4
REVOLVING A 2D SKETCH INTO A 3D OBJECT

The most direct way to produce parametric 3D objects is through manipulating 2D sketches. In the last chapter, you produced a cube by extruding a square. In this chapter, you’ll learn how to use the Revolve feature to produce a spherical object from a sketch, then practice tying features together by smoothing them out with fillets and chamfers.

Creating a Sphere as a Revolve Feature

In this section, you’ll use the Revolve tool to create a solid body by spinning a profile around a central axis.

Sketching the Circle

Start by creating a sketch on the Front plane; remember to click Front on the view cube to orient the view toward the correct plane. All revolves require a central axis—an imaginary line around which the sketched geometry is revolved—in order to create a solid. In this case, that central axis will be the existing y-axis.

Draw a Center Diameter Circle with its centerpoint on the origin and a diameter of 50 mm. Then draw a line from the top of the circle to the bottom. Make sure the line is vertical; if it is, your cursor should automatically snap onto the circle. Your sketch should look like Figure 4-1.

Figure 4-1: A Center Diameter Circle centered on the origin with a diameter of 50 mm

Notice that the line you just drew is blue, which indicates that it isn’t completely constrained. To make sure the line passes through the center of the circle, select both the line and the centerpoint of the circle by holding down CTRL on Windows or COMMAND on Mac. Then, from the Sketch Palette on the right-hand side of the Fusion 360 window, scroll down to Constraints and click Coincident, as shown in Figure 4-2. A coincident constraint forces your selections to align. The coincident should lock the centerpoint onto the path of the line segment, though it can still move anywhere on that path.

Figure 4-2: Adding a coincident constraint will fully constrain the circle sketch.

The selected profile shouldn’t cross the axis of revolution (the y-axis here) but it can touch the axis. Right now, the circle is crossing the axis of revolution, so you need to trim it. You can either select half the circle in the feature options or select the Trim tool and click somewhere on the left side of the circle.

The part of the circle you’re removing should be highlighted in red. The Trim tool cuts the line off at its nearest intersection points. In this case, the nearest intersection points are where the vertical line meets the circle. You should be left with a half-circle that touches the axis of revolution.

Revolving the Circle

Now you can select the Revolve tool. Choose the Profile and then choose the axis of revolution. In order to make sure you successfully selected the y-axis, click the arrow next to the Origin button at the top left of the screen. The arrow should reveal the default reference geometry (shown in Figure 4-3), which includes the automatically generated origin, axes, and planes. You can select Y from there.

Figure 4-3: Selecting the y-axis manually

The Type setting should be either Angle at 360 degrees or Full; for the Operation setting, select New Body. You now have a shiny new sphere like the one shown in Figure 4-4!

Figure 4-4: A basic sphere

Modifying the Sphere

Now that you have a basic sphere, spice it up by adding a couple of features. First, use Extrude to put a hole through the center of the sphere, down its vertical axis.

Because this is a sphere and doesn’t have a flat face, instead of sketching on a model face, you need to sketch on the existing Top plane—that is, the x-z plane, which is created by default. Create a new sketch and then choose the x-z plane from the Origin folder on the left-hand side of the window (shown in Figure 4-5). Then draw a circle centered on the origin with a diameter of 15 mm and execute a cut extrude, choosing a value of All for the Extent option. Select Two Sides for the Direction so it will cut all the way through the sphere.

Figure 4-5: Extruding a 15 mm hole through the sphere’s vertical axis

You should now have an object that looks like a bead; the edge looks a little rough, though, so go ahead and add a chamfer feature to both openings of the hole. You’ll find the Chamfer tool under the Modify menu. It’s used to blunt a selected edge.

You define a chamfer by specifying the distance of the cut from the selected edge—either two different distances, two equal distances, or a distance and an angle. In this case, use two equal distances. Enter a distance of 2 mm and finish the feature so that your model looks like Figure 4-6.

Figure 4-6: The hole now has fancy chamfered edges.

Now you should understand the importance of reference geometry. Next, you’ll finally model something useful!

Modeling a Decorative Pencil Holder

The craft of 3D CAD modeling is most exciting when you’re designing items you can actually use. Maybe you’re planning on 3D printing your models, or CNC milling them, or even sending them out for manufacturing.

In this section, you’ll learn to model a basic decorative pencil holder. You’ll be using the features you’ve already learned about, along with a couple of new ones, like Arc and Shell. If you’d like, you could 3D print this model when you’re done and put something on your desk that makes your co-workers envious of your new skills.

Creating a Simple Box Feature

Begin by sketching a 75 mm × 75 mm square on the Top plane (x-z plane). Using the Center Rectangle option, center the square on the origin. Then extrude the profile you’ve created—100 mm up—to create your base feature, as shown in Figure 4-7.

Next, you’ll create a Revolve feature.

Figure 4-7: The base feature is a 75 mm × 75 mm × 100 mm extrude.

Sketching an Arc

To create a Revolve feature on the Front plane (x-y plane), first draw a sketch that looks like the one shown in Figure 4-8. Constrain the arc so that it’s tangent to a line that’s at an 80-degree angle coming from the bottom. Be sure to use the existing y-axis as the axis for the Revolve tool.

Figure 4-8: Draw the sketch as shown, paying special attention to the constraints.

The only new tool you need to use is the Arc. Draw the arc from the angled line to the top horizontal line; then select the angled line and the arc and give them a tangent constraint from the Sketch Palette. You can use the 3-Point Arc, or you can use the Tangent Arc to save yourself the second step of adding the tangent constraint manually.

Revolving the Arc Feature

With the sketch finished, you can now create the Revolve feature. You do this the same way you’ve done before—by selecting the sketch you just drew as the profile and making the y-axis the axis of revolution. This time, however, change the Operation type to Intersect, as shown in Figure 4-9.

Figure 4-9: Using the Revolve feature with the Intersect option.

The Intersect type leaves behind only the geometry where the existing solid and new solid overlap each other. In this case, the solid that the Revolve feature would have created doesn’t quite reach the corners of the box that the Extrude feature created, so the Intersect operation removes that part of the model—the corners where there is no overlap. You should now be left with a solid that looks like Figure 4-10.

Figure 4-10: The result of the intersection of the Extrude and Revolve features

You now have an interesting shape, but those edges don’t really mesh together well—visually, it’s just a bit jarring. Chamfers and fillets are useful for smoothing out abrupt edges like that, and they give your model a more refined aesthetic. To improve the appearance, add 5 mm chamfers or fillets to the bottom edge as well as to each of the four teardrop-shaped edges, as shown in Figure 4-11.

Your pencil holder should now have round edges.

Figure 4-11: Chamfers and fillets are great for improving the finish of a model.

Hollowing Out the Model with the Shell Feature

Finally, add a Shell feature to hollow out the model; that way, you can actually put pencils inside it.

Choose Shell from the Modify drop-down, make sure Tangent Chain is unchecked, and select the top face. This tells Fusion 360 that this is the face you want to be open. The Direction setting should be set to Inside, and the Inside Thickness setting, which is the thickness of the walls, should be 5 mm.

Click OK, and you’re done! Your model should have an open top and a hollow interior, with 5-mm-thick walls all around. Play around with the Extrude, Revolve, and Chamfer features to tweak the design to your liking.

Printing the Model

If you’d like to 3D print your design, choose 3D Print from the Make drop-down menu. For the Selection option, choose the solid body of the model you want to print by clicking on your model. You can set the quality of the mesh with the Refinement option, which determines how many triangles are used to form the mesh. Usually, the only reason not to use the highest settings is to keep the file size small. Uncheck Send to 3D Print Utility if you just want to save the STL file to print later. Leave it checked to automatically export the STL file to the slicing software of your choice.

Exercises

You should complete the following projects to practice the skills you’ve learned so far. The tools and features covered up to this point in the book will be enough for you to do each of the projects.

Remember, there is no right or wrong way to model something—even though there are best practices. The steps you take to create these may not be the same steps someone else takes; what matters is the final result and that you understand what you did and why you did it.

The actual dimensions of these models aren’t important. They’re just jumping-off points for you to practice and test what you’ve learned. Feel free to alter the designs or add to them as you see fit!

Money Clip

Try modeling the simple money clip shown in Figure 4-12; then try adjusting the design to personalize it or to make it more functional.

Figure 4-12: A simple clip for holding your money!

Shirt Button

Shirt buttons pop off so easily, and who can ever remember where they put those extra buttons that come with shirts? Now you can 3D print your own replacement buttons! The model in Figure 4-13 has a concave top face for a little extra difficulty.

Figure 4-13: A replacement shirt button

Once you’ve mastered this button, try replicating the buttons on a shirt you already own.

Electronics Leg Bender

Do you ever work on electronics projects and find yourself struggling to bend the legs of components to nice, consistent lengths? The handy tool shown in Figure 4-14 can fix that. It has slots to hold components like resistors or LEDs so you can bend their legs to your desired length. Try customizing it to match the spacing on your perfboard.

Figure 4-14: Use this tool to bend the legs of electronics components.

Summary

In this chapter, you developed some important new skills and expanded your modeling vocabulary to include more tools. Throughout the rest of this book, you’ll learn about increasingly more advanced tools and techniques, but you can already complete a lot of projects using just what you’ve learned so far.

The vast majority of the models you make will be composed of features like these, which seem simple at first glance but are so versatile that you can use them to create an incredible variety of geometry. Try the following exercises to model some useful parts; then experiment with using your new skills in a modeling project of your own.