After a long break this summer, I’m excited to continue my AutoCAD 3D Conceptual Design series. I hope you’ve had the chance to follow along as I step through the process of designing an air hockey paddle. Keep in mind that these postings aren’t so much about creating the air hockey paddle as they are about learning the variety of tools and techniques that enable you to take your ideas from concept to completion all within the familiar AutoCAD design environment. You can apply the ideas you learn from these postings to any 3D conceptual designs in any industry.
To refresh your memory (and mine) about what I already covered, here are links to the previous postings:
AutoCAD 3D Conceptual Design 101
AutoCAD 3D Conceptual Design 102
AutoCAD 3D Conceptual Design 103
AutoCAD 3D Conceptual Design 104
AutoCAD 3D Conceptual Design 105
AutoCAD 3D Conceptual Design 106
AutoCAD 3D Conceptual Design 107
AutoCAD 3D Conceptual Design 108
AutoCAD 3D Conceptual Design 109
AutoCAD 3D Conceptual Design 110
AutoCAD 3D Conceptual Design 111
In the previous postings, I created all of the basic primitive objects to create the air hockey paddle. Most of the primitive objects, such as the sphere and cylinders, represent material (mass) that I want to add to the paddle. The cone primitive, however, represents material that I want to remove from the paddle.
To add and remove solid objects, you can use Boolean tools. You’ll find these tools on the Home tab of the ribbon when the 3D Modeling workspace is active.
The Union tool joins the selected solid objects into a single composite solid object. The Subtract tool removes selected objects from other selected objects; also forming a composite solid. The order in which you perform a combination of Union and Subtract operations can create different results. For example, if I union the cylinders and sphere for the air hockey paddle and then subtract the cone, I get a big gap between the upper part of the model (the handle) and the lower part of the model (the striker). This is still a single composite solid but it looks like two separate objects, which isn’t the result I’m looking for.
The solution is easy. It’s just a matter of changing the order of my Boolean operations and the objects that I select. I can use UNDO (just as you would expect) to return to a previous state where each of the primitives are separate objects.
When using the Subtract tool, it’s important to read the command prompts to ensure you are selecting objects in the appropriate order. You must first select the objects you want to subtract from and then select the objects you want to subtract from them. For example, if I want to subtract one of these cylinders from the other, the results vary depending if I first pick the cylinder on the left or the cylinder on the right.
In this example I only selected on object to subtract from and one object to subtract from it. You can, however, select more than one object to subtract from or to subtract from them. For example, I could select box and the cylinder (below) as the objects to subtract from then select the sphere and the cone as the objects to subtract from them. The result is shown.
Since you can select multiple objects, you must remember to press enter to finish the “select from” option before you select the object(s) you want to subtract from them. This may seem obvious but, speaking from experience, it’s easy to make a mistake with the selections if you’re new to the Subtract tool or if you haven’t used it for a while because this is one of the few AutoCAD commands that prompts for two selection sets.
Okay, back to the air hockey paddle… I’ll use the Subtract tool to first subtract the cone from the lower cylinder and then I’ll union the newly created composite solid with the remaining cylinder and sphere. This is the result I was looking for!
- The Union tool combines selected solids to create a composite solid.
- The Subtract tool removes solids from selected solids to create a composite solid. It requires two selection sets: Objects to subtract from and Objects to subtract from them.