Computer Aided Engineering Drawing Basic Concepts of Auto

Computer Aided Engineering Drawing Basic Concepts of Auto. CAD Chapter No 2 Sir Syed University of Engineering & Technology Computer Engineering Department University Road, Karachi-75300, PAKISTAN

CAED - Chapter No 2 Basic Concept of Auto. CAD Text Book n Text Book: Mastering AUTOCAD 14 By George Omura n Course Outline is available at CAED course website. 2

CAED - Chapter No 2 Basic Concept of Auto. CAD Chapter Outline n n n n n Coordinate System Limit Command Unit Command GRID and SNAP Command ORTHO Command OSNAP Command ZOOM Command REDRAW and REGEN Command PAN Command HIGHLIGHT Command 3

CAED - Chapter No 2 Basic Concept of Auto. CAD Co-ordinate System in Auto. CAD’s drawing environment is based on the Cartesian coordinate system n The horizontal axis is called the X-axis and the vertical axis is called the Y-axis. The plane that contains these axes is called the X-Y Plane. n The X-axis and The Y-axis intersect at a single point, called the origin. Equidistant points, called the coordinates are placed along these axes. 4

CAED - Chapter No 2 Basic Concept of Auto. CAD 3 Ways to Enter Values n Absolute System n Relative System n Polar System 5

CAED - Chapter No 2 Basic Concept of Auto. CAD Co-ordinate System in Auto. CAD n Absolute System: X, Y n Absolute System represents the absolute real values of the drawing limits. n For example 3, 3 to 8, 3 will draw a line from the position vector of 3, 3 to the position vector of 8, 3. n You can specify a point by typing its X, Y and Z values separated by the commas. n Example: Command: line From point: 3. 5, 4. 5, 5. 5 6

CAED - Chapter No 2 Basic Concept of Auto. CAD Co-ordinate System in Auto. CAD n Relative System: @delta X, delta Y n Relative System represents the relative position of X and Y coordinates of the new points compared to the previous points. n For example line from 3, 3 to @5, 0 will draw a line from the position vector of 3, 3 to the position that is 5 units away from the previous points in the positive X -axis direction. 7

CAED - Chapter No 2 Basic Concept of Auto. CAD Co-ordinate System in Auto. CAD n Relative System: @delta X, delta Y n You can specify a point as an offset from the last point you entered, simply type an @ before the rest of the specification. n For instance last point = 10, 6, 4 n Example: @2. 5, 5 8

CAED - Chapter No 2 Basic Concept of Auto. CAD Co-ordinate System in Auto. CAD n Polar System: @dist < Angle n Similar to the relative addressing, this system makes use of the distance and the direction angle of the new point away from the previous point. n For example, line from 3, 3 to @5 < 0; will draw a line from the position vector of 3, 3 to the position that is 5 units away from the previous points in the zero degree direction. 9

CAED - Chapter No 2 Basic Concept of Auto. CAD Co-ordinate System in Auto. CAD n Polar System: @dist < Angle n You can specify a point by entering its distance from the current UCS origin and its angle in the XY plane separated by the sign <. 90 n Example: @5 < 45 180 0 n Example: @10 < 180 270 10

CAED - Chapter No 2 Basic Concept of Auto. CAD LIMITS Command n Before beginning a new drawing, it is very important that you define the drawing boundaries for the current drawing. n The LIMITS command lets you change the upper and lower limits of the drawing area while working on a drawing, and to turn limits checking on or off. n The current drawing area has a length of 12 units and a breadth of 9 units, by default. 11

CAED - Chapter No 2 Basic Concept of Auto. CAD LIMITS Command n Format: LIMITS ON/OFF/ <Lower left corner> <current>: Upper right corner<12. 0000, 9. 0000>: n Options n ON n OFF Enables limits checking, retaining the current values of the limits themselves. While limits checking are enabled, Auto. CAD 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). Also governs the limits of the visible grid. Disables limits checking, but remembers the values of the limits for the next time the check is enabled. 12

CAED - Chapter No 2 Basic Concept of Auto. CAD UNITS Command n The UNITS command governs the display and input formats for coordinates, distances, and angles. The UNITS command doesn't compromise the accuracy of calculations, only the way that numbers are displayed and input to a drawing. n Format: UNITS n When you enter the UNITS command, Auto. CAD prompts you to make the following selections: 13

CAED - Chapter No 2 Basic Concept of Auto. CAD UNITS Command n Display/input formats for coordinates and distances: n n n Scientific Decimal Engineering Architectural Fractional 1. 55 E+01 15. 50 1'-3. 50" 1'-3 1/2" 15 ½ (15. 5 drawing units) " " 14

CAED - Chapter No 2 Basic Concept of Auto. CAD DDRMODES -- Drawing Aids Dialogue Box n The DDRMODES command lets you control the settings of various drawing aids, such as Snap and Grid by using dialogue boxes. Dialogue boxes work only with certain display drivers. n Format: DDRMODES n When you issue the DDRMODES command, Auto. CAD displays the Drawing Aids dialogue box, allowing you to control on-screen drawing aids. n It subsumes all of the functions of the ORTHO, FILL (Solid Fill), QTEXT (Quick text), BLIPMODE (Blips), HIGHLIGHT, SNAP, GRID, and ISOPLANE commands. 15

CAED - Chapter No 2 Basic Concept of Auto. CAD DDRMODES -- Drawing Aids Dialogue Box n Options n Snap Spacing n Sets alignment spacing. n ON OFF Aspect Rotate n Style n n n Aligns designated points. Does not align designated points. Sets different X/Y snap resolution. Rotates snap grid by specified angle, and sets a specified base point for the grid. Sets Snap style to either Isometric or Standard. 16

CAED - Chapter No 2 Basic Concept of Auto. CAD GRID Command n The GRID command controls the display of a grid of alignment dots to help you place objects in drawings. n n Format: GRID Grid spacing (X) or ON/OFF/Snap/Aspect <current>: n Note: You can also turn GRID on and off using the F 7 key or CTRL+G. 17

CAED - Chapter No 2 Basic Concept of Auto. CAD GRID Command n Options n n Grid Spacing (X) n A simple number sets grid spacing in drawing units. A number followed by "X" (e. g. , "2 X") sets the grid spacing to a multiple of the current snap resolution. A value of zero locks the grid spacing to the current snap resolution. ON n Turns grid on with previous spacing. OFF n Turns grid off. Aspect n Permits a grid with different horizontal and vertical spacing. 18

CAED - Chapter No 2 Basic Concept of Auto. CAD SNAP Command n The SNAP command lets you control the snap resolution, the spacing of an imaginary grid of dots with which newly designated points must align. You can alter the resolution or turn it off entirely for freestyle drawing. n Format: SNAP n Snap spacing or ON/OFF/Aspect/Rotate/Style <current>: n Note: Snap can be turned on and off with the F 9 key or CTRL+B 19

CAED - Chapter No 2 Basic Concept of Auto. CAD ORTHO Command n The ORTHO command lets you control orthogonal drawing mode. n When orthogonal mode, also known as "ortho" mode, is set to ON, movement within the drawing is constrained to the vertical and horizontal axes, as these are defined in the current Snap grid. n n Format: ORTHO OFF/ON <current>: 20

CAED - Chapter No 2 Basic Concept of Auto. CAD ORTHO Command n Options n ON n OFF Turns orthogonal mode on. Turns orthogonal mode off. n Note: n When the Snap grid is rotated, Ortho mode rotates accordingly. Also, if the isometric snap style is in effect, Ortho mode is applied to the axis pair associated with the current isometric plane. n Note: ORTHO can be turned on and off with the F 8 key or Ctrl + O. 21

CAED - Chapter No 2 Basic Concept of Auto. CAD OSNAP Command n Object Snap defines the way in which you can snap to those drawings that are already completed. n The OSNAP command is used to set "running" object snap modes from the Command line. (DDOSNAP sets them using a dialogue box). n Object snap lets you designate points that are related to objects already in your drawing. n n Format: OSNAP Object snap modes: 22

CAED - Chapter No 2 Basic Concept of Auto. CAD OSNAP Command n Options n CENter ENDpoint n INSertion n INTersection n MIDpoint n NEArest PERpendicular TANgent n n n Center of Arc or Circle Closest endpoint of Line/Arc or closest corner of Trace/Solid/3 D Face Insertion point of Text/Block/Shape/Attribute Intersection of Lines/Arcs/Circles or corner of Trace/Solid/3 D Face Midpoint of Line/Arc or midpoint of an edge of Trace/Solid/3 D Face Nearest point on Line/Arc/Circle/Point Perpendicular to Line/Arc/Circle Tangent to Arc or Circle 23

CAED - Chapter No 2 Basic Concept of Auto. CAD ZOOM Command n The ZOOM command magnifies or shrinks the drawing on the display screen. n Format: ZOOM n All/Center/Dynamic/Extents/Left/Previous/Vmax/ Window/<Scale(X/XP)>: 24

CAED - Chapter No 2 Basic Concept of Auto. CAD ZOOM Command n Options n All Center n Dynamic n Extents n Vmax n Window n Displays entire drawing (all visible layers). Specifies center point and new display magnification. Permits you to pan a box representing the viewing screen around the entire generated portion of the drawing and enlarge or shrink it in a dynamic, graphic manner. Displays current drawing content as large as possible. Zooms out as far as possible without forcing a regeneration. Designates rectangular area to be drawn as large as possible. 25

CAED - Chapter No 2 Basic Concept of Auto. CAD BLIPMODE Command n The BLIPMODE command controls the generation of marker "blips" -- the small temporary marks drawn whenever you designate a point. n n Format: BLIPMODE ON/OFF <current>: n Command Options n n ON OFF Blips are drawn. Blips are suppressed. 26

CAED - Chapter No 2 Basic Concept of Auto. CAD REDRAW Command n The REDRAW command redraws the current viewport, causing it to appear opaque over viewport behind it. REDRAW also eliminates any point entry blips from the display. n Format: REDRAW n You can use the REDRAWALL command to redraw all active viewports. Both commands can be used Transparently as 'REDRAW and 'REDRAWALL. n Viewport is the bounded area that displays some portion of the drawing model space. 27

CAED - Chapter No 2 Basic Concept of Auto. CAD REDRAWALL Command n The REDRAWALL command redraws all viewports, eliminating all point entry blips from each viewport. n Format: REDRAWALL n The REDRAW command can be used to redraw the current viewport only, causing it to appear opaque over viewports behind it. n Both commands can be used transparently as 'REDRAW and 'REDRAWALL. 28

CAED - Chapter No 2 Basic Concept of Auto. CAD REGEN Command n The REGEN command regenerates the drawing in the current viewport by recalculating all the entities in the drawing database, and redrawing the screen. n Format: REGEN n Regeneration occurs automatically when you change the display of your drawing with some ZOOM or PAN operations. It also occurs in the HIDE and SHADE commands. n The REGENALL and REGENAUTO commands have further control over regenerations. 29

CAED - Chapter No 2 Basic Concept of Auto. CAD REGENAUTO Command n Some commands can change many entities at once. The drawing must be regenerated to reflect such a change, so some commands perform this regeneration automatically. n The REGENAUTO command lets you control whether automatic regenerations are performed on a drawing. n Format: REGENAUTO 30

CAED - Chapter No 2 Basic Concept of Auto. CAD REGENAUTO Command n ON/OFF <current>: n If REGENAUTO is set to OFF, and a ZOOM or PAN needs to regenerate the drawing, Auto. CAD prompts: n About to regen, proceed? <Y> n If you respond with N, the PAN or ZOOM is aborted. This prompt does not appear if input is coming from a menu item or a script. 31

CAED - Chapter No 2 Basic Concept of Auto. CAD PAN Command n The PAN command lets you move the display window in any direction, without changing its magnification. n It has the same effect as using the scroll bars. This lets you see details that are currently off screen. n You can specify a relative movement, as in: n Format: PAN n Displacement: Enter relative coordinates. n Second point: Press. 32

CAED - Chapter No 2 Basic Concept of Auto. CAD PAN Command n Or you can designate two points to specify the displacement you want. n Format: PAN n Displacement: Indicate a point. n Second point: Indicate a point. 33

CAED - Chapter No 2 Basic Concept of Auto. CAD HIGHLIGHT Command n HIGHLIGHT is a system variable that determines whether entities will be displayed as dashed objects when object selection is in progress. The value stored is an integer. n Options n 0 n 1 Entities will not be highlighted during object selection. Entities will be highlighted during object selection. 34

CAED - Chapter No 2 Basic Concept of Auto. CAD Getting Out of Trouble from Auto. CAD n Backspace < > Whenever you make a typing error you can use the backspace key to delete up to the error. n Cancel < Ctrl + C > After executing a command, if you have decided not to continue with that command then presses the key: Ctrl+C for canceling a command. Alternatively, you can also click at the Auto. CAD found at the top right corner. 35

CAED - Chapter No 2 Basic Concept of Auto. CAD Getting Out of Trouble from Auto. CAD n Escape < ESC > If you want to quickly exit from a dialog box without making any changes, then you can press the ESC key. n Undo < U > If you have accidentally change something in the drawing and you want to reverse back the change, then you can press the U key at the command prompt. n Redo If you have accidentally undo one too many commands, you can redo (undo the undo) the last commands by entering the command REDO. Redo restores only one command. 36