ewhite: May 2008

This is a tutorial from the sketch up help centre that i used to create a dome.

How do I draw a bowl (or a dome)?

Here's one way to draw a bowl. You'll draw a circle on the ground plane and the outline of a bowl directly above it. Then you'll use the Follow Me tool to turn the outline into a bowl by having it follow the original circle on the ground plane.

Use the Circle tool to draw a circle on the ground plane. The first time you do this, you'll find it easiest if you start your circle at the origin point (the point where the red, green, and blue axes intersect). Then, with the Circle tool still selected, hover way out on the edge of the drawing until the circle cursor turns red or green, and then press and hold the Shift key to lock that inference direction (both of these inference directions are perpendicular to the ground plane)
With the inference direction locked, pause over the center point of the circle for a couple seconds, and then move straight up and click to set the center point of a circle that is perpendicular to the original circle.

Why pause over the center point of the first circle? When you are drawing in 3D, it's easy to draw something that looks like it's located exactly at a point relative to another object. But if you rotate around, sometimes you'll find that the new object is located somewhere entirely different in 3D space from where you thought it was. To avoid this, you can use SketchUp inferences. Pausing over the center point of the original circle activates a temporary inference that helps guide your move straight up from that point. This enables you to begin the new, perpendicular circle directly above the center point of the original one.
Using the Offset tool, point at the outer edge of the circle, and then click and drag in an offset circle. This will end up being the thickness of the bowl.
Do this next step carefully. Draw a line across the outer circle where you want the top of the bowl to be. Then draw a second line on top of the first, but just across the inner circle. You may need to zoom in close in order to start and end the line at the exact points where the first line crosses the inner circle.

Why do you have to redraw the inner part of the line? When you draw a circle using the Circle tool (or a curve using the Arc tool, or a curved line using the Freehand tool), you are actually drawing a special type of multiple-segment line called acontinuously joined line. These types of lines are special because SketchUp joins the endpoints of the segments together in a way that makes the entire line act like a single, continuous entity; if you click a continuously joined line with the Select tool, you'll see that the entire line is highlighted. (Compare this to a multiple-segment line you create with the Line tool; if you click that type of line with the Select tool, only the segment you clicked is highlighted.)

In order to delete a portion of a continuously joined line (which you'll need to do in the next step), you need to break the continuity. To do this, you can use the Line tool to draw a line that begins or ends somewhere on the line you want to break. This creates a real segment endpoint that breaks the line's continuity. When you drew the line that defined the top of the bowl, its beginning and ending endpoints split the outer circle into two continuous lines. But when a line simply crosses another line like the inner circle, it doesn't actually intersect with the line it crosses, so it doesn't break the continuity. Drawing the second line across the inner circle breaks the inner circle into two continuous lines.
Now you can erase all the geometry that isn't a part of the bowl outline. First erase the top of the outer and inner circles.
Next, erase the straight line at the top of the bowl that runs from one side of the inner circle to the other, so that you're left with just the outline of the bowl. Then use the Select tool to click the face of the original horizontal circle below the outline.
Select the Follow Me tool (open the "Tools" menu and click "Follow Me"), and then click the face of the bowl outline. A 3D bowl should result. Soup anyone?
To finish things up you can delete the original horizontal circle