Technical Drawing – Week I

1. Technical Drawing – Week I 2008-Fall

2. Overview • Instructor : Yavuz Keçeli • Time : Wed. 9:30~12:30 • Place : Sim. Center, CBT LAB • Evaluation : • Midterm Exam :30% • Homeworks :20% • Final Exam :50%

3. Course Outline • 1. Introduction to AutoCAD and drawing settings • 2. Drawing objects • 3. Modifying objects • 4. Object snapping • 5. Dimensioning • 6. Projections/ Isometric drawing • 7. Orthographic drawing • 8. Sectioning • 9. 3D drawing

4. Using the Drawing Editor

5. Using the Drawing Editor • Beginning a new drawing • File menu • New  • Command line • new  • Saving a document file • File menu • Save  • Save as…  • Command line • save  Save as…  • qsave  Save 

6. Using the Drawing Editor • Undoing operations • Simply Ctrl+Z • Command line • undo  • Enter the number of operations to undo or [Auto/Control/BEgin/End/Mark/Back] <Number>: • Mark and Back • The mark subcommand makes a special mark in the undo information, to which you can back up with the Back subcommand. This makes it easy to try an experiment and drop the whole thing if it does not work. • The Back subcommand will take the drawing back to the state it was when the most recent Mark subcommand is entered. Back will take you back one mark each time, and removes the Mark when it finds it. If there is no preceding Mark, the Back subcommand will ask if you want to undo everything. If you answer Yes, everything you did since entering AutoCAD will be undone. If you answer No, the Back subcommand will be ignored. A mark stops multiple UNDO operations if the number entered is greater than the number of operations since the mark.

7. Using the Drawing Editor • Undoing operations • Begin and End • The BEgin and End subcommands cause a group of commands to be treated as a single command for the purposes of U and UNDO. This feature is mainly intended for use with menus, especially through the Auto feature. • Auto • The Auto subcommand issues the prompt: • Enter UNDO Auto mode [ON/OFF] <current>: • Current is the present setting which is retained if you give a null reply. If Auto is ON, any item selected from a menu, no matter how complicated it is, will be treated as a single command, and will be completely undone by a single U. For instance the insertion of a door by using a menu macro, which could involve many commands, will be completely undone by a single U. UNDO Auto operates by inserting an UNDO BEgin at the start of each menu item, if a menu item is not already active, and an UNDO End upon exit from the menu item. • UNDO Auto is not available if the Control option has turned off or limited the UNDO feature.

8. Using the Drawing Editor • Undoing operations • Control • The UNDO Control subcommand allows the user to limit the UNDO feature or to disable it completely. It gives the prompt: • Enter an UNDO control option [All/None/One] <All>: • Enter an option or press ENTER • The options are described below. • All: Turns on the full UNDO command. • None: Turns off the U and UNDO commands entirely and discards any UNDO command information saved earlier in the editing session. An attempt to use UNDO while the None option is in effect causes AutoCAD to immediately display the prompt for the Control option: • Enter an UNDO control option [All/None/One] <All>: • One: Limits UNDO to a single operation. The Auto, Group, and Mark options are not available when None or One is in effect. The prompt shows that only a Control option or a single step of the. The prompt shows that only a Control option or a single step of the UNDO command is available when the One option is in effect. • Control / <1>:

9. Using the Drawing Editor • Undoing operations • UNDO displays the command (or system variable name) in the command line to indicate that you have stepped past the point where the command was used. • Some commands (LINE, DIM, TRIM, and EXTEND, for example) have their own UNDO subcommands. These step back one operation at a time. However, once you exit the command, U will undo the entire command. • The U command • U Reverses the most recent operation. The U command is therefore equivalent to entering undo 1. You can enter u as many times as you wish, backing up one step at a time, until the drawing is in its original state (as it was when you began the current editing session). • REDO • REDO reverses the effects of the previous UNDO or U command. REDO reverses the effects of a single UNDO or U command. REDO must immediately follow the U or UNDO command.

10. Using the Drawing Editor • Erase and Oops • You can remove an entity by using the ERASE command, and then you can redraw the entity. When you use ERASE the, the crosshair change to a pick box, to select the entity that you want to remove. In the following exercise you will erase the last line segment on your screen. ERASE command is in the Modify menu. • If you enter ERASE at the command : prompt or use the Select menu choice, ERASE lets you select many entities and then erases them at the same time. You can write OOPS to bring back the last entity group erased. In the Screen menu, ERASE command is under the MODIFY1 group.

11. Using the Drawing Editor • Getting Help • Help is almost always available online in AutoCAD. As in other Windows programs, the Help pull-down menu gives you the choices; Contents, Search for Help on, and How to use Help. Another way to use help is to issue it while using the command about which you want to learn more. After issuing the relevant command, you press F1 to get the transparent Help where a description of how to use the command is given, and the command continues. This is called context-sensitive help. Once you get more accomplished in AutoCAD you may want to consult the manual set for a thorough explanation of some of the commands. • When you access help from a Windows compatible release of AutoCAD, the Help Topics dialog box appears. Click the Contents tab to browse through topics by category. Click the Index tab to see a list of index entries: either type the word you're looking for or scroll through the list. Click the Find tab to search for words or phrases that may be contained in a Help topic.

12. Using the Drawing Editor • Command Shortcuts • If you use AutoCAD's command alias feature, keyboard command entry can be just as fast if not faster than menus. A command alias is an abbreviation that you can use instead of typing the entire command name. To execute the Circle command, for example, you can just type a C, and press Enter. Some of AutoCAD's standard abbreviations are shown in table • These command aliases are defined in the ACAD.PGP file in the Support subdirectory. Each alias uses a small amount of memory. It should be mentioned that you could edit acad.pgp, for example with Windows Notepad. • AutoCAD offers a similar keyboard shortcut for command options. You need only type the characters that are shown as uppercase in AutoCAD prompts to execute an option. For example the prompt after issuing the ZOOM command : • [All/Center/Dynamic/Extents/Previous/Scale/Window] <real time>: P • If you respond the prompt with merely a P, instead of typing the entire word Previous, the ZOOM Previous command starts.

13. Setting up an Electronic Drawing • Drawing Setup • Organizing an electronic drawing is a little different than the preparation of manual drafting. Before preparing an electronic drawing sheet, it is necessary to understand and be familiar with scale, layers and drawing entities of an electronic drawing and their difference from manual drawing. • Setting your drawing scale • Layers • Entities and Properties • Setting Up a Drawing • Setting Units • Determining Scale Factor • Calculating a Sheet Size for a Known Scale and Object Size • Setting Drawing Limits • Limit check • Working on several sheets simultaneously • Linetypes • Linetype Scale • Other Settings

14. Setting up an Electronic Drawing • Setting your drawing scale • In AutoCAD, drawing elements are stored in real world units. Your measurement units can be in fractions or decimals, in meters, millimeters, feet, inches, or any measure that you want to use. • In manual drafting, you usually create the drawing to fit a specific sheet size or scale. The text, symbols and line widths are generally about the same size from one drawing to another. In AutoCAD, however, you always draw the image at actual size (full scale) in real world units. At plot time, you can scale your full- size electronic drawings to fit the plot sheet. You must therefore plan ahead for scaling a full-size AutoCAD drawing and make settings that adjust the scale of the text, symbols, and line widths so that they plot at an appropriate size.

15. Setting up an Electronic Drawing • Layers • In manual drafting, transparent overlays may be used to separate a drawing into physical layers. In AutoCAD, virtually unlimited electronic layers are available. This gives more flexibility and control in organizing a CAD drawing than in manual drafting. • A single sheet may be pulled out to examine or modify, or you can work with all layers at once. • Any layer can contain any group of objects, which may be superimposed in space to co-exist with other objects on other layers. You should think of each layer as containing unique class of objects. You can look at all layer groups together, or you can look at any combination by specifying the layers you want to use. • You can associate any color and linetype to a layer. When you setup your AutoCAD layers, you need to determine which parts of the drawing you are going to place on each layer and what color and linetype you are going to use with each layer. You can preset each layer's color and linetype, but your layering conventions should work compatibly with those used by any consultants with whom you exchange drawings. You can make as many as, or as few layers as you need.

16. Setting up an Electronic Drawing • Layers • If your drawing is too complicated, you can turn off selected layers and work on the layers you want. Each layer has a name, a default color, and a linetype. You can work on any layer. Although editing commands such as ERASE works on any number of layers at once, you can draw on only one layer at a time. The layer you currently are using is called the current layer. When you start a new drawing, layer 0 is the current layer, which is the default layer from the ACAD.DWT / ACADISO.DWT scratch drawings. • The Layer Properties Manager dialog box contains every available tool for defining and setting up new layers. You can access this dialog box from the Format pull-down menu by selecting the Layer… option; by entering DDLMODES or LAYER command at the Command: prompt, or by clicking on the LAYER button from the object properties toolbar.

17. Setting up an Electronic Drawing • Layers • Once created, you can set the current layer by choosing from the layer drop-down list in the object properties tool bar area. • Keeping a good layer organisation is very important for efficient work. Keep entity colours BYLAYER and one linetype per layer whenever possible. For example, keep one layer for dimensioning only, one layer for construction lines (help lines), one layer for hatching and so on. • Layers can be used to draw efficiently by reducing duplicate work. For example, architects commonly use the same floor plan for several different applications, one for dimensions, one for furniture arrangement, one for electrical details, and so forth. The same basic plan is used for all these applications by turning on the needed layers and turning off others. A disadvantage of this method is that the drawing file will increase greatly in size. • NOTE: AutoCAD add-on programs may structure layers specifically for the program functionality. A proposal exists for an international standard for structuring layers in computer aided Building Design, the ISO DIS 13567, which may become an ISO standard similar to linewidths and paper sizes. This will make it easier for different parties to exchange drawings.

18. Setting up an Electronic Drawing • Linetypes • AutoCAD linetypes, continuos, dashed, dot and so on, are stored in linetype library files with the extension .LIN. • By default, only the linetype CONTINUOUS is available. To be able to SET different linetypes you must first load them from a library file. • You set, load, and list linetypes with the LINETYPE Manager Dialog Box. • Command: LINETYPE  (Opens the Linetype Manager Dialog Box) • If you have not created your own library file, you can choose only ACAD.LIN / ACADISO.LIN • You can create a new linetype and store it in a specified library file. We will not cover custom linetypes in CE-101. Consult the AutoCAD Customization Manual. • The Loads option loads selected linetypes from a specified library file.The Current option sets the current linetype used for newly drawn entities. However, it is better to organize linetypes as much as possible by the use of layers. • In AutoCAD linetypes can consist of repeating patterns of dashes, dots blank spaces ,shapes and letters as well. AutoCAD 13 linetypes that contain shapes and letters are contained in a second library file ltypeshp.lin.

19. Setting up an Electronic Drawing • Linetype Scale • The length of dashes in AutoCAD linetypes is in drawing units. Since drawing units mean millimetres in some drawing and kilometres (or whatever) in others, a method is provided for adjusting the linetypes to a meaningful scale for your drawing with the system variable LTSCALE. In civil engineering the drawing unit is normally meters. The default value of LTSCALE is 1.0. • The LTSCALE command governs the global scale factor for dash lengths, ie. It affects all non-continuous lines in your drawing. • Adjust your LTSCALE according to your drawing scale (plotting scale) factor and limits. Guideline values for LTSCALE could be: • In AutoCAD you can set a linetype scale for individual entities. The entity-specific linetype scale will be in relation to the global scale, not replace it.

20. Setting up an Electronic Drawing • Setting Units • You can choose your system of units by using the Units option from the Format pull-down menu or by writing UNITS at the command promy. Both Units selection from the Format pull-down menu and writing DDUNITS or UNITS at the Command: Promt displays the Drawing Units dialog box which gives you control over the unit options. Setting up units sets up the input format for entering distances and angles from the keyboard, and output format that AutoCAD uses when displaying and dimensioning distances and angles. • In Turkey, SI (Systeme International d’Unites) units are used, ie. Length in meters and decimal fractions. We will only be using SI in CE-101, but AutoCAD accepts other notations such as scientific, fractional and the special Engineering /Architectural systems which are used in the United States. • Normal angle measurement in engineering is in decimal degrees. Other notations available in AutoCAD are radians, grads (surveying) and degrees/minutes/seconds, which should not be confused with decimal degrees, for example : • 30.125° = 30°7'30" • You can also change the angle direction which controls the point from which AutoCAD measures angles and the direction in which they are measured. The default is 0 degrees on the right side of the figure, measured counterclockwise. To specify a new angle direction choose Direction from the drawing units dialog box.

21. Setting up an Electronic Drawing • Determining Scale Factor • First, you must determine a drawing scale factor, and then you use it to calculate the • sheet size • text heights (see chapter 6 for Text) • symbol size • linetype scale • The limits setting is the AutoCAD equivalent of sheet size. You set the drawing's limits during the initial drawing setup. Linewidth is determined when you are setting up for plotting. AutoCAD line entities have zero width. Standard line widths are: 0.7mm, 0.5mm, 0.35mm, 0.25mm, 0.15mm. On screen all lines have the same width, but different colours. • Sheet size is calculated in the same way as in manual drafting, except that you use the resulting scale ratio to scale up the sheet size to fit around the full scale size of your drawing. Then when you plot the drawing, you scale everything back down by the same factor. In Europe paper sheet sizes are predominantly according to DIN (Deutsche Institut für Normung): • A4: 297 x 210 mm • A3: 420 x 297 mm • A2: 594 x 420 mm • A1: 841 x 594 mm • A0: 1189 x 841 mm • For mapping purposes or large civil engineering projects, such as a road construction, larger sizes are used. If you are working on a floor plan that is 31.5 meters by 20 meters, you may want the drawing to be scaled at 1m : 100m. What is your scale factor and what size electronic sheet you are going to use? The size of your electronic sheet is set by the limits that you choose. The limits are determined by the X,Y values of the lower left and upper right corners of your electronic sheet.

22. Setting up an Electronic Drawing • Calculating a Sheet Size for a Known Scale and Object Size • You set the limits by multiplying the sheet size by your scale factor; • Size of floor plan :6.3 x 4.0 meters • Scale :1: 20 • Scale factor :20 • Now test a 21 by 29.7 cm sheet (A4) : • 21 x 20 = 420cm or 4.20 m • 29.7 x 20= 594 cm or 5.94 m • This sheet size is not sufficient, because the 6.3 x 4.0 meters drawing does not fit on the sheet. • Now test a 29.7 by 42cm sheet (A3) : • 29.7 x 20 = 594 cm or 5.94 m • 42 x 20 = 840 cm or 8.4 m • This should work with plenty of room for dimensions, notes and a border. • In the previous example, you determined your limits by the number of units that fit across a standard sheet. If you have to fit the drawing to a predetermined sheet size, start with that size and the size of what you are drawing, and then calculate the scale factor from them : • 42 x 29.7 cm sheet and 6.3 x 4.0 m object: • 6.3 m equals 630 cm, 42 cm : 630 cm (ratio of sheet size to object size) equals a ratio of 1: 15 • To draw a borderline, a title block, text and to show dimensions we need an extra space around the sheet so we should increase the scale factor. If we accept a scale factor of 20 : • 42 cm x 20 = 840 cm or 8.4 m • 29.7 cm x 20 = 594 cm or 5.94 m • These limits of 840 cm by 594 cm should work. • Your limits do not actually limit the size of your drawing. Think of AutoCAD 's limits as an electronic fence. If you draw outside your boundary AutoCAD warns you. If necessary, you can expand the sheet by resetting the limits.

23. Setting up an Electronic Drawing • Setting Drawing Limits • After you establish your drawing's units, use the Drawing Limits option from the Format pull-down menu to set sheet boundaries for your drawing. By default, AutoCAD specifies the lower left boundary of your intended drawing area is X=0 and Y=0. You can enter a new lower left corner by assigning new X,Y coordinates. Then, you can accept the upper right corner default values or assign new X,Y coordinates. You can also issue the LIMITS command by entering LIMITS at the Command: prompt. AutoCAD does not insert a border around the drawing area when you set the limits. You can solve this problem by setting a drawing grid. A grid is also useful for estimating coordinate values and distances. • File  New  Save as  SET (Begins a new drawing named SET.) • Format  Units (Drawing Units dialog box) • Choose the Decimal radio button in the Units area. • Format  Drawing Limits (Starts the LIMITS command.) • Specify lower left corner or [ON/OFF] <0.0000,0.0000>: Press Enter (Accepts the default location for the lower left corner) • Specify upper right corner <420.0000,297.0000>: 840,594 (Sets the limits for the upper right corner) • Tools  Drafting Settings... (Displays the Drafting Settings dialog box) • Snap and Grid  Grid On check box (Turns on the Grid) • Enter 10 in the Grid X Spacing box (Sets the grid spacing to 10 cm) • Snap On check box  Enter 10 in the Snap X Spacing box • View  Zoom  AllZooms (limits and the grid cover the drawing area) • Press Enter (Repeats the ZOOM command) • Choose File, then SaveSaves the drawing as SET.DWG. • The area covered by the grid is the defined limits, representing an 42.0 by 29.7 cm plotting sheet at 1/20 cm = 1 cm scale. If you draw outside the grid, you are drawing outside the area that represents the intended plot area.

24. Setting up an Electronic Drawing • Limit check • LIMITS command has an ON/OFF prompt, for limits checking. When you turn on limits checking, AutoCAD does not allow you to draw outside the limits. • Settings  Drawing Limits (Starts the LIMITS command) • Command: '_limitsReset Model space limits:Specify lower left corner or [ON/OFF] <0.00,0.00>: • Enter ON (Turns on limits checking) • While limits checking is enabled, AutoCAD rejects attempts to enter points outside the drawing limits, although an entity, such as a circle, might start within the limits and extend outside them. The LIMITS command affects the LIMCHECK (warning or not), LIMMIN (lower-left drawing limits for the current space, expressed in world coordinates), and LIMMAX (upper right limit) system variables in the current space.

25. Drawing Accurately • Grid (F7) and Snap (F9) • Object Snaps • Coordinates To be continued next week