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Creating arcs

From: AutoCAD 2009: 2D Drafting Techniques

Video: Creating arcs

At first glance, the Arc command may seem a little intimidating because of the sheer number of choices available. You see there are at least 11 different ways to construct an arc depending on what information you have. In this session, we are going to look at the many ways we can construct arcs using AutoCAD. Before we get started, let's take a look at my running object snaps. I'm going to come down and right-click on my Object Snap mode and I have my Typical, Center as well as Endpoint object snaps set. Let's hit Escape to clear the menu. To launch the Arc command, I'm going to come up to the Draw panel of my ribbon and I'm going to click the tool right here. Now when we create an arc, it's essentially a three-click process. I'm just going to click three times, one, two, three. I just created an arc on my screen.

Creating arcs

At first glance, the Arc command may seem a little intimidating because of the sheer number of choices available. You see there are at least 11 different ways to construct an arc depending on what information you have. In this session, we are going to look at the many ways we can construct arcs using AutoCAD. Before we get started, let's take a look at my running object snaps. I'm going to come down and right-click on my Object Snap mode and I have my Typical, Center as well as Endpoint object snaps set. Let's hit Escape to clear the menu. To launch the Arc command, I'm going to come up to the Draw panel of my ribbon and I'm going to click the tool right here. Now when we create an arc, it's essentially a three-click process. I'm just going to click three times, one, two, three. I just created an arc on my screen.

Let's create one more. This time when we create the arc, we are going to keep a closer eye on our command line. Let me launch the tool again. AutoCAD is asking for my start point and notice at the command line I could also specify a center at this point. I'm going to pick on the screen. Now that I have set my first location, I could specify a second point as well as the center or the endpoint of my arc. Once again we'll click and then I can pick a point on screen to finish my arc. Now, why did I say arc seem a little intimidating? Well, I'm going to come up and click the flyout next to the Arc tool.

Notice there are 11 different ways to create arcs in AutoCAD depending on what information you have. Now, it's important to know that there is only one Arc command. The default happens to be the 3-Point arc. Each one of these other options is merely a shortcut to the various sub-options that are available within the command. Every one of these methods could be accessed by selecting 3-Point and then just choosing the options from the command line. Let's hit Escape to clear this menu and I'm going to erase these arcs. I would like to take a second to talk about the pieces of information that we can use to construct an arc.

Now as we go through these components, always remember that an arc is nothing more than an incomplete circle. Let's not over-complicate the issue. In most cases if you have difficulty creating an arc, simply create a circle and trim it. One component we can use to create an arc is the start point. Another component we can use is the arc's endpoint. We can use the center point as well. Another piece of information that is helpful is the radius. The radius is the distance from the center point to the end point of our arc. We can use the included angle to construct our arc. Now, an included angle is the angle drawn from the endpoint to the center point to another endpoint of our arc.

The included angle is sometimes called the delta angle of your arc and looking at my example on screen, I can see this arc has an approximate included angle of 90 degrees. We can use a point on the arc as one of our components. We can also use the chord length. The chord length is the straight-line distance from the start point to the endpoint of our arc. Finally, we can also use the start direction. At what angle does my arc exit my start point. This is also called our direction of tangency. In the example on screen, the start direction would be 90 degrees because I'm coming out of my start point straight up. When constructing an arc in AutoCAD, I can use any three pieces of information that we see on the screen. Let's return to AutoCAD and we'll take a look at the tool.

Now, we're not going to be going through every method of creating an arc in this lesson. We're going to look at several of them. If you look at my screen, you can see I have created some rectangles. What we're going to do is use these rectangles to sketch out some decorative window concepts. I am going to zoom in on one of these. Now this geometry was created using architectural measurements. Let's create our first arc. Let's say I would like to create an arc that starts right here and then curves up and ends when it hits this vertical line. Well, I know the start point of my arc, I know the center point of my arc and I know the endpoint of my arc must fall on this line. Let's go up to our Arc flyout and click. I'm going to select the Start, Center, End option.

I will click my start point, I'll click my center point and notice as I pull away, I'm creating a rubber band effect and I just need to click my last point to finish my arc. One thing I want to mention, AutoCAD wants to create our arcs counterclockwise. You would think if I was to pull down, my arc would be drawn the other direction. It's not, okay? Keep that in mind when you are constructing arcs. Let's me click my last point. I'm going to come up and grab the endpoint of this line. Let's create the arc on the other side. Once again I'm going to launch the Start, Center, End tool. I'll click my start point, I'll click my center point and notice that AutoCAD wants to draw this counterclockwise, unfortunately that's not going to work for me in this case.

Now, I don't have to pick another selection from the flyout. Remember those selections are merely shortcuts to the sub-options of the command. I'm going to finish this arc by using the command line. If we take a look right down here, we can see that I can enter an angle or a chord length at this point. I'm going to right-click and select Angle because I know this angle must be 90 degrees. Now, in this case, I want the arc to go clockwise, so I'm going to type -90 and hit Enter. Let's finish this window by creating a rounded top. I would like to create an arc that starts from this endpoint that sweeps up through the mid-point at the top and then ends at this endpoint. Let's click the Arc flyout. I'm going to select the 3-Point option and we'll create an arc from this endpoint to the Shift+Right-click midpoint of this line to the endpoint of this arc.

Let's pan this over. I have got another example. In this case, let's say I would like to create a single arc that starts here and spans all the way up and comes down and ends on this side. Once again I'm going to click the Arc flyout. We're going to try the Start, End Angle method because I know my start point is here, my end point is here and my angle is going to be 180 degrees because it's half of a circle. Let's back up just a little bit and we'll look at our last example. In this case, I would like to create more of a Gothic style window. So I'm going to stretch this middle rectangle a little bit taller. Let me launch my Stretch command, we'll do a crossing window around this geometry. I'll right-click and then I'll pick my corner and we'll pull straight up. Let's lock our Ortho.

We'll pull up and we'll type 1 foot, Enter. Now, in this case, I know my start point of my arc, I know the end point of my arc, I also know the arc direction. So I'm going to click my flyout. I'm going to come down and select Start, End direction. My arc is going to start here. We are going to draw it to the Shift+Right -click, midpoint of the top and I know the arc direction happens to be 90 degrees. That was if I pull to the right, I can also select 0 or I can pick 180. Let's pull up and we'll pick a point on screen. Let's create one more arc to finish this up. I'm going to launch the tool again, we'll pick our start point, we'll pick our endpoint and then my Ortho is helping me grab my direction.

Let's back up a little bit. We'll center this on screen. Now, examples we've drawn are relatively simple sketches. I'm going to turn on a layer. I'm going to click on my Layer control. I'll select my Finished layer and we'll click on the screen. Hopefully, you can see the geometry we've constructed above is simply a starting point for creating the windows that we see below. By adding a few offsets and a couple of more arcs, we can create some fairly nice looking geometry.

Show transcript

This video is part of

Image for AutoCAD 2009: 2D Drafting Techniques
AutoCAD 2009: 2D Drafting Techniques

48 video lessons · 4089 viewers

Jeff Bartels
Author

 
Expand all | Collapse all
  1. 2m 36s
    1. Welcome
      1m 59s
    2. Using the exercise files
      37s
  2. 19m 58s
    1. Synchronizing settings
      5m 21s
    2. Understanding rollover tool tips
      2m 7s
    3. Making changes using Quick Properties
      2m 51s
    4. Finding answers with InfoCenter
      2m 36s
    5. Using Noun/Verb methodology
      3m 23s
    6. Using the Object Snap menu
      3m 40s
  3. 50m 1s
    1. Constructing circles using points and tangents
      7m 49s
    2. Creating arcs
      7m 14s
    3. Generating polylines
      6m 0s
    4. Creating boundaries
      2m 59s
    5. Exploring Hatch settings
      6m 33s
    6. Producing gradient fill hatches
      6m 27s
    7. Using points as markers
      4m 41s
    8. Drafting with construction lines and rays
      8m 18s
  4. 56m 21s
    1. Using the Edge function of Trim and Extend
      4m 39s
    2. Revising line work using Lengthen
      5m 18s
    3. Using the Trim function of Fillet and Chamfer
      4m 51s
    4. Offsetting through points
      6m 20s
    5. Removing geometry with the Break command
      4m 12s
    6. Modifying existing hatches
      5m 44s
    7. Aligning geometry
      5m 25s
    8. Adding and removing vertices from polylines
      5m 52s
    9. Dividing and measuring line work
      5m 20s
    10. Matching properties
      3m 46s
    11. Using the Clipboard functions
      4m 54s
  5. 17m 50s
    1. Using Apparent Intersection, Nearest, Node, and None
      5m 7s
    2. Finding parallels and extensions
      5m 28s
    3. Locating the midpoint between two points
      3m 40s
    4. Understanding the object "snap from"
      3m 35s
  6. 25m 37s
    1. Calculating areas
      5m 57s
    2. Organizing geometry using groups
      5m 44s
    3. Controlling visibility with Draw Order
      6m 23s
    4. Finding precise locations with the Geometric Calculator
      7m 33s
  7. 24m 59s
    1. Using the Crossing Polygon
      2m 35s
    2. Using the Fence
      3m 44s
    3. Adding and removing from selections
      5m 6s
    4. Selecting the last entity created
      4m 9s
    5. Cycling to select from stacked entities
      4m 6s
    6. Making selections based on criteria
      5m 19s
  8. 18m 59s
    1. Making an object's layer current
      1m 40s
    2. Freezing layers
      3m 47s
    3. Locking layers
      3m 19s
    4. Isolating layers
      2m 9s
    5. Preventing layers from plotting
      2m 53s
    6. Filtering layers
      5m 11s
  9. 15s
    1. Goodbye
      15s

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