AutoCAD For Dummies. Ralph GrabowskiЧитать онлайн книгу.
with in the 1980s.
Part 2
Let There Be Lines
IN THIS PART …
Draw lines and other mostly linear objects, as well as the curvy bits.
Find out how to draw objects with precision.
Manage object properties.
Select and edit objects.
Set up a paper space layout in anticipation of printing.
Chapter 6
Along the Straight and Narrow
IN THIS CHAPTER
As you may recall from your crayon-and-coloring-book days, drawing is fun. Computer-aided drafting (CAD) imposes a little more discipline, but drawing with AutoCAD is still fun. Trust me on this one. In CAD, you usually start by drawing geometry from basic shapes — lines, circles, and rectangles — to construct the real-world object that you’re documenting.
For descriptive purposes, I divide the drawing commands into three groups:
Straight lines and objects composed of straight lines, covered in this chapter
Curves, which I explain in Chapter 7
Points, explained in Chapter 7 as well if you’re wondering what the point of all this is
After you’ve created some straight or curvy geometry, you’ll probably need to add descriptive elements, like dimensions, text, and hatching, but those come later (in Part 3). Or you may want to use straight and curvy geometry as the basis for some cool 3D modeling. I introduce you to that topic in Part 5. Your first task is to get the geometry right; then you can worry about labeling it.
Proper geometry creation also depends on creating objects that have the correct appearance. In Chapter 9, I show you how to create hidden lines, center lines, section lines, and other elements.
Drawing for Success
AutoCAD offers a wide range of tools that allow you to create designs in a virtual world that will be accurately manufactured or built in the real world. The 2D and 3D tools that you use require some upfront preparation to ensure that the designs you create are drawn precisely. Nothing is worse than spending time on a great design, only to find out that the objects you drew weren’t drawn at the correct size and that lines don’t intersect cleanly. Okay, I lied. Worse yet is that your imprecise drawing was used to program a CNC machining center or build a house and now the expensive parts don’t fit.
Here are a few important techniques to use when you draw objects:
Use precision tools to make sure objects intersect precisely and are drawn at the correct angle. Precision tools allow you to reference points on existing objects, constrain the cursor to a specific angle or snap distance, and quickly locate a point based on a distance and direction in which the cursor is moved. I cover precision techniques and tools in Chapter 8.
Understand the difference between command line and Dynamic Input coordinate entry. Second and next points entered at the command line are interpreted differently from those entered at the Dynamic Input tooltip. The second and next points entered at the Dynamic Input tooltip are formatted as polar and are relative to the previously entered coordinate value automatically, unlike at the command line where you must first type @ before the coordinate value for relative coordinates. AutoCAD’s Dynamic Input system displays a lot of the information at the cursor that you used to have to look down to the command line to see. To use Dynamic Input, press F12 to toggle it on and off.
Watch the command line. The command line at times displays additional information about the current command that’s not displayed in the Dynamic Input tooltip. This information might be the current text style or justification, or the active extend mode. I cover using the command line in Chapter 2.
Organize objects on layers. All the objects you draw should be placed on specific layers. For example, annotation objects that communicate design information might be placed on a Notes layer, and the lines that are used to represent a wall might be placed on a Walls layer. I cover layers in Chapter 9.
Introducing the Straight-Line Drawing Commands
As I harp on elsewhere in this book, CAD programs are designed for precision drawing, and you’ll spend a lot of time in AutoCAD drawing objects composed of straight-line segments. The rest of this chapter covers these commands, all of which are found on the Draw panel of the Home tab on the Ribbon. The icons in the left margin match those on the Ribbon:
Line: Draws a series of one or more visually connected straight-line segments; that is, the end of the current segment has the same coordinates as the start of the next segment. Although the lines look like they're physically connected, each segment (piece of a line with endpoints) is in fact a separate object with its own start and endpoints.
PLine: Draws a polyline, which is a series of straight- or curved-line segments (or both) connected as a single object. I’m cheating slightly here because I cover curvy components in Chapter 7, but I don’t want you to have to read about one command in two different places.
RECtang: Provides a convenient way to draw rectangles in a variety of ways as four right-angle polyline segments. AutoCAD has no actual rectangle object.
POLygon: Gives you a convenient way to draw a polyline of many sides in the shape of a regular polygon (a closed shape with all sides and all angles equal).
The following additional straight-line drawing commands, also available in AutoCAD LT, are found in the drop-down list below the Draw panel:
XLine: Draws a line (known as an ex-line or a construction line) that passes through a point at a specified angle and extends to infinity