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In your work with so far in this chapter, you have simply extruded existing forms, or you have set to draw extruded objects. But extruded forms have their limitations. Using just extruded forms, it’s hard to draw diagonal surfaces in the z-axis. AutoCAD provides the 3D Face object to give you more flexibility in surfaces in three-dimensional space. The 3D Face produces a 3D surface where each comer can be given an x, y, and z value. By using 3D Faces in conjunction with extruded objects, you can create a 3D model of just about anything. When you view these 3D objects in a 2D Plan view, you will see them as 2D objects showing only the x and y positions of their corners or endpoints.

Using Point Filters

Before you start working with 3D surfaces, you should have a good idea of what the z-coordinate values are for your model. The simplest way to construct surfaces in 3D space is to first create some layout lines to help you place the endpoints of 3D Faces.

AutoCAD offers a method for 3D point selection, called filtering, that simplifies the selection of z-coordinates. Filtering allows you to enter an x, y, or z value by picking a point on the screen and telling AutoCAD to use only the x, y, or z value of that point, or any combination of those values. If you don’t specify a z-coordinate, the current elevation setting is assumed.

In the following exercises, let’s imagine you decide to add a new two-story unit to your apartment design. You will add a stair rail to the studio apartment to access that second floor. In doing this, you will practice using 3D Faces and filters. You’ll start by doing some setup, so you can work on a copy of the Unit file and keep the old Unit plan for future reference.

  1. Save the Unit file, and then use File > Save As to create a drawing called UnItloft from the current file. (You can also use the Unitloft.dwg file supplied on the companion CD-ROM.)
  2. Choose Format > Thickness and set the Thickness to 0.
  3. Set the current layer to Wall.

Now you are ready to layout your stair rail.

  1. Click the Line tool on the Draw toolbar. .
  2. At the Specify’ first Point: prompt, Shift+click the right mouse button to bring up the Osnap menu; then pick Point Filters xy.As an alternative, you may enter x y instead of using the Osnap menu. By doing this, you are telling AutoCAD that you are going to first specify the x-coordinate and y-coordinate for this beginning point, and then later indicate the z-coordinate.
  3. At the Specify first Point x y of: prompt, pick a point that is 2′-7″ (79cm for metric users) from the comer of the bathroom near coordinate 25′-6″,25′-5″.(Metric users use the coordinate 777,775.) This will be the first line at the bottom of the stair rail. (You don’t need to be too exact because we are just practicing.)
  4. At the (need Z): prompt, enter 9. (the z-coordinate). Metric users enter 274.
  5. At the Specify next point or [Undo]: prompt, pick x y again from the Osnap menu, or enter xy.
  6. Enter @12<270 Metric users enter @365<270. This locates the x-coordinate and y-coordinate for the other end of the stair rail.
  7. At the (need Z): prompt, enter 0.
  8. Press button to end the Line command. Your drawing should look like Figure 15.20.
    FIGURE 15.20

    FIGURE 15.20


Now you will copy the line vertically to draw the top of the stair rail.

  1. Click the Copy Object button on the Modify toolbar.
  2. Select the 3D line you just drew, and press button.
  3. At the Specify base point or displacement, or [Multiple]: prompt, pick any point on the screen.
  4. At the prompt
    Specify second point of displacement or <use first point as
    enter x y and then [email protected] This tells AutoCAD that your second point will maintain the x-coordinate and y-coordinate of the first point.
  5. At the (need Z) prompt, enter 3’6″-1 to place the copy 3′-6″ on the z-axis, Metric users should enter 106-1 to place the copy 106cm on the z-axis, A copy of the 3D line appears 3′-6″ (106cm) above the original.

In step 4 you specified that the second point used the same x-coordinate and y-coordinate of the base point, so you only needed to enter the z value for the second point-In the earlier exercise, you used a relative coordinate to move door headers to a position 7 higher than their original location. You could have used the same method here to copy the line vertically, but in this exercise you got a
chance to see how the point filter works .

Creating Irregular 3D Surfaces

Sometimes you will want to draw a solid surface so that when you remove hidden lines, objects will appear as surfaces rather than wireframes. If you were to continue drawing the side of the stair rail using lines, the side of the stair rail would appear transparent. So the next step is to fill in the side using 3D Faces.

Loading the Surfaces Toolbar

The 3DFace command and AutoCAD’s 3D shapes are located in the Surfaces toolbar. Right-click any toolbar, then click Surfaces in the popup menu:

Adding a 3D Face

Now that you’ve opened the Surfaces toolbar, you can begin to draw 3D Faces.

  1. Zoom in to the two lines you just created, so you have a view similar to Figure 15.21.
    FIGURE 15.21

    FIGURE 15.21


  2. Click the 3D Face button on the Surfaces toolbar, or type 3f. You can also choose Draw > Surfaces > 3D Face.
  3. At the Specify first point or [Invisible]: prompt, use the Osnap overrides to pick the first of the four endpoints of the 3D lines you drew. Be sure the Ortho mode is off.
  4. As you continue to pick the endpoints, you are prompted for the second,third, and fourth points.
  5. When the Specify third point or [Invisible] <exit>: prompt appears again, press button to end the 3D Face command. A 3D Face appears between the two 3D lines. It is difficult to tell if they are actually there until you use the Hide command, but you should see vertical lines connecting the endpoints of the 3D lines.These vertical lines are the edges of the 3D Face (see Figure 15.22).
    FIGURE 15.22

    FIGURE 15.22


  6. Copy. the 3D face you just drew 5 horizontally in the Q-angle direction.
  7. Use the 3DFace command to put a surface on the top and front side of the rail, as demonstrated in the top and middle images .
  8. Use the Intersection Osnap override to snap to the comers of the 3D Faces.
  9. Now you can save the Unit 10ft. dwg file.

Hiding Unwanted Surface Edges

When using the 3DFace command, you are limited to drawing surfaces with four sides. You can, however, create more complex shapes by simply joining several 3D Faces. Figure 15.24 shows an odd shape constructed of three joined 3D Faces. Unfortunately, you are left with extra lines that cross the surface as shown in the top image of Figure 15.24;but you can hide those lines by using the Invisible option under the 3D Face command, in conjunction with the Splframe variable.

FIGURE 15.22

FIGURE 15.22

To make an edge of a 3D Face invisible, start the 3DFace command as usual. While selecting points, just before you pick the first point of the edge to be hidden, enter 1..J as shown in the bottom image of Figure 15.24. When you are drawing two 3D Faces sequentially, only one edge needs to be invisible to hide their joining edge.

You can make invisible edges visible for editing by setting the Splframe system variable to 1. Setting Splframe to 0 causes AutoCAD to hide the invisible edges. Bear in mind that the Splframe system variable can be useful in both 3D and 20 drawings.

Using Predefined 3D Surface Shapes

You may have noticed that the Surfaces toolbar offers several 3D surface objects, such as cones, spheres, and torus (donut-shaped). All are made up of 3D Faces. To use them, click the appropriate button on the Surfaces toolbar. When you select an object, AutoCAD prompts you for the points and dimensions that define that
3D object; then AutoCAD draws the object. This provides quick access to shapes that would otherwise take substantial time to create.

Turning a 3D View into a 2D AutoCAD Drawing

There are many architectural firms that use AutoCAD 3D models to study their designs. Once a specific part of a design is modeled and approved, they convert the model into 2D elevations, ready to plug into their elevation drawing.

At the end of Chapter 11, you learned about a method you can use to convert a 3D model into a 2D AutoCAD drawing. If you need more accuracy in the conversion, configure the AutoCAD Plotter for an AD! Plotter. Set it up to plot a .dxb file. Your plots then generate .dxb files, which you can import using the Insert > Drawing Exchange Binary option in the menu bar. This opens the Select DXBFile dialog box from which you can select the appropriate .dxb file.

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