Lesson (Week) #2,
EGR-110-40, Burgener, Monday August 28, 2000
Note: The bookstore has the optional Instant Reference book (by George Omura, ISBN: 0-7821-2497-6) in stock, for $20. I suggest you buy one, UNLESS you already have a a book for AutoCAD 2000, AND are already somewhat familiar with AutoCAD.
Turn in: The pages D-1 and D-2 handed out last week, at the start of class today.
Topics covered in class:
I walked through problems #5 and #11 on the page 27 homework on the board. Remember, all of page 27 is due next class (two weeks from today). We'll skip Monday September 4th, for Labor Day weekend.
AutoCAD Commands and Concepts:
NOTE: "irp" below means the page from your optional Instant Reference book.
Review of last week's AutoCAD commands:
Precidence of lines: Let's table this topic for a while. I need to check the ANSI specs for clearification. Page 100 section 5-4, 2nd paragraph says "... if either a centerline or a solid line is coincident, both would take precidence over a hidden line." However, other textbooks (Giesecke's Engineering Graphics, 2nd ed, page 148) say "A hidden line always takes precidence over a centerline."
"KEY"- The word "Key" means a letter or character on your keyboard.
"Button"- The word "Button" implies a virtual button on your screen, that you can click with your mouse.
Remember to check that "Command:" is on the Command area (bottom) of your screen, before beginning any drawing or editing operation. If you don't see the word "Command:", then hit the ESC key once or twice. Strange things happen if you try to begin a new operation, while an older operation is still being worked.
If blue squares appear on your lines, hit the Esc key twice to get rid of them. These "Grips" are useful in more advanced AutoCAD lessons, but are an annoyance this early.
Status bar buttons: The far right button at the bottom of your screen should always show "MODEL". The other 7 buttons on the status bar should be OFF for now, except that you can toggle the ORTHO button off and on all you like, to make straight vertical and horizontal lines.
LINE, L irp166 After the first point in using the LINE command, you can type in coordinates (Absolute, Relative, or Polar) OR you can simply select the locations (points) on your screen with your mouse. When you're finished drawing your single or zig-zag line, hit the Enter key to complete the command and return to the "Command:" prompt at the bottom of your screen.
Note: If you make a mistake while drawing a zig-zag line, click the UNDO button on the Standard Toolbar, or hit the U key and the Enter key to back up one step (vertex) of the line you're making.
Real Time PAN irp210
Real Time ZOOM irp 371 top
ZOOM All irp371 This shows all there is to see of your drawing, even the space taken up by the grid dots, even if the GRID is turned off (as I'd prefer it for now), on your status bar.
ORTHO irp205 Like the old T-square from manual drafting, ORTHO limits your lines to be either vertical or horizontal. You can toggle ORTHO on and off while drawing zig-zag lines. Suggest use the ORTHO button on the status bar to toggle it on and off.
Direct Distance irp231
Very handy when ORTHO is on, for drawing lines of a known length.
ERASE, E irp 114 Select what you want to erase by clicking each line with your mouse. When you're finished selecting things, hit the Enter key to tell AutoCAD you're ready to erase them all. Until you hit Enter, AutoCAD keeps waiting for you to select more items.
Object Snaps irp99 Please keep the OSNAP button toggled OFF on your status bar. Use an individual Object Snap each time you want to "home in" on a specific location, like the MIDpoint of a line, the CENter of a circle, or the ENDpoint of a line.
New AutoCAD Commands and Concepts:
Absolute Coordinates p24, irp231 Each time you're asked to specify a point (like when making lines), you can type in the X and Y values.
Relative Coordinates p24, irp 232 With relative coordinates, you type in the CHANGE of X and Y location, with respect to the last point (location) you used. Begin typing with "@" (Shift-2), then the X change, then a comma, then the Y change in location.
(relative) Polar Coordinates p26, irp232 These are similar to the Relative Coordinates above, but they use a distance and the angle counterclockwise from straight right, instead of the change in X and Y locations. Begin these with the @ sign, then the distance, then type the < sign, then the angle counterclockwise from straight to the right (3:00 on your screen). Be aware you can type in a negative distance or angle. This is handy for lines straight down, for example. You can type @6<-90 instead of @6<270.
CIRCLE, C irp43 After clicking the CIRCLE icon, or typing C, you need to decide which way you want to make the circle. You can define a circle by 3 points, center and diameter, center and radius, etc etc. Hit the key for the first letter of the option you want to use.
After learning the CIRCLE command, you'll soon want to learn the QUAdrant and TANgent Osnaps. QUAdrant "homes in" on the 4 "corners" of a circle (3:00, 6:00, 9:00 and 12:00). TANgent connects a line to the edge of the circle, like fan belts that go around a pair of pulleys. You must hit the final Enter to see the lines form.
ARC, A irp9 Like the CIRCLE command above, the ARC command involves options that allow you to decide how to define the arc.
REGEN, RE irp250 Once we begin making circles and arcs with AutoCAD, you'll notice the curved lines sometimes look like a series of short lines. A circle sometimes appears to be an octagon, when you ZOOM in very close. The REGEN command forces the computer to regenerate the display to show the roundness of the arc or circle. If AutoCAD showed the complete roundness all the time, instead of aproximating the curves with short lines, the display of your drawing would take more time. We'll later learn how to avoid typing RE as often.
Practice AutoCAD exercises for this week:
Page 38 problem B, using Relative Coordinates
Page 40, FIG. 2-6-H, using relative Polar Coordinates
. . Note: Change the length of JA from .531 to 1.53. This is still a few thousandths off from perfect, though.
Page 129 FIG. 5-6-B number 4 "Top" view, using the CIRCLE command.
. . Note: The QUAdrant Osnap might be helpful, depending how you draw it. Plan to draw some extra (construction) lines, that you'll later erase.
Page 165 FIG. 6-6-B (B) and (C) to practice the ARC command
Page 157 FIG. 6-1-A number 2.
. . Note: Use the TANgent Osnap for all the "fan belt" lines.
Page 175 FIG. 7-1-7
. . Note: The figure in the book is grossly out of scale. Also, assume the overall length (left to right) is 5.
Page 136 FIG. 5-9-A for more CIRCLE practice.
. . Note: None of these above practice assignments will be turned in. Depending on the time, we'll rush through some and maybe skip a few.
Due next week: Page 27 "complete the views" puzzles. Remember to show all necessary visible, hidden, and centerlines. Be aware some have more than one correct answer. You can expect to see a few of these puzzles (or new ones) on upcoming quizzes, the midterm, and the final exam.
Heads up for next week: (later) We'll probably learn about Layers, colors, and linetypes.