# Free Tutorial: Circles

Loading...

View Transcript
You can draw lines and polylines now. And now, you're going to need to know how to draw circles. Circles are used for many things. Holes, different designs, wheels, and gears. I could go on. But you get the idea. A circle is very simple. In geometry, it is defined as all of the points that are equally distant from a single point. To draw a circle in AutoCAD, use the circle command. Just type "circle" on the command line, or just the letter C for the command alias, or click on it up here in the Draw panel on the Home tab in the ribbon. By default, you will be asked for the center of the circle as the starting point. Pick one. Anywhere. Then you will be asked for the circle's radius. . Enter in 10 units in this case. Press Enter. Zoom in or out if you need to. There's your circle. Very simple, very easy to do. You may, though, want to create a circle according to its diameter. Start the circle command again. Pick your first point. And now instead of clicking your point again, you can go to the command line and click on the Diameter function or option, or type in the letter D. Remember on the command line, when it gives you additional options, and they're highlighted here, the blue letter at the very beginning, which is typically just the first letter, but will oftentimes include the first two or three, that's all you'll have to type in. You don't have to come down here and click. Just hit D for diameter, press Enter, and now type in 20. We just drew the exact same circle, and just in a different way. That's important to know. Because sometimes, you have the diameter, and sometimes you have the radius. If I have one, I know what the other is. That's true number-wise. But oftentimes when you're drawing an AutoCAD, for example, if I have this line and this line, and I need to draw a circle, what do I have? Do I have a radius, or do I have a diameter? Well, that depends. If I start circle and I draw from this end point, and I want to draw to this end point, I have a radius, not a diameter. That's true. But if I want the circle to come to the middle of these two lines, I will need the diameter. I'll show you the difference. I'm drawing with the radius now. So I will type in end for my endpoint and draw there. That's my circle. Let's start again the circle command. Type E-N-D for endpoint. We're snapping to the endpoint of this line. But now hit D for diameter. Press Enter. As I stretch, I'll type in end again and go to the endpoint of that line. And there you go. I just found the middle point between these two points in drawing a circle. You'll find situations similar to this while you're drafting. You won't always have just the radius. You won't know where the center point is. You won't know where the endpoint is. You'll need to have to draw a circle in a different way. Well, that's good. Because you can. There are other ways to draw circles inside AutoCAD besides using the center and radius, or center and diameter. Those other methods are drawing a circle by three points about the circle. Another one is by drawing two points about the circle. And then the third option that you will have here in this list is drawing at two tangent points and the radius. You say, well, how will I know when to use what? That's great. We'll look at an example. Open up the file that came along with this training video from the fifth project chapter, and go to the Circle Arcs Example file. Click Open. This is a very simple example of some ways to use the different methods of drawing a circle. The three-point option allows you to draw a circle based on three points along the circle. So start your circle command. And instead of picking your center point, click on the 3P option, or type in 3P. So let's say we have these three lines. We don't know where our center is. We don't know where anything is, really. All we know is that we need to come from the middle of this line, the end of this line, and the end of that line. And our circle needs to go about those. So let's pick our first point. Type in mid for midpoint. Press Enter. Look for the green triangle glyph in the midpoint tag. Click. Now type in E-N-D for endpoint. Enter. And click up here. After we get two points, AutoCAD will generate a preview of our circle. It will always pass through the midpoint here, and the endpoint there. We don't know the radius, or the diameter, or the center of the circle. But we do know that we need it to pass through the end point of this line here. Press Enter. And there you go. We drew our circle. Very simple, very easy to do. Let's try it again. Type in 3P. Enter. Pick one point. Pick two points. And now the third point. And there you go. The two-point option works exactly the same way, but with one last point. Let's draw it. Start the circle command. Type in 2P for two points. Press Enter. Now I want to show you a new objects snap. It's called quadrant. Just type in Q-U-A. And this will snap to the quadrant of a circle. That means either the left or rightmost points, or the top and bottommost points. If you look at the center of a circle and draw a plus through it, a line straight up the y-axis and a line straight across the x-axis, these are the points on the circle that you will snap to. Pick here. And now we can have our circle go anywhere. We can draw a lot of different shapes. If you turn on your ortho command, just as we did with the line and polyline, we will draw this circle either across the y or the x-axis. There we go. Press Enter to start the circle command again. And the circle command will always default to the center point radius drawing method. So if you want to do anything else, you have to tell AutoCAD that you want to do it differently. Type in Q-U-A again. And there we go. This is a good start to a snowman. Now let's look at the other option that was available to us. If you start the circle command, you can see we have the 3P, 2P, and the TTR, or the Tangent, Tangent, Radius. Just type in the letter T and follow the instructions on the command line. It's asking us to specify the point on an object for the first tangent of the circle. So let's say we have these two angled lines. We want our circle to be tangent to this line, and tangent to that line. So you will see that the glyph is up here of a tangent line with the three ellipses. That means it will draw it tangential to this line. . And now to this line for our second point. And now we have to give it a radius. Let's give it a radius of five units. Press Enter. And there you go. This circle is tangent, as you can see, to that line here. And it is also tangent to this line. That can be very useful when you're trying to figure out an arc archive for two different ends. You can use the trim command. Just type in T-R. Press Enter. Select everything. Hit Enter again. Click the circle. And then click the line. And then the line. And now, you've created a nicer rounded corner for your object. When you type in a radius or diameter for a circle, you can either type in the value, but you don't always have to do that. You can just pick your point. So keep that in mind. The three parallel lines that we had here were three units apart, but you could pretend you don't know that. Just draw a circle. We're going to erase this one first. Start the circle command. Pick an endpoint. And then for the radius, you could pick the endpoint again. And there you go. I didn't know what that radius was, but they are at 10 units apart. You can draw circles in a lot of different ways with a lot of different methods. Which one you pick will depend on the information you have, and what you're trying to create.