:

Now you're ready to form the tubes:

Figure 22.40. A perspective view of the butterfly chair with tubes for legs

Although you used circles with the Sweep command to create tubes, you can use any closed polyline shape. Figure 22.41 gives some examples of other shapes you can use with the Sweep command.

Figure 22.41. You can use any closed shape with the Sweep command.

In step 3 of the previous exercise, you may have noticed some command-line options. These options offer additional control over the way Sweep works. Here is a rundown on how these options work:

These options are available as soon as you select the sweep object and before you select the path object. You can use any combination of options you need. For example, you can apply the Twist and Scale options together, as shown in Figure 22.46.

Figure 22.46. The Scale and Twist options applied together

In the Barcelona chair example, you converted a surface into a solid using the Thicken command. Next, you'll use a surface to create a solid in a slightly different way. This time, you'll use the surface to slice a solid into two pieces. This will give you a form that is more easily read and understood as a terrain model:

Figure 22.51. The box extruded through the contours

You may have noticed that as you raised the box height, you could see how it intersected the contour surface. Next you'll slice the box into two pieces:

Figure 22.53. The box with the contour surface imprinted

In step 3, you saw a prompt that offered a variety of methods for slicing the box. The Surface option allowed you to slice the box using an irregular shape, but most of the other options let you slice a solid by defining a plane or a series of planar objects.

A question I hear frequently from civil engineers is "How can I find the volume of earth from an excavated area?" This is often referred to as a cut from a cut and fill operation. To do this, you first have to create the cut shape. Next, you use the Interfere command to find the intersection between the cut shape and the contour surface. You can then find the volume of the cut shape using one of AutoCAD's inquiry commands. The following exercise demonstrates how this is done.

Suppose that the contour model you've just created represents a site where you'll excavate a rectangular area for a structure. You want to find the amount of earth involved in the excavation. A rectangle has been placed in the contour drawing representing such an area:

With the excavation rectangle in place, you can use the Interfere command to find the volume of the excavation:

As you've seen from the exercises in this chapter, the Loft command lets you create just about any shape you can imagine, from a simple sling to the complex curves of a contour map. If your loft cross sections are a set of closed objects like circles or closed polygons, the resulting object is a 3D solid instead of a surface.

The order in which you select the cross sections is important because Loft will follow your selection order to create the surface or solid. For example, Figure 22.58 shows a series of circles used for a lofted solid. The circles are identical in size and placement, but the order of selection is different. The solid on the left was created by selecting the circles in consecutive order from top to top, creating an hourglass shape. The solid on the right was created by selecting the two larger circles first from top to top; the smaller, intermediate circle was selected last. This selection order created a hollowed-out shape with more vertical sides.

In addition to the selection order, several other settings affect the shape of a solid created by the Loft command. In the contour-map example, you selected a setting in the Loft Settings dialog box (Figure 22.59). This dialog box appears when you select the Cross Section Only option after you've selected a set of cross sections.

Figure 22.58. The order in which you select the cross sections affects the result of the Loft command.

Figure 22.59. Loft Settings: Smooth Fit

You can radically affect the way the Loft command forms a surface or a solid through the options in this dialog box, so it pays to understand what those settings do. Take a moment to study the following sections that describe the Loft Settings dialog box options.

Ruled and Smooth Fit

The Ruled option connects the cross sections with straight surfaces, as shown in the sample to the left in Figure 22.60.

Figure 22.60. Samples of a Ruled loft at left and a Smooth Fit loft on the right

The Smooth Fit option connects the cross sections with a smooth surface. It attempts to make the best smooth transitions between the cross sections, as shown in the right image in Figure 22.60.

Normal To

Normal To is a set of four options presented in a drop-down list. To understand what this option does, you need to know that normal is a mathematical term referring to a direction that is perpendicular to a plane, as shown in Figure 22.61. In these options, Normal refers to the direction the surface takes as it emerges from a cross section.

Figure 22.61. A normal is a direction perpendicular to a plane.

If you use the All Cross Sections option, the surfaces emerge in a perpendicular direction from all the cross sections, as shown in the first image in Figure 22.62. If you use the End Cross Section option, the surface emerges in a direction that is perpendicular to just the end cross section, as shown in the second image in Figure 22.62. The Start Cross Section option causes the surface to emerge in a direction perpendicular to the start cross section. The Start And End Cross Sections option combines the effect of the Start Cross Section and End Cross Section options.

Figure 22.62. Samples of the Normal To options applied to the same set of cross sections

Draft Angles

The Draft Angles option affects only the first and last cross sections. This option generates a smooth surface with added control over the start and end angle. Unlike the Normal To option, which forces a perpendicular direction to the cross sections, Draft Angles allows you to set an angle for the surface direction. For example, if you set Start Angle to a value of 0, the surface will bulge outward from the start cross section, as shown in the first image of Figure 22.63.

Figure 22.63. The Draft Angle options

Likewise, an End Angle setting of 0 will cause the surface to bulge at the end cross section (see the second image in Figure 22.63).

The Start and End Magnitude settings let you determine a relative strength of the bulge. The right image in Figure 22.63 shows a Draft Angle of 0 and magnitude of 50 for the last cross section.

Close Surface or Solid and Preview Changes

The Close Surface Or Solid option is available only when the Smooth Fit option is selected. It causes the first and last cross section objects to be connected so the surface or solid loops back from the last to the first cross section. Figure 22.64 shows the cross sections at the left, a smooth version in the middle, and a smooth version with the Close Surface Or Solid option turned on. The Close Surface option causes the solid to become a tube.

The Preview Changes option lets you see in real time the effects of the Loft Settings dialog box options.

Figure 22.64. The Close Surface Or Solid option connects the end and the beginning cross sections.

In mechanical drawing, you often create the parts in 3D and then show an assembly of the parts. The Align command can greatly simplify the assembly process. The following steps show how to use Align to line up two objects at specific points:

Figure 22.65. Aligning two 3D objects

In Chapter 21, you saw how you can use the grip tool to help restrain the motion of an object in the X, Y, or Z axis. AutoCAD offers a Move command specifically designed for 3D editing that includes a grip tool to restrain motion.

You don't need to perform these steps as an exercise. You can try the command on your own when you need to use it.

Here's how it works:

You can also enter 3dmove

Figure 22.66. The grip tool

The 3D Rotate command is another command that is like an extension of its 2D counterpart. With 3D Rotate, a rotate grip tool appears that restrains the rotation about the X, Y, or Z axis.

You don't need to perform these steps as an exercise. You can try the command on your own when you need to use it.

Here's how it works: