AutoCAD Tutorials: Introducing Layout Features in 2D

Understanding the Modeling Tools

Mainly, there are two principal methods utilized in generating 3d models in AutoCAD but they will be discussed later in more detail in the next chapter as I did mention earlier; Those are Surface modeling and Solid modeling.

Anyway, if we had to define each one of those two methods, we have to note the following: 

• Surface modeling uses multiple faces connected to create geometric forms and models; for instance, a simple cube has to be created with six squares of faces connected via their edges. Likely, a pyramid is a composition of four triangular faces attached to the four edges of a square-shaped face which is its base.

• Solid modeling on the other side, adopts an easier method to create models, and it offers many advantages, especially in mechanical designs and engineering: It is a way of defining 3D objects as solid forms rather than wireframes with surfaces linked together.

When you are creating a 3D model using solid modeling you start with the basic forms of your model like cubes, cylinders, or cones, for example. Those basic solids are called primitives. Then using more of these, you can start to add to or subtract from your basic forms. (Fig.1)

Fig.1- The solid primitives, Photo-source: flylib.com

For example, to create the model of a tube, you first create two solid cylinders, one with a smaller diameter than the other, and move them so they’ll have their centers aligned. And then if we subtract the smaller one from the largest one we will obtain a tube-shaped model. (See Fig.2)

Fig. 2- Creating a tube using solid modeling, Photo-source: flylib.com

Similarly, we can create an endless of geometrical forms and shapes by simply deducting and adding them from each other.

How to Create Solid Forms?

As we noted earlier, we will use the solid modeling method to create a simple model that we will need to demonstrate in the next exercise on using the layout in our presentations.

Congratulations! You did by now draw your first primitive, a box equal to (7 wide x 9 length x 2 height) units. (Fig.5)

Fig.5- The first primitive box is completed.

Now let’s try to change the view taken for the model so you can see the scene more clearly from another angle; You can do this via several methods, among them is by typing "_View" in the command line which initiates the View Manager dialogue box that provides a list of Presets Views, featured with orthogonal and isometric views, but mainly the isometrics views, based on the orthographic WCS (World Coordinates System) of the ACAD drafting system. (Fig.6)

Fig.6- The View Manager dialog box

For instance, selecting the preset SW isometric view will give us an orthographic view from the SW corner defined by the following convention:

Another useful conversion of the UCS accredited by AutoCAD is to convert the X and Y-axis into their geographical alternatives, i.e. the North, West, South, and East direction that could replace the x and y axes as follows:

• The North direction represents the positive portion of the Y-axis,
• The South direction symbolizes the negative Y-axis,
• The West direction is the negative X-axis,
• And finally, the East direction is the positive portion of the X-axis. (Fig.7)

Fig.7- A schematic view showing an approach for the Preset Views

Likely, you can employ the ViewCube in the top-right corner of the drawing area, to generate the same preset views previously cited. (Fig.8)

Fig.8- The Preset Isometric Views dialog box: SW, SE, NE, and NW Isometrics

Fig.8- The Preset Isometric Views dialog box: SW, SE, NE, and NW Isometrics

How to Convert a Closed 2D Polyline into a 3D Solid?

Here we can proceed with the exercise in two different ways although they both lead to an identical result. The first method consists of simply drawing the second solid wherever you want in the model space and then moving it to its appropriate final location.

But another method involves changing the position of the UCS to be able to model in place, without the need of moving the model later to its correct place.

Now let’s add another geometric solid element, such as an L-shaped form with the second method, which consists of changing the UCS origin to the top of the first drawn element. To do so, we will simply type UCS in the command line and press Enter. At the next prompt Specify origin of UCS or [Face/NAmed/OBject/Previous/View/World/X/Y/Z/ZAxis] <World>: we will pick on the desired new point which is the coordinate (0,0,+2).

Name the newly created UCS when prompted as new_UCS. Also, you have just defined the new working plan* for creating your new solid element.

In other terms, we have changed the Z-axis value of the WCS initially positioned at (0,0,0) to the new position with a positive Z-coordinate value equal to +2. This means a new UCS Origin inherited from (0,0,0) to (0,0,+2) as shown in Figure 9.

Fig.9- The new UCS position at the top of the box, and exactly positioned over the origin at the new coordinates (0,0,+2)

This time we’ll create a new solid generated from a polyline. How is that? Let’s keep practicing…
 
1. Click the Polyline tool from the Draw Panel. You can also type PL in the Command-Prompt box for a similar process.

2. At the Specify start point: prompt, start your polyline from the point with the coordinates (+7,+9) which replaced the point (+7,+9,+2) as the current UCS is now new_UCS, defined earlier.

3. Then complete the remaining shape shown in Figure 10, and close the Polyline command when prompted to do so, by typing Close or just C, at the prompt Specify next point or [Arc/Close/Halfwidth/Length/Undo/Width]:

So far, you have drawn two primitives’ boxes by using the Box and the Extrude commands.

Just for variation, this exercise had you create the second form by converting a polyline into a solid, but you could just as easily have used the Box option for that as well. Note that the Extrude option can convert closed polylines, 2d faces, regions, and circles into solids. While 2d and 3d polylines and regular lines can be converted into surface meshes, 3D Faces, and 3D polylines cannot be extruded into solids.

Other Primitives Options

Before continuing, let’s explore the options for primitives that we haven’t had a chance to use yet.

• The Cone draws a circular cone with a circular base; Drawing a circular cone is much like drawing a circle, with an additional prompt asking for a height.
• The Sphere acts like the Circle command, but instead of drawing a circle, it draws a sphere.
• The Torus creates a (donut-shaped solid). You are prompted for two diameters or radii, one for the diameter or radius of the torus and another for the diameter or radius of the tube of the torus.

• Wedge creates a wedge-shaped solid; This command acts much like the Box command we used before. You have the choice of defining the wedge by two corners or by its center and corner. Note that the wedge side is z-axis direction sensitive; it is defined according to the rotation of the z-axis. Now, know the basics, practice more to learn how it acts and to manipulate it!

In the next post, we will be creating and combining solid primitives. The commands needed to create such complex solids are available on the Edit Panel from the 3D Basics Workspace. (Fig.12)

Fig.12- The Edit Panel from the 3D Basics Workspace list

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