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3D Modeling 3: using UNION and SUBTRACT commands

8 Comments Jul-18-2007 | Posted by Orhan Toker | Printable Version | Level |

AutoCAD 2007 and higher versions

Hello Daily AutoCAD readers,

In this article of series of articles about 3D modeling, I will try to explain about UNION and SUBTRACT commands by an example that uses only a BOX solid. Our goal is to obtain the solid entity that is shown in Fig. 1.

Fig.1

We can start by drawing the box that is at the button. It has dimensions as width 60, depth 40 and height 15.

Fig.2

As I have explained previously, as the view angle that we selected is on the positive direction of X, Y and Z axis, we can easily use dimensions that we would like to give to the drawings.

Now, let’s draw the other box.

Fig.3

Command: _box
Specify first corner or [Center]:
Specify other corner or [Cube/Length]: @60,-15,45

This time, you might have noticed that the starting point of our second box is the upper left corner of the other box. Because, this corner is a definite point in our drawing. As the second point of out new box is prompted then we entered three values. As you may remember from our previous coordinate entry lesson, we are entering relative coordinate entry and we are writing x, y, z values after @ symbol.  Pay attention to entering Y value as -15, because drawing is being made on the opposite direction of Y axis. 

Next, we will draw the small 15×15×15 cube and position it into its locations. You can draw the cube anywhere. Use “Cube” option in BOX command.

Command: _box
Specify first corner or [Center]:
Specify other corner or [Cube/Length]: c
Specify length: 15

Fig.4

After drawing the cube, then carry it to upper middle point as shown in Fig. 4.

Now, it’s time to use UNION and SUBTRACT commands.

Fig.5

UNION command is pretty simple. Use UNION command from DASHBOARD as shown in Fig. 5. This command is very easy to use. It is used to combine two solid entities into one and it prompts you to select the entities to be combined. Now, use the two boxes one of which sits perpendicular to other and press ENTER. You will see that the boxes are merged into one.

Finally, we will subtract the cube from the main body by using SUBTRACT command.  Run the SUBTRACT command, select the main body first and press ENTER. Now, select the cube and press ENTER. You will notice that the cube is subtracted from the body.

Fig.6

As you can see, this is very simple. By this way, we did our first solid 3D model.

See previous articles of series : See “3D Modeling” chapter in AutoCAD Lessons.

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