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Software Guides
Introduction to AutoCAD
Information and Learning Resource Services Ashan Kalpage
11/5/2001
Introduction to AutoCAD 2000
1.
Starting AutoCAD .......................................................p1
1.1. The AutoCAD window .........................................p2
2.
Coordinate Systems...................................................p3
2.1. Absolute and Relative Coordinates .....................p3
3.
2D Drawings................................................................p4
3.1. Drawing Lines.......................................................p4
3.2. Drawing Circles ...................................................p4
3.3. Drawing Arcs.......................................................p4
3.4. Drawing Ellipses..................................................p4
4.
Frequently used commands ......................................p4
4.1. Extending objects ................................................p4
4.2. Object Snap ........................................................p5
4.3. Mirroring ..............................................................p6
1. STARTING AUTOCAD To open AutoCAD click on the Start button and select Middlesex University local software, Graphical Applications and then click on AutoCAD 2000. When AutoCAD starts, a startup dialog box is displayed. The dialog box provides four ways to start a drawing.
Open an existing drawing
Start a drawing using a template chosen from a list
Open a new drawing with the aid of wizards
Start a new drawing from scratch. This is a quick and easy way to begin a new drawing
1
1.1
The AutoCAD window
Once you have started AutoCAD by selecting one of the four methods described, the AutoCAD window opens. The following figure shows the main parts of the AutoCAD window.
Draw toolbar
Menu bar
Standard Toolbar
Modify toolbar
Crosshairs
Command Window
Menu Bar: Contains the default AutoCAD menus. Standard: Toolbar
This contains the frequently used buttons such as Zoom, Undo and Redraw. It also has the Microsoft Standard buttons
Draw and Modify Toolbars
These toolbars provide you with the common draw and modify commands.
Crosshairs The crosshairs are controlled by the mouse, to locate points and select and draw objects. Command Window
The command window displays messages and prompts. In AutoCAD there are three ways of initiating commands: • • •
Click a button on a toolbar Choose an item from a menu Enter the command on the command line
2
2.
COORDINATE SYSTEMS
There are two coordinate systems in AutoCAD. 1)
The Cartesian coordinate system has two axes X, Y for 2D drawings and 3 axes X, Y, Z for 3d drawings. By entering coordinate values you indicate a points distance and its direction along the X, Y, Z axes relative to the origin.
2)
The Polar coordinate system uses an angle and a distance to locate a point. To enter a Polar coordinate, we first select a point and then enter a distance and an angle. For example if we were to specify a point 8 units from the origin at an angle of 30 degrees we would enter 8<30. In AutoCAD you are automatically in the World Coordinate system (WCS) when you start a new drawing. That is, the X axis is horizontal and the Y axis vertical and the point of origin is at the left lower most corner of the drawing area. Drawing 2d objects in AutoCAD is equivalent to producing drawings on a graph paper with relation to X, Y coordinates.
2.1
Absolute and Relative Coordinates
Absolute coordinate values are based on the origin (0,0). Relative coordinate values are based on the last point entered. For example if we were to draw a line beginning at X=2, Y=4 and ending at X=4, Y=6 using absolute coordinate, we would enter the following at the command prompt:
We may use relative coordinates when we know the position of a point in relation to the previous point. We use the @ symbol when specifying relative coordinates. For example the line which was drawn using absolute coordinates, can also be drawn using relative coordinates by typing the following at the command prompt:
3
3.
2D DRAWINGS
3.1
Drawing lines
A line is one of the easiest objects to draw. To draw a line in AutoCAD you must specify a start point and an end point. To draw a line 1
From the drawing menu choose line, or type line at the command prompt.
2
Specify the start point
3
Then specify the endpoint
4
Finally press the ENTER key to complete the line.
The offset command can be used to create copies of a line offset at a specified distance. This is done by typing, offset, at the command prompt. Then enter the offset distance and select the line or object to offset. Finally select the side or point to offset.
3.2
Drawing circles
There are several ways of drawing circles in AutoCAD. The easiest way to do this is to specify the centre of the circle and the radius
3.3
Drawing Arcs
It is possible to construct arcs in different ways. The default method of creating an arc is by defining 3 points (the start, Centre and end point). It must be noted that, AutoCAD draws arcs counterclockwise.
3.4
Drawing Ellipses
To draw an ellipse in AutoCAD you have to first define the centre of the ellipse and then the end points of the first axis followed by the distance of the second axis.
4.
FREQUENTLY USED COMMANDS
Apart from the commands that draw lines and other shapes, there are several commands in AutoCAD that help create drawings more effectively. Several of these are explained below.
4.1
Extending objects
You can extend objects so that they end exactly at the boundary defined by another object.
4
1) Type extend at the command prompt 2) Select a boundary up to which the object is to extend 3) Select the object to extend
Boundary selected
Objects to extend selected
4.2
Result
Object Snap
During drawings it is sometimes necessary to snap the cursor to other objects such as the end point of a line or the centre of a circle. The following table lists several object snaps that are frequently used in AutoCAD.
Object Snap
Command line
Snaps to
Endpoint
END
Object end points
Midpoint
MID
Object midpoint
Intersection
INT
Object Intersection
Centre
CEN
Centre points of circles, arcs and Ellipses
Quadrant
QUA
Closest quadrant of arcs, circles and ellipses
Perpendicular
PER
Object points forming a perpendicular alignment
5
4.3
Mirroring
It is sometimes useful to mirror an object around a mirror line, which is defined by two points. After mirroring you may retain or delete the original object.
Object selected using using a window
Mirror line defined
6
Result, with the original object retained
Introduction to AutoCAD
Information and Learning Resource Services Ashan Kalpage
11/5/2001
Introduction to AutoCAD 2000
1.
Starting AutoCAD .......................................................p1
1.1. The AutoCAD window .........................................p2
2.
Coordinate Systems...................................................p3
2.1. Absolute and Relative Coordinates .....................p3
3.
2D Drawings................................................................p4
3.1. Drawing Lines.......................................................p4
3.2. Drawing Circles ...................................................p4
3.3. Drawing Arcs.......................................................p4
3.4. Drawing Ellipses..................................................p4
4.
Frequently used commands ......................................p4
4.1. Extending objects ................................................p4
4.2. Object Snap ........................................................p5
4.3. Mirroring ..............................................................p6
1. STARTING AUTOCAD To open AutoCAD click on the Start button and select Middlesex University local software, Graphical Applications and then click on AutoCAD 2000. When AutoCAD starts, a startup dialog box is displayed. The dialog box provides four ways to start a drawing.
Open an existing drawing
Start a drawing using a template chosen from a list
Open a new drawing with the aid of wizards
Start a new drawing from scratch. This is a quick and easy way to begin a new drawing
1
1.1
The AutoCAD window
Once you have started AutoCAD by selecting one of the four methods described, the AutoCAD window opens. The following figure shows the main parts of the AutoCAD window.
Draw toolbar
Menu bar
Standard Toolbar
Modify toolbar
Crosshairs
Command Window
Menu Bar: Contains the default AutoCAD menus. Standard: Toolbar
This contains the frequently used buttons such as Zoom, Undo and Redraw. It also has the Microsoft Standard buttons
Draw and Modify Toolbars
These toolbars provide you with the common draw and modify commands.
Crosshairs The crosshairs are controlled by the mouse, to locate points and select and draw objects. Command Window
The command window displays messages and prompts. In AutoCAD there are three ways of initiating commands: • • •
Click a button on a toolbar Choose an item from a menu Enter the command on the command line
2
2.
COORDINATE SYSTEMS
There are two coordinate systems in AutoCAD. 1)
The Cartesian coordinate system has two axes X, Y for 2D drawings and 3 axes X, Y, Z for 3d drawings. By entering coordinate values you indicate a points distance and its direction along the X, Y, Z axes relative to the origin.
2)
The Polar coordinate system uses an angle and a distance to locate a point. To enter a Polar coordinate, we first select a point and then enter a distance and an angle. For example if we were to specify a point 8 units from the origin at an angle of 30 degrees we would enter 8<30. In AutoCAD you are automatically in the World Coordinate system (WCS) when you start a new drawing. That is, the X axis is horizontal and the Y axis vertical and the point of origin is at the left lower most corner of the drawing area. Drawing 2d objects in AutoCAD is equivalent to producing drawings on a graph paper with relation to X, Y coordinates.
2.1
Absolute and Relative Coordinates
Absolute coordinate values are based on the origin (0,0). Relative coordinate values are based on the last point entered. For example if we were to draw a line beginning at X=2, Y=4 and ending at X=4, Y=6 using absolute coordinate, we would enter the following at the command prompt:
We may use relative coordinates when we know the position of a point in relation to the previous point. We use the @ symbol when specifying relative coordinates. For example the line which was drawn using absolute coordinates, can also be drawn using relative coordinates by typing the following at the command prompt:
3
3.
2D DRAWINGS
3.1
Drawing lines
A line is one of the easiest objects to draw. To draw a line in AutoCAD you must specify a start point and an end point. To draw a line 1
From the drawing menu choose line, or type line at the command prompt.
2
Specify the start point
3
Then specify the endpoint
4
Finally press the ENTER key to complete the line.
The offset command can be used to create copies of a line offset at a specified distance. This is done by typing, offset, at the command prompt. Then enter the offset distance and select the line or object to offset. Finally select the side or point to offset.
3.2
Drawing circles
There are several ways of drawing circles in AutoCAD. The easiest way to do this is to specify the centre of the circle and the radius
3.3
Drawing Arcs
It is possible to construct arcs in different ways. The default method of creating an arc is by defining 3 points (the start, Centre and end point). It must be noted that, AutoCAD draws arcs counterclockwise.
3.4
Drawing Ellipses
To draw an ellipse in AutoCAD you have to first define the centre of the ellipse and then the end points of the first axis followed by the distance of the second axis.
4.
FREQUENTLY USED COMMANDS
Apart from the commands that draw lines and other shapes, there are several commands in AutoCAD that help create drawings more effectively. Several of these are explained below.
4.1
Extending objects
You can extend objects so that they end exactly at the boundary defined by another object.
4
1) Type extend at the command prompt 2) Select a boundary up to which the object is to extend 3) Select the object to extend
Boundary selected
Objects to extend selected
4.2
Result
Object Snap
During drawings it is sometimes necessary to snap the cursor to other objects such as the end point of a line or the centre of a circle. The following table lists several object snaps that are frequently used in AutoCAD.
Object Snap
Command line
Snaps to
Endpoint
END
Object end points
Midpoint
MID
Object midpoint
Intersection
INT
Object Intersection
Centre
CEN
Centre points of circles, arcs and Ellipses
Quadrant
QUA
Closest quadrant of arcs, circles and ellipses
Perpendicular
PER
Object points forming a perpendicular alignment
5
4.3
Mirroring
It is sometimes useful to mirror an object around a mirror line, which is defined by two points. After mirroring you may retain or delete the original object.
Object selected using using a window
Mirror line defined
6
Result, with the original object retained
