AutoCAD For Dummies. Ralph Grabowski

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СКАЧАТЬ a minute! I want to draw a map of the known universe! If I draw full size, where am I going to find a sheet of paper big enough to print it — and who will help me fold it?”

      Trust me. All will become clear shortly.

      DRAFTING ON PAPER VERSUS ELECTRONICALLY

      If you’ve ever done paper-and-pencil drafting (and there are fewer and fewer of us left who have), you’ll find that AutoCAD’s electronic paper works backward from dead-tree paper.

       Dead-tree paper: In the (distant) past, we considered the approximate size of the object that we were drawing by hand and the views we wanted, selected a suitable sheet of paper from a set of standard sizes, and then scaled the drawing of the object to suit the sheet of paper. We were constantly translating sizes between the real-world object and our drawing of it. The height of text and the size of the components in dimensions were fixed. Again, scales were selected from a list of preferred values, such as 1:2. You rarely saw a paper drawing at a scale of, say, 1:2.732486921.

       Electronic paper: Now we draw everything full size and then tell the PLOT command to grow or shrink things accordingly. This approach is much easier because we never have to translate sizes. Chapters 13–16 show you how AutoCAD now makes text and dimension sizing extremely simple.

“Okay,” you’re saying, “I understand that I need to print my drawings at a scale acceptable to the printer and discipline I work in. But when I’m drawing stuff full size, when do I need to worry about the scale factor?” Grab yourself a nice mug of cocoa and settle down ’round the fire because I’m going to tell you. By now you know (because I’ve told you so) that you draw real things full size, but drawings contain other things that are not real, such as text, dimensions, hatch patterns, title blocks, dash-dot linetypes, and so forth. And those nonreal things need to be legible on your plotted drawing.

      Say, for example, you draw a plan of your big garage, and now you want to plot it on an 11-x-17-inch sheet of paper. No problem; just tell the PLOT command to scale everything down by a scale factor of 1:24, which architects would commonly represent as 1/2″=1′0″.

      Oops, problem. Text annotations are typically about 3/32″ or 1/8″ high. Now, if you draw your 6-inch–wide wall full size, put a 1/8″-high title beside it, and then print the drawing at a scale of 1:24, the wall itself will measure 1/4″ on the sheet, and the note will be an illegible little speck beside it. You fix it by making the text 24 times larger, or 3 inches tall, so that it scales down to the correct size when plotted. See, sometimes two wrongs do make a right. Unusually, it takes three, although three rights make a left and two Wrights made an airplane.

      DRAWING SCALE VERSUS DRAWING SCALE FACTOR

      CAD users employ two different ways of talking about a drawing’s intended plot scale: drawing scale and drawing scale factor.

      Drawing scale is the traditional way of describing a scale: “traditional” because it existed long before CAD came to be. Drawing scales are expressed with an equal sign or colon: for example, 1/8″ = 1′0″, 1:20, or 2:1. You can translate the equal sign or colon as “corresponds to.” In all cases, the measurement to the left of the equal sign or colon indicates a paper measurement, and the number to the right indicates a real-world measurement. A metric drawing scale is usually expressed without units, as a simple ratio. Thus, a scale of 1:20 means 1 unit on the plotted drawing corresponds to 20 units in the real world.

      Drawing scale factor is a single number that represents a multiplier, such as 96, 20, or 0.5. The drawing scale factor for a drawing is the conversion factor between a measurement on the plot and a measurement in the real world.

The “Drawing scale versus drawing scale factor” sidebar explains how you arrive at the scale factor, but this isn’t an issue until it comes time to annotate your drawing. I cover noncontinuous linetype scaling in Chapter 9, text sizing in Chapter 13, dimensions in Chapter 14, and crosshatching in Chapter 15. The good news is that AutoCAD can now take care of all this automatically, but a well-placed rumor has it that there may still be a few drawings out there that did it the old way, so I cover both methods in the appropriate chapters.

      

You shouldn’t just invent some arbitrary scale based on what looks okay on whatever size paper you happen to have handy. Most industries work with a small set of approved drawing scales that are related to one another by factors of 2 or 5 or 10. If you use other scales, you’ll be branded a clueless newbie, at best. At worst, you’ll have to redo all your drawings at an accepted scale.

      

The SCale command covered in Chapter 11 has nothing to do with ladders, fish, or setting drawing scales or scale factors!

Table 4-1 lists some common architectural drawing scales, using both imperial and metric systems of measure. The table also lists the drawing scale factor corresponding to each drawing scale and the common uses for each scale. If you work in industries other than those listed here, ask drafters or coworkers what the common drawing scales are and for what kinds of drawings they’re used.

TABLE 4-1 Common Architectural Drawing Scales

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Drawing Scale	Drawing Scale Factor	Common Uses
1/16″ = 1′-0″	192	Large-building plans
1/8″ = 1′-0″	96	Medium-sized building plans
1/4″ = 1′-0″	48	House plans
1/2″ = 1′-0″	24	Small-building plans
1″ = 1′-0″	12	Details
1:200	200	Large-building plans
1:100	100	Medium-sized building plans
1:50	50	House plans
1:20	20	Small building plans
1:10