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Logon2cad provides CAD Conversion Services, 3D Modeling services, 3D rendering services, Character animation services, CAD drafting services, Character design services, Character modeling services |
Drawing and Editing |
I've talked about organizing drawings and customizing AutoCAD, but so far I've skirted most of the specifics of how drafters should create drawings in AutoCAD. Those who are interested in some of the gory details can read on. Objects are the indivisible units of an AutoCAD drawing. Objects come in several flavors, the most popular of which are line, arc, polyline, circle, and text string. Every AutoCAD objectpossesses, in addition to its geometric definition, a group of properties. The most important of these for our purposes are layer, linetype, and color. The fundamental purpose of layers is to group related objects: columns go on one layer, beams on another layer, grid lines on still another layer, and so on. By grouping objects logically on layers, the drafter can choose what to show on the screen or on the plot, since turning off a layer makes all objects on that layer invisible. Linetypes are the dash-dot patterns that a drafter uses to show a grid line, match line, footing, or other hidden line. Line color determines not only the color of objects on the screen (which helps the drafter identify what layer an object is on), but also their thicknesses on plots. That's because in AutoCAD you control plotted lineweight by mapping each color to a pen or line thickness. AutoCAD provides two ways to control the color and linetype of each object. In the absence of instructions to the contrary, each object inherits the color and linetype of the layer on which it resides. The drafter can, however, give objects explicit colors or linetypes that override the settings of their layers. In general, controlling the color and linetype of each object by layer is good. Assigning explicit color and linetype to objects usually is bad. Drawing precision is much more important in CAD than it is in manual drafting, because a lack of precision makes later editing, hatching, and dimensioning tasks more time-consuming. AutoCAD offers many methods for ensuring precision, including object snaps (grabbing the endpoints, midpoints, intersections, etc. of existing objects) and snap (constraining points to an imaginary Cartesian grid). A good CAD drafter will be familiar with these and other methods and will almost never specify a point without using one of them. AutoCAD provides several ways of grouping objects into a single "meta-object", and accomplished CAD drafters use these features extensively. Polylines join a series of connected lines and arcs that belong together. Associative dimensions group all the pieces of a dimension (witness lines, dimension line, ticks or arrows, and text) together. Blocks are groups of objects that get reused in one or more drawings. Blocks can include attributes, which are variable text fields that the drafter fills in each time he uses the block. An xref is a special kind of block that resides in a separate file and updates automatically when the drafter edits the external file. Drafters spend much more time editing existing objects than they do creating new ones, and as a result, efficient object selection is critical to CAD productivity. AutoCAD has a mind-boggling array of options for selecting objects by location in the drawing or by properties. Good CAD drafters are familiar with the full range of selection options and know how to select objects with a minimum of picks. Mediocre drafters tend to select objects one by one. Most computer displays are smaller than E-size sheets, so all CAD programs include a way to zoom in or out on the drawing and pan around it. AutoCAD has enough zoom options to keep a George Lucas happy, and once again, the accomplished CAD drafter masters most of them so that navigating around in a drawing is as efficient as possible. When working in large drawings, it's important to understand the difference between a screen redraw and a regeneration. Good CAD drafters know how to keep the number and time of regenerations to a minimum. As I mentioned earlier, layers also provide control over what appears on the screen, and all drafters should be completely familiar with the differences among the layer options turning off, freezing, and locking. Text styles and dimension styles are the keys to efficient, consistent creation of text and dimensions in AutoCAD. A text style definition includes the font, width factor, and perhaps height. A dimension style definition captures a group of dimension variable settings and stores them under a name. Dimension styles make creating and controlling dimensions much easier, but many CAD drafters haven't yet mastered this important feature because of lack of training and/or lack of office-specific customization. |
