800 Part IV Drawing in Three Dimensions

Figure 24-45: The shelled box.

Listing Solid Properties

The MASSPROP command provides information about regions and solids that is useful for engineering applications. The bounding box, for example, is an imaginary box that contains the solid. The calculations are based on the relationship of the solid to the UCS. If you rotate the solid or change the UCS, you get different results. For example, after running MASSPROP to find the center of gravity (centroid) and axes of your model, move the UCS to the centroid and then run MASSPROP again to identify the moments of inertia.

For 2D regions, the area moment of inertia that MASSPROP generates can be used to calculate bending and twisting stresses. You could generate a 2D region of a solid model using the SECTION command and then use the UCS command with the OBJECT option to set the UCS coplanar to the region. The MASSPROP command would then report the area moment of inertia.

AutoCAD assumes a density of 1 for all solids. You can then apply material density multipliers on the values that get reported. Figure 24-46 shows the results of MASSPROP on a solid.

To list a solid’s properties, choose Tools Inquiry Region/Mass Properties. Select the object that you want to list. AutoCAD opens the Text Window to display the calculations. At the Write analysis to a file? [Yes/No] <N>: prompt, press Enter to accept the No default, or rightclick and choose Yes. AutoCAD prompts you for a file name and copies the data to that file.

Figure 24-46: The results of the MASSPROP command.

Summary

In this chapter, you learned how to create and edit solids. You read about:

Drawing standard shapes

Creating extruded and revolved solids from 2D profiles

Using UNION, SUBTRACT, and INTERSECT to create more-complex shapes

Using the INTERFERE command to see the volume of interference between solids

Utilizing the SECTION and SLICE commands to help visualize solids

Using the special 3D editing commands MIRROR3D, 3DARRAY, and ROTATE3D

Using the TRIM, EXTEND, FILLET, and CHAMFER commands for 3D editing

Exploding into surfaces and surfaces into 2D objects

Using the SOLIDEDIT command to edit faces, edges, and bodies — solids as a whole

Calculating a number of engineering functions on solids by using the MASSPROP command

In the next chapter, I cover rendering 3D models.

804 Part IV Drawing in Three Dimensions

Learning the steps

Rendering is a multi-step process. It generally requires a good deal of trial and error to get the exact results that you want. Here are the steps to render a drawing:

1.Start with trial rendering using the default settings. The results let you know what settings need to be changed.

2.Create lights. AutoCAD has four types of lights: ambient, distant, point, and spotlight. I explain lights in the “Creating Lights” section later in this chapter.

3.Create scenes. Scenes are views with lights. You can find out more about scenes in the “Creating Scenes” section later in this chapter.

4.Load materials from the materials library. You can create your own materials. Materials are surface characteristics and include color and/or pattern, ambient light, reflection, roughness, transparency, refraction, and bump map. These characteristics are explained later in this chapter in the “Working with Materials” section.

5.Attach materials to the objects in your drawing. You can attach materials by object, color, or layer.

6.Add a background or fog effect. I discuss these effects in the “Using Backgrounds” section later in this chapter.

7.Set your rendering preferences, if desired.

8.Render the drawing.

The order of the steps is flexible. For example, you can create scenes after you’ve attached materials. Also, after you render, you’ll probably see some room for improvement, so you may go back and change the lights, scenes, and/or materials.

Doing a default rendering

Doing a default rendering often helps you to decide what materials and lights you need to create your final rendering. It also reveals any problems with the models themselves. When you render, you should open the Render toolbar, which contains most of the tools you need. To do this, right-click any toolbar and choose Render.

To render a drawing using the default settings, choose Render from the Render toolbar to open the Render dialog box, shown in Figure 25-2.

I cover the Render dialog box later in the chapter, but there are a couple of things that you can do when you want to get a quick rendering.

Chapter 25 Rendering in 3D 805

Figure 25-2: The Render dialog box.

You can save time by rendering only some of the objects in the view. To do this, use the Rendering Procedure section of the dialog box.

STEPS: Creating a Default Rendering

1.Open ab25-a.dwg from the CD-ROM.

2.Save the file as ab25-01.dwg in your AutoCAD Bible folder. If the Render toolbar is not displayed, right-click any toolbar and choose Render.