Chapter 24 Creating Solids and Editing in 3D

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On the	3D Kitchen Plus is a library of 3D kitchen cabinets. You can choose from several models.
CD-ROM	Look for it in Software\Chap24\3D Kitchen Plus. Flatten is a program that flattens
	everything except blocks from 3D to 2D.

Sectioning and Slicing Solids

In many mechanical drawings, you need to show a cross-section of your models. A crosssection displays the inside of a 3D object. The SECTION and SLICE commands are both used to create cross-section views of your 3D models.

Using the SECTION command

The SECTION command creates a 2D region from a cross-section of a 3D model along a plane you specify. The original objects are left untouched. Figure 24-20 shows a region created using the SECTION command.

Region created using SECTION

Figure 24-20: The region created using SECTION is shown with a dashed line.

Tip	The SECTION command creates the region on the current layer. Make the current layer color
	different from the object layer color so that the region is clearly visible.

To use the SECTION command, choose Section from the Solids toolbar. Select the object you want to section. AutoCAD displays the Specify first point on Section plane

by [Object/Zaxis/View/XY/YZ/ZX/3points] <3points>: prompt. Use these options to define the plane of the cross-section. Table 24-1 explains how to use the options.

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	Table 24-1: SECTION Options
Option	Description
Object	Enables you to choose a circle, ellipse, arc, spline, or 2D polyline.
Zaxis	Defines the plane by defining a Z axis. The sectioning plane is then the XY plane
	perpendicular to the Z axis you defined. You define the Z axis by first specifying a point
	on the sectioning plane. This point is the 0,0,0 point (for purposes of this command only)
	where the sectioning plane and the Z axis meet. Then you pick a point on the Z axis.
View	Defines the section plane parallel to the current view at the intersection of a point you
	specify.
XY	Defines the section plane parallel to the XY plane at the intersection of a point you specify.
YZ	Defines the section plane parallel to the YZ plane at the intersection of a point you specify.
ZX	Defines the section plane parallel to the ZX plane at the intersection of a point you specify.
3points	This is the default. Specify three points to define the section plane. Using object snaps is
	a good idea.

You can move the region you create and view it separately to spot errors in your models.

Using the SLICE command

The SLICE command slices a solid into two parts along a plane. The original solids are modified but can be reunited with UNION. You can delete either part or keep both. Figure 24-21 shows the result of slicing a model, after one-half of the model has been deleted. This can help to identify problems in the construction of the model. For example, this slice reveals a fault with the model — the flat disk continues through the central tube — not the desired result.

Figure 24-21: The result of slicing a solid and retaining one of the resulting pieces.

To use the SLICE command, choose Slice from the Solids toolbar. Select the object you want to slice. AutoCAD displays the Specify first point on slicing plane by

[Object/Zaxis/View/XY/YZ/ZX/3points] <3points>: prompt. Use these options to define the plane of the cross-section. The options are the same as for the SECTION command and are explained in Table 24-1.

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On the	The drawing used in the following Step-by-Step exercise on slicing solids, ab24-03.dwg, is
CD-ROM	in the Results folder on the CD-ROM.

STEP-BY-STEP: Slicing Solids

1.If you have ab24-03.dwg open from the previous exercise, use it. Do a regen to remove the hidden view. If you don’t have it open, open it from your AutoCAD Bible folder or from the Results folder of the CD-ROM. Make sure that OSNAP is on. Set running object snaps for endpoint, midpoint, center, and quadrant. Make sure you have both the Solids and the Solids Editing toolbars open. The drawing is shown in Figure 24-22.

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3

1

2

Figure 24-22: The 3D model for slicing.

2.Save your drawing as ab24-04.dwg in your AutoCAD Bible folder.

3. Choose Slice from the Solids toolbar. Follow the prompts:

Select objects: Select the solid model.

Select objects: Right-click.

Specify first point on slicing plane by [Object/Zaxis/View/XY/YZ/ ZX/3points]

<3points>: Pick the quadrant at 1 in Figure 24-22.

Specify second point on plane: Pick the quadrant at 2. Specify third point on plane: Pick the quadrant at 3.

Specify a point on desired side of the plane or [keep Both sides]:

Pick the model at 4.

4.As mentioned earlier, the slicing reveals an error — the disk cuts through the central tube, as shown in Figure 24-23. To fix the error now, choose Zoom Realtime from the Standard toolbar and zoom in so the model takes up the entire screen.

5.Start the CIRCLE command. At the Specify center point for circle or [3P/2P/ Ttr (tan tan radius)]: prompt, pick the midpoint at 1 in Figure 24-23. At the

Specify radius of circle or [Diameter]: prompt, pick the endpoint at 2.

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2

Figure 24-23: The solid after slicing and deleting one-half of it.

6.Choose Extrude from the Solids toolbar. Select the new circle. Set the height of extrusion to 16 and accept the default taper angle of 0 (zero).

7.Choose Subtract from the Solids Editing toolbar. At the Select solids and regions to subtract from... Select objects: prompt, select the large solid and rightclick to end object selection. At the Select solids and regions to subtract...

Select objects: prompt, select the new extruded circle you just drew and right-click. AutoCAD subtracts the extruded circle from the larger model.

8.Use the HIDE command to hide the model. Your drawing should look like Figure 24-24.

Figure 24-24: The solid after subtracting the extruded circle and doing a hide.

9.Save your drawing. If you’re continuing on to the next Step-by-Step exercise, keep the drawing open.

Note If you wanted to correct the model, you could subtract out the circle as you just did in the exercise, mirror the entire model, and use UNION to make the two halves whole. Mirroring in 3D is covered in the next section. You could also undo the slice as soon as you saw the error and make the correction on the entire model.