X-Y CO-ORDINATE SYSTEM, INPUTTING POINTS THE AUTOCAD

X-Y CO-ORDINATE SYSTEM, INPUTTING POINTS THE AUTOCAD

Welcome to the world of CAD - In this tutorial you will be learning the basics of AutoCAD. The course is designed so that the commands and instructions should work on almost any version of AutoCAD, although this version is designed specifically for AutoCAD 2007. By the end of this level you will have the skills to develop basic 2D drawings and print them out to scale.

The X,Y co-ordinate system

Everything that you draw in AutoCAD is exact. It will be more accurate than you will ever need it to be. All objects drawn on the screen are placed there based on a simple X,Y co-ordinate system. In AutoCAD this is known as the World Co-ordinate System (WCS). You must understand this to know how to put things where you want them. (3-D work has an added axis, the Z-axis, but this is not covered in this lesson.) Below is a diagram showing you how this system works (place your mouse on the diagram for more info).

In order to work effectively with AutoCAD, you have to work with this system. Until you are comfortable and familiar with it, learning AutoCAD will be more of a chore. My experience in teaching is that the better a student is with co-ordinates, the better CAD draftsperson they will become..

Angular Measurement

AutoCAD measures angles in a particular way also. Look at the diagram below and then place your mouse on it to see how this is done.

When drawing lines at an angle, you have to begin measuring the angle from 0 degrees, which is at the 3 o'clock position. If you drew a line at 90 degrees, it would go straight up. The example above (when you move your mouse over it) shows a line drawn at +300 degrees, or -60 degrees.

You might not always have an obvious reference point for 0 degrees. Look at the example below and place your mouse on the image to find out angle in question.

In this example, you are given information about the lines, but not the angle AutoCAD needs to draw the line from the start point. What you are given though, is (a) the knowledge that 0° is at the 3 o'clock position (b) the knowledge that 180° is at the 9 o'clock position and (c) the angle between 180° and the line you want to draw is 150°. With this information, you can figure out what angle you need. Here is a fool-proof way of getting the angle you need:

1.) Start at the 0° position and measure counter-clockwise (+) to 180°.

2.) From 180°, measure clockwise 150°.

3.) Consider that you just went +180-150 and use that as an equation: +180-150=30

4.) Now you can draw your line using Polar Co-Ordinate (discussed below)

Icons, Keystrokes and Menus

There are many ways to do things in most windows programs. AutoCAD is no exception. Everyone will develop a way that works best for him or her. In this course, we will primarily be working with the keystroke commands. The reason for this is because they will work in most AutoCAD versions (including DOS versions), and in some other CAD programs. The icons work well, but as you will see, icons can be placed anywhere on the screen and can be difficult to find quickly. The pull-down menus will access almost all commands, but are a slower way of doing things.

Example: If you want to draw a line, you can do it a few ways:

•    At the command line type: LINE (or) L and press the ENTER key.

•    Select the line icon  from the DRAW toolbar.

•    Select Draw > Line from the pull-down menu.

All three approaches will do the same thing: prepare AutoCAD to draw a line where you tell it.

AutoCAD is a popular program because it can be customized to suit an individual's needs. The toolbars are a good example of this. You can have the toolbars you use most often on the screen all the time. You can easily make them go away so that you have more drawing space. You can also customize them so you have the most common commands on one toolbar. For example, the dimensioning toolbar is one that you will not want taking up space on your screen while drawing, but is very handy when you're dimensioning your drawing.

The AutoCAD Screen

Move your cursor around the image above to find the names of various areasof the screen.

•    Title Bar - This will show you what program you are running and what the current filename is.

•    Pull-down menus - These are the standard pull-down menus through which you can access almost all commands.

•    Main toolbar - This has most of the standard Windows icons, as well as the most common AutoCAD commands.

•    Property toolbar - This toolbar gives a way to quickly modify an object's properties, such as layer and linetype

•    Floating toolbar - This is a toolbar that can be moved around the screen, or 'docked' as the main toolbar is.

•    Drawing space - This is where you draw. You have an almost infinite area to draw and this is just a 'section' of the entire space.

•    Scrollbars - These work like in other windows programs. You can also use the PAN command to move around your drawing.

•    WCS Icon - This is here to show you which direction positive X and positive Y go. The W means you're in the World Co-ordinate System. (It can be changed to a User Co-ordinate System.)

•    Status Bar Tray Icons - These icons give you updates on items like reference files program updates and print status.

•    Command line - When you type a command, you will see it here. AutoCAD uses this space to 'prompt' you for information. It will give you a lot of information and tell you where you are in the command. Watch this line while learning.

•    Status bar - This allows to see and change different modes of drawing such as Ortho, Osnaps, Grid, Otrack, etc.

SCREEN BASIC AUTOCAD TERMINOLOGY

Command Work & Assignment

Your first drawing assignment will be to use the drawing commands in conjunction with the co-ordinate system defined above. This is a basic assignment, but it is very important to understand how to give the program accurate information. You will use the following commands:

Object Snaps

Suppose you want to draw a line from the center of the circle to the middle of the vertical line you extended earlier. AutoCAD has a feature that makes this very easy. These are the Object Snaps (or Osnaps "Oh-Snaps"). Type OS <ENTER> . You will see this dialog box appear.

You may also see a toolbar with these Osnaps as shown below.

Steps:

Start AutoCAD and a new drawing by using the menu option File > New. You will see a dialog box open that asks you to select a template drawing to use (as shown below):

Select the "acad.dwt" template file (more about those in a Later lesson and press the Open button to continue to the drawing screen.

Once there, type in Z <ENTER> E <ENTER> this will zoom into to the extents of the drawing area and make it easier to see what you are drawing (NOTE: nothing will appear to happen).

For all lessons on this level, make sure that you do not have Dynamic Input turned on. You can check this on the status bar. Make sure  (the DYN button) isn't depressed. This is a new system of entering points that will be covered in a later lesson, but personally I find them less convenient and can affect you computer's resources.

Start the LINE command (as explained in the table above) and draw a line from 1,2 to 3,2 to 3,4 to 1,4 Press enter after each point. (*Remember to watch the command line as you do this.) For the last line, you can either type in 1,2 or C to close the line back to the first point you entered. You have just drawn a 2" square using absolute co-ordinates.

If you make a mistake, you can use the undo icon,  press U or press CTRL+Z.

You can also use the ERASE command to get rid of lines you don't want.

Next draw a similar box using relative co-ordinates. Start the LINE command and begin at point 4.5,2. From there draw a line two units to the right by typing @2,0 (this means 2 units in the X direction, 0 units in the Y direction based on the last point you entered). Next type @0,2 then @-2,0 then @0,-2 to finish the box. (Remember to press enter after each point.)

Now erase the last box you just drew. Start the ERASE command and then select the lines you want to erase. Then press <enter>. Now redraw the box for more practice!

Draw a third box using polar co-ordinate input. Start the LINE command and begin at point 8,2 then enter. Type @1<45 to draw the first line. Next enter @1<135 then @1<225 then @1<315 (or C to close). What you have just done is drawn a line 1 unit long at 45o, then another at 135o and so on.

Start the CIRCLE command and add a circle that has a center point at 7,6 with a radius of .75 (Watch the command line for instructions).

To finish the drawing, try putting a 10"x7" border around the page starting at 0,0 using the any of the methods shown above (relative, absolute or polar).

When you have done the assignment, print (or plot) it out. To do this, bring up the plot dialog box using any method explained above (plot <enter> will work). Set it up to print as shown below. Follow these steps for a successful plot (see diagram below)

1.    Select your printer - laser or inkjet will work fine.

2.    Select the paper size - "Letter" ( 8-1/2" x 11") is needed in this case.

3.    For the "Plot Area", select "Extents" - that will plot everything you drew.

4.    Select the checkbox to "Center the Plot" on your sheet of paper (looks better).

5.    If "Fit to Paper" is selected by default, uncheck it and select a scale of 1 inch to 1 paper unit. This will make your printout 'life-sized'.

6.    Now Preview your drawing. I strongly recommend that you preview EVERY drawing you will ever draw in AutoCAD - a lot can go wrong, so you don't want to waste paper (especially when you're using expensive 3'x4' sheets!).If your preview looks good, cancel out of it by clicking on the large red X icon.

7.    If you're sure that everything's ok (this is where good habits begin), press the OK button.

Note: You may have to change the paper size in your printer (Use the Windows printer settings to do this.) You may also have to change the rotation or origin of the plot. Check the Landscape radio button in the Drawing Orientation section.

If everything worked out, you should be able to measure your drawing and have it exactly the way you drew it (a couple of 2" squares, an angled 1" square and a 1-1/2" circle).

Layers and Dimensioning

Looking at the Dialog Box, you will see a lot of information. Notice the button beside Make Current on it. Below it is the name of the current layer you are drawing on. The main window gives you information about each particular layer. At this point, you want to be concerned with the 'Name', 'On' (light bulb) and 'Color' (colored square) columns as well as the 'New' button.

Now you have the dialog box on your screen, click the 'New' button. This will create a new layer and give you an opportunity to name it. Name this layer TEXT. Click on the small box towards the right and select yellow for the color. Create another layer and call this one DIM (for dimensions), and make its color red. Finally, create a third layer and call it OBJECT and make its color green. You have just created three new layers in your drawing. Highlight the TEXT layer and then press the 'Make Current' button. This makes the TEXT layer current and anything you draw will be placed on that layer. Your Dialog box should look like the one above. If it does, press OK to close the dialog box.

More about Layers

 

In the Layer Properties Manager, you will notice that each layer can have a number of specific properties.

•    Status: Displays the current state of the layer. In this example, the green check means that Objects is the current layer.

•    Name: The name of the layer. Give layers understandable names.

•    On: If a layer is 'On' it means that it is visible (but objects can still be erased when the 'Select > All option is used).

•    Freeze: A layer is not visible and cannot be deleted.

•    Lock: Layer is visible, but cannot be modified.

•    Color: A specific color for everything on that layer.

•    Linetype: A specific linetype (hidden, center, etc) for the layer.

•    Lineweight: The visible width of the objects on that layer.

•    Plot: A defined color for the plotter to use on that layer.

•    Plot (yes, two colomns use the same name: Switch on or off if that layer is plotted.

•    Description: A user-defined description for the layer.

Here are the ones you'll be using in this lesson.

Linear dimensions are used for dimensioning either horizontal or vertical distances.

Aligned dimensions will measure the actual length of an angled line.

Radius dimensions will give you the radius of either arcs or circles.

Diameter dimensions are used on circles.

Angular dimensions will measure the angle between two lines that you pick.

Baseline dimensions are a special type that will automatically stack dimensions along one plane as you pick points.