Welcome to the world of CAD – In this first tutorial you will be learning the very basics of CAD. This 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 2010 and will work great for 2012. By the end of this level you will have the skills to develop basic 2D drawings and print them out to scale. For an introduction to what CAD is all about, check out my Blog post.
Let’s start at the beginning, these things you need to know, or the rest of it won’t make any sense at all. Make sure you have a very good understanding of this lesson before continuing. This lesson is longer than most (and not very exciting), but will cover important topics. Learn it, live it. Stick to it!
The X,Y coordinate system
Everything that you draw in AutoCAD is exact. It will be more accurate than you will ever need it to be. We’re talking 14 decimal points accurate. All objects drawn on the screen are placed there based on a simple X,Y coordinate system. In AutoCAD this is known as the World Coordinate 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).
Here is how it works:
AutoCAD uses points to determine where an object is located. There is an origin where it begins counting from. This point is (0,0). Every object is located in relation to the origin. If you were to draw a line straight out to the right from the origin, this would be considered the positive X-axis. If you were to draw a line straight up, this would be the positive Y-axis. The picture above shows a point located at (9,6). This means that the point is 9 units over in the X-axis and 6 units up in the Y-axis. When you are working with points, X always comes first. The other point shown is (-10,-4). This means that the point is 10 units in the negative X-axis (left) and 4 units in the negative Y-axis (down).
A line has two points, a start point and an end point. AutoCAD works with the points to display the line on the screen. Move your cursor over the picture above and you will see line drawn from the absolute points of (-10,-4) to (9,6).
Most of the time you will not have an indication of where the origin is. You may need to draw a line from the endpoint of an existing line. To do this you use relative points. These work the same way, but you have to add the @ symbol (shift+2) to tell AutoCAD that this next point is relative from the last point entered.