Assignment No.5 Dimensioning Text and Plot Commands
DEPARTMENT OF AUTOMOBILE ENGINEERING COMPUTER AIDED DRAFTING
Assignment No.5 Dimensioning Text and Plot Commands
Before you start the drawing-setup process, you need to make only two initialdecisions about your new drawing:
What system of measure — metric or Imperial — will you use?
What drawing units will you use?
AutoCAD is extremely flexible about drawing units; it lets you have them your way. Usually, you choose the type of units that you normally use to talk about whatever you’re drawing: feet and inches for a building, millimeters for a metric screw or mechanical drawing, and so on.During drawing setup, you choose settings for length units. AutoCAD’s length unit types are as follows:
Architectural units are based in feet and inches and use fractions to represent partial inches: for example, 12'3 1/2".
Decimal units are unitless — that is, they’re not based on any particular real-world unit. With decimal units, each unit in the drawing could represent an inch, a millimeter.
Engineering units are based in feet and inches and use decimals to represent partial inches: for example, 12'3.5".
Fractional units, like decimal units, are unitless and show values as fractions rather than decimal numbers: for example 15 1/2.
Scientific units, also unitless and show values as exponents, are used for drawing really tiny or really large things. If you design molecules or galaxies, this is the unit type for you. Examples would be 15.5E+06 (which is 15,500,000) and 15.5E–06 (which is 0.0000155).
AutoCAD’s angle unit types are as follows:
Decimal Degrees show angles as decimal numbers and are by far the easiest to work with, if your type of work allows it.
Deg/Min/Sec is based on the old style of dividing a degree into minutes and minutes into seconds.
Grads and Radians are mathematically beautiful (so we’re told) but are not widely used in drafting. Apparently, the French artillery uses grads
Surveyor’s Units type is similar to Deg/Min/Sec but uses quadrants (quarter circles) rather than a whole circle.
When you use dash-dot linetypes and hatching in a drawing, it matters to AutoCAD whether the drawing uses an Imperial (inches, feet, miles, and so on) or metric (millimeters, meters, kilometers, and so on) system of measure. The MEASUREINIT and MEASUREMENT system variables control whether the linetype and hatch patterns that AutoCAD lists for you to choose from are scaled with inches or millimeters in mind as the plotting units.
The Drawing Units dialog box. You can find it in file menu
Adding Dimensions to a Drawing.
We start off with an exercise to introduce AutoCAD’s dimensioning functionality by creating linear dimensions that show the horizontal or vertical distance between two endpoints:
1. Start a new drawing, using the acad.dwt template file.
This step creates a drawing that uses imperial units, even if your default installation uses metric. It saves us lazy writers from having to duplicate our instructions for metric users.
2. Use the Line command to draw a non-orthogonal line.
3. Set a layer that’s appropriate for dimensions as current.
Okay, you started from a blank template, so it doesn’t have specific layers, but we included this step as a gentle reminder.
4. Start the DimLInear command by clicking the down arrow at the bottom of the Dimension button on the left side of the Annotate tab’s
Dimensions panel and click Linear, or type DLI and press Enter.
AutoCAD prompts you:
Specify first extension line origin or <select object>:
5. To specify the origin of the first extension line, snap to the lower-left endpoint of the line by using an ENDpoint object snap.
AutoCAD prompts you:
Specify second extension line origin:
6. To specify the origin of the second extension line, snap to the other endpoint of the line by using an ENDpoint object snap again.
AutoCAD prompts you:
Specify dimension line location or[Mtext/Text/Angle/Horizontal/Vertical/Rotated]:
7. Move the mouse to generate the type of dimension you want — horizontal or vertical — and then click wherever you want to place the dimension line.
8. Repeat Steps 4–7 to create another linear dimension of the opposite orientation (vertical or horizontal).
9. Click the line to select it.
10. Click one of the grips at an end of the line and drag it around.
AutoCAD provides several types of dimensions and commands for drawing them; most commands are shown in Figure these commands are found on the Dimensions panel of the Annotate tab on the Ribbon. If you can’t find the button you want, it’s probably hidden in the drop-down list, under the larger button on the left side of this panel. This panel remembers the last button you used, so at any given time, it may be displaying any one of the following buttons.
In the following list, the three characters (in parentheses) is the shortened command name (command alias) you can also enter:
Linear — DimLInear (DLI): Indicates the linear extent of an object or the linear distance between two points. Most linear dimensions are either horizontal or vertical, but you can draw dimensions that are rotated to other angles, too.
Aligned — DimAigned (DAL): Similar to linear dimensions, but the dimension line tilts to the same angle as a line drawn through the origin points of its extension lines.
Angle — DimANgle (DAN): Indicates the angular measurement between two lines, the two endpoints of an arc, or two points on a circle. The dimension line appears as an arc that indicates the sweep of the measured angle.
Radial — DimDIameter (DDI), DimRAdius (DRA): A diameter dimension calls out the diameter of a circle or an arc and a radius dimension shows the radius of a circle or an arc. You can position the dimension text inside or outside the curve; refer to Figure if you position the text outside the curve, AutoCAD draws (by default) a little cross at the center of the circle or arc. AutoCAD automatically adds the diameter and radius symbols to the appropriate dimension type.
Arc Lenth — DimARc (DAR): Measures the length of an arc as though it were stretched out straight and then applies a curved dimension line that’s concentric with the arc.
Jog — DimJOgged (DJO): When dimensioning arcs, it is standard drafting practice to create a dimension line that starts at the center of the arc and proceeds outward to the arc itself. A problem arises, however, when dimensioning an arc with a very large radius. The center may be at an inconvenient location where the dimension line would interfere with other geometry or, worse, it may be well beyond the edge of the final drawing. DimJOgged neatly solves this problem for you
Ordinate — DimORdinate (DOR): Applies X or Y coordinate values from an origin point. Certain types of mechanical parts can have a great many holes and other features. The drawing would become impossibly cluttered if you were to apply two traditional dimensions to show the X and Y locations of each detail. Common practice in this situation is to use ordinate dimensioning.
Quick dimension commands
Three dimensioning commands can help you place multiple dimensions very quickly. They’re found near the middle of the Dimensions panel of the Annotate tab on the Ribbon.
Continue — DimCOntinue (DCO): Having placed one linear dimension, you can now carry on to place a series of end-to-end dimensions.
AutoCAD automatically picks the end of the previous dimension as the start of the next one, so you need to pick the end of only the next one.
Base — DimBaseline (DBA): This one works much like DimCOntinue except that AutoCAD selects the start of the previous one as the start of the next one. You thus end up with a series of dimensions, all measuring from a common starting point.
Quick Dimensions — QDIM: Interestingly, this is one of the few dimensioning commands that doesn’t start with DIMxxx. When you invoke it, it invites you to select objects. The best bet usually is to use one or more window selections (pick from left to right), each of which completely surrounds several objects. Now, whenever you press Enter, AutoCAD automatically applies DimLInear dimensions wherever it can (and you might be surprised at some of those places
Opening the Dimension toolbar
1. Click the View tab on the Ribbon.
2. On the User Interface panel, click Toolbars.
3. Click AutoCAD or AutoCAD LT to display a list of classic toolbars.
4. Choose Dimension from the menu.
Creating dimension styles
If you do need to create your own dimension styles or you want to tweak existing ones, use the DIMSTYle command. You can invoke it by clicking the small, diagonal arrow in the lower-right corner of the Dimensions panel of the Annotate tab on the Ribbon. The Dimension Style Manager dialog box opens.
Editing Dimensions
After you draw dimensions, you can edit the position of the various parts of each dimension and change the contents of the dimension text. AutoCAD groups all parts of a dimension into a single object.
Editing dimension geometry
The easiest way to change the location of dimension parts is to use grip editing, Just click a dimension, click one of its grips, and maneuver away. You’ll discover that certain grips control certain directions of movement. Selecting a dimension displays grips generally at the text, the ends of the dimension lines, and the defpoints.
If you want to change the look of a component of a specific, individual dimension (for example, substitute a different arrowhead or suppress an extension line), use the Properties palette. All dimension settings in the New/Modify Dimension Style dialog boxes are available from the Properties palette when you select one or more dimensions.
Follow these tips for editing dimensions:
Use smart breaks. In manual drafting, it’s considered bad form to cross object lines (that is, real geometry) with dimension lines or extension lines, or to have anything cross a dimension line. Dimension Break (DIMBREAK) prompts you to select a dimension and then an object to break it. The wild aspect is that it’s a smart break
Use the DIMSPACE command. The Dimension Space (DIMSPACE) command applies a specified separation between existing linear or angular dimensions. Spacing dimensions equally — if you don’t use the DimBAseline command as they’re created — requires tedious manipulation with Snap Mode and the Move command.
Template
When you start in either the Drafting & Annotation workspace or the old AutoCAD Classic workspace, AutoCAD creates a new, blank drawing configured for 2D drafting. Depending on where you live (your country, not your street address!) and the dominant system of measure used there, AutoCAD will base this new drawing on one of two default drawing templates:
acad.dwt for the Imperial system of measure, as used in the United States
acadiso.dwt for the metric system, used throughout most of the rest of the galaxy(We use This)
When you explicitly create a new drawing, the Select Template dialog box, shown in Figure appears by default so you can choose a template on which to base your new drawing.
Using a suitable template can save you time and worry because many of the setup options are already set correctly for you. Follow these steps to create a new drawing from a template drawing:
1. Run the NEW command by pressing Ctrl+N or clicking the Application button and choosing New.
The Select Template dialog box appears.
2. Click the name of the template you want to use as the starting point for your new drawing and then click the Open button.
A new drawing window with a temporary name, such as Drawing2.dwg, appears. (The template you opened remains unchanged on your computer's hard drive.)
Depending on which template you choose, your new drawing may open in a paper space layout.
3. Press Ctrl+S or click the Application button and choose Save to save the file under a new name.
4. Make needed changes.
5. Save the drawing again.
Preciseliness:
Drawing precision is vital to good CAD drafting practice, even more than for manual drafting. In AutoCAD, a lack of precision makes editing, hatching, and dimensioning tasks much more difficult and time consuming. When we talk about drawing elements precisely, we mean using precision techniques and tools to specify points and distances with as much exactness as the program allows. Luckily, AutoCAD provides a comprehensive package of tools for this task. Table lists the more important AutoCAD precision techniques; along with visual cues to the status bar buttons you click to toggle certain features. Note that this list omits status bar buttons that don’t directly affect drawing precisely.
Grabbing points with object snap overrides
Object snap overrides:
Here’s how to draw precise lines by using object snap overrides:
1. Open a drawing containing some geometry, or start a new drawing and create some.
2. Turn off running object snap mode by clicking the OSNAP button on the status bar until the button appears to be dimmed and <Osnap off> appears in the command line.
AutoCAD prompts you to select the starting point of the line:
Specify first point:
Hold down the Shift key, right-click anywhere in the drawing area, and release the Shift key.
The Object Snap menu appears, as shown in Figure.
Text with Character:
It used to be said that "a picture is worth a thousand words," but with the current state Adding a few words to your drawing can save you from having to draw thousands of lines and arcs. AutoCAD’s annotative objects present a streamlined way to add notes, dimensions, and other annotations to drawings. In AutoCAD, adding text to a drawing is similar to adding it to a word processing
. Select an existing AutoCAD text style, or create a new style that includes the font and other text characteristics you want to use.
Just like a word processor, AutoCAD uses styles — collections of formatting properties — to control the appearance of drawing text. We explain text styles in the next section.
2. Make an appropriate layer current.
3. Run one of these commands to draw text:
• TEXT: Draws single-line text
• mText: Draws paragraph (also called multiline) text
4. Specify the text alignment points, justification, and (if necessary) height.
5. Type the text.
6. (Optional) For annotative text, assign additional annotation scales to the text you just typed, if desired.
Layout
Despite the infinitesimally small number of offices without a computer (or two) on every desk or in a pocket, many people still want or need to work with easily readable electronic drawings (can you spell P-D-F?) or dead-tree paper drawings. You may need to give hard-copy printouts or PDF files to less savvy colleagues who dont have AutoCAD, or to people on workshop or sites where relatively delicate computers wouldn’t survive long. You may want to print hard copies to review during your bus ride home. You may even find that checking drawings the old-fashioned way, with a hard-copy printout and a red pencil, turns up errors that managed to remain hidden on the computer screen.
Plotting originally meant creating hard-copy output on a device that was capable of printing on larger sheets, such as D size or E size (or A1 or A0 for the metrically inclined), that measure several feet (or a meter or more) on a side. These plotters often used pens to draw, robot-fashion, on large sheets of vellum or drafting film. The sheets could then be run through diazo blueline machines, which were copying machines that created blueline prints to create less-expensive copies. Nowadays, AutoCAD and most CAD users make no distinction between plotting and printing. AutoCAD veterans usually say plotting.
Follow these steps to make a simple, not-to-scale, monochrome (black-and-white) plot of a drawing:
1. Open the drawing in AutoCAD.
2. Click the Model tab to ensure that youre plotting the model space contents.
If you dont have the Model and Layout tabs displayed, click the Model button (not the MODEL/PAPER button) on the status bar.
3. Zoom to the drawing current extents.
Click the Zoom Extents button on the Navigation bar. (If necessary, click the tiny down arrow below the Zoom button, and choose Zoom Extents from the menu.) Or easier yet, type Z E (note the space between the letters) and then press Enter.
The extents of a drawing consist of a rectangular area just large enough to include all objects in the drawing.
4. Click the Plot button on the Quick Access toolbar.
The Plot dialog box appears, as shown in Figure.
5. In the Printer/Plotter area, select a device from the Name drop-down list.
If your computer has a generic printer attached to it, select Default Windows System Printer pc3. If you dont have a system printer connected, choose Microsoft XPS Document Writer. This step creates a file that can be viewed in Internet Explorer.