Part 2
Module 7: Circles and Arcs
Learning Outcomes
When you have completed this module, you will be able to:
- Describe the geometry of circles and arcs.
- Apply the CIRCLE and ARC commands to draw circles and arcs.
- Describe how to undo a command or redo an undo.
Geometry Lesson: Circles
A circle is defined as a closed curve in which all points are the same distance from its center point. The center point is a single XY coordinate.
A circle is 360 degrees and can be divided into four quadrants. All points on a circle are at a given distance from is center point. The distance between any of the points and the center is called the radius.
Study the drawings in Figure 7-1, 7-2, 7-3, and 7-4 for a description of the geometry of a circle.
Geometry Lesson: Arcs
An arc is defined as an open curve in which all points are the same distance from its center point. Study the drawings in Figure 7-5 and 7-6.for a description of the geometry of an arc.
AutoCAD Command: CIRCLE
The CIRCLE command is used to draw circles.
Shortcut: C
AutoCAD Command: ARC
The ARC command is used to draw arcs.
Shortcut: A
Command: ARC
Specify start point of arc or [Center]: C
Specify center point of arc: 3,4
Specify start point of arc: @0,-2
(Specifying the radius and the direction for the start point.)
Specify end point of arc or [Angle/chord Length]: A
Specify included angle: 180
Command:
WORKALONG: Drawing Circles and Arcs
Step 1
Start a new drawing using the template: 2D English.
Step 2
Save and name the drawing: AutoCAD 2D Workalong 07-1.
Step 3
Create layer: Object, color red. Set it as the current layer. (Figure Step 3)
Step 4
Using the figures and what you already leaned, draw the two lines shown in Figure Step 4B. (Figure Step 4A and 4B)
Step 5
Enter the ARC command, as shown below, to draw the arc. (Figure Step 5)
Command: ARC
Specify start point of arc or [Center]: C
(If possible, always draw arcs starting with the center point first.)
Specify center point of arc: 2.5, 5
(Enter the center point.)
Specify start point of arc: @4,0
(Enter the start point. Here the trick is to give AutoCad the start point and the radius of the arc at the same time)
Specify end point of arc or [Angle/chord Length]: A
Specify included angle: 90
(Enter the angle of the arc. In this case, it is 90 degrees.)
Command:
Step 6
Enter the CIRCLE command, as shown below, to draw the four circles to complete the drawing. (Figure Step 6A and 6B)
Command: CIRCLE
Specify center point for circle or [3P/2P/Ttr (tan tan radius)]: 3.5,6
(Since this is the first circle, enter an absolute coordinate for the center point.)
Specify radius of circle or [Diameter]: D
(Circles are usually dimensioned with diameters rather then a radius, enter D)
Specify diameter of circle: 0.65
Command: CIRCLE
(Press Enter or Space bar as that will repeat the last command.)
Specify center point for circle or [3P/2P/Ttr (tan tan radius)]: @1,0
(Notice here, since AutoCAD always remembers the lastpoint, use an @. The lastpoint was th