Circles and Lines: Creating 3D Solid Primitives

6 Aug, 2006 By: Lynn Allen

Take your first step into the world of 3D in AutoCAD.

By now you've heard that AutoCAD has made a serious effort to enter the world of 3D. You may be tempted to continue living in your 2D world and let all those cool 3D features linger by the wayside, but what fun is that? You'll find that designing in 3D is much more rewarding than living in a flat world. This month, we'll create 3D objects and continue down this series focused on 3D.

Last month I discussed how to properly set up your 3D environment. If you missed the installment, I recommend you read it now before going forward with this month's tutorial.

One Stop Shop
Open the ACAD3D prototype drawing and display the new Dashboard -- the one stop shop for all things 3D. Display it by choosing the new 3D Modeling Workspace, or by going to Tools / Palettes / Dashboard. I prefer to anchor my Dashboard to the side of the screen because I like as much screen real estate as I can have. To do this, right-click on the Dashboard bar and select Anchor right (or left).

Prepare your user interface before starting to draw in 3D.

Open and close a control panel by selecting the arrows.
The Dashboard is comprised of seven different control panels. The 2D Draw panel is turned off by default, but can easily be displayed by using the Dashboard shortcut menu. You can expand each of the panels to display more commands by clicking on the arrows on the left of each panel as in the figure below. You can have only one panel expanded at a time, consequently when you expand another panel, the previous one rolls up. Unfortunately, the Dashboard is not customizable, so what you see is what you get!

All the Tools
This month, let's focus on the 3D Make panel that contains nearly all the tools you need to create 3D objects. Let's start with the primitives (cone, box, cylinder and the like) as they are the easiest to work with.

The 3D primitive commands feel very much like their 2D equivalent. For example, a cylinder is based on a circle and consequently there are similar options in both. You can select a center, radius, 2P, 3P and TTR as the base of your cylinder, just as you'd find in the Circle command. This makes it so much easier to learn the new 3D commands. As you provide input, you can see the objects as they are created ensuring you get the desired results.

Box. Let's start with the easiest of all -- Box. Here the options are similar to the ones found in the Rectang command. The default way to draw the box is to select the two opposite corners of the base, and then the height. A positive value for the height draws the box up the positive Z axis, a negative value draws the box down the negative Z axis.

  • Command: Box
  • Specify first corner or [Center]: Select a point or enter C for center
  • Specify other corner or [Cube/Length]: Select the other corner of the box or enter an option

The Box command also gives you the option of creating a cube where all the sides are of equal length. If you prefer to indicate precise measurements for the length, width and height, you can use the Length option after you select the starting point of your box.

If you prefer to construct your box by selecting the Center of the box first, that's also an option.

It's easy to use grips to alter your box after the fact. Just select the box to display the grips and tug on the various grips to change the size of the box. The grip located in the center of the base of the box can be used to move the box. We'll get more into editing the 3D objects in a future column.

The new 3D grips make it easy to edit your 3D geometry.

Wedge works similar to Box.

Cones are simple to create by defining the base and the height.
Cone. Draw a cone by defining the circle that defines the base followed by the point of the cone. The options for the base mirror the Circle command as mentioned earlier. The Elliptical option lets you create a cone with an elliptical base.

  • Command: Circle
  • Specify center point of base or [3P/2P/TTR/Elliptical]: Select a point or enter an option
  • Specify base radius or [Diameter] <default>: Specify a base radius by selecting or inputting a value, or enter d to specify a diameter

There are several ways to define the height of a cone. Simply select the top point and indicate with a value or select 2Point to select two new defining points to determine the height.

  • Specify height or [2Point/Axis endpoint/Top radius] <default>: Specify a height by manually selecting a point or by keying in a value, or enter an option
You can also use the Cone command to create a cone frustrum, which means there's a radius for the top of the cone as well (think volcano!).

Creating a top radius in the Cone command creates a cone frustrum.

Cylinder and Sphere follow along in the same footsteps as the Cone command. The Torus command creates your Krispy Kreme donuts and is also based on circular information. You must determine the position and size of the hole and the size of the tube. Even though we think of tubes as being hollow, the Torus command does generate a solid. And I'm sorry, there's no way to create a jelly donut -- inside diameter of 0.

Pyramid is new and is based on the good old Polygon command, consequently you select the number of sides (3 to 32), inscribed/circumscribed and you can indicate a top radius as well creating a pyramid frustrum if needed (sounds like a personality disorder to me).

Give these new solid primitives a try and you'll see how easy it is to get started in the world of AutoCAD 2007 3D. Next month, we'll continue down the 3D road as we explore more options in creating 3D objects.

Until then...Happy AutoCADing!

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