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Computer Aided Engineering Drawing 1
FIRST SEMESTER
COMPUTER AIDED ENGINEERING DRAWING
COMPUTER SIMULATION LAB
DEPARTMENT OF ELECTRICAL ENGINEERING
Prepared By: Checked By: Approved By:
Najeeb Saif Engr. M.Nasim Khan Dr.Noman Jafri
Lecturer Electrical, Senior Lab Engineer Electrical, Dean,
FUUAST-Islamabad FUUAST-Islamabad FUUAST-Islamabad
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Name: ____________________________________________
Registration No: ____________________________________
Roll No: ___________________________________________
Semester: _________________________________________
Batch: ____________________________________________
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Computer Aided Engineering Drawing 3
CCCOOONNNTTTEEENNNTTTSSS
Exp No List of Experiments
1 Introduction to AutoCAD Environment
2 Starting drawing in AutoCAD (some draw and modify
commands)
3 Advance 2-D drawing
4 Continuation to Lab # 3
5 Plotting drawing in AutoCAD
6 Concepts and techniques used to build 3-D Models I
7 Concepts and techniques used to build 3-D Models II
8 Concepts and techniques used to build 3-D Models III
9 Isometric Drawing I
10 Isometric Drawing - II
11 Isometric Drawing - III
12 Isometric Drawing -IV
13 Getting Started with Microsoft Visio
14 Block diagrams and logic diagrams
15 Schematic Diagrams-I
16 Schematic Diagrams-II
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EXPERIMENT NO 01
Introduction to AutoCAD Environment
Starting AutoCAD
Start AutoCAD by clicking on the Windows Start button (bottom
left), then move the mouse to Programs then CAD and Modeling then
"AutoCAD Architectural Desktop 2" and click on AutoCAD
Architectural Desktop 2. A dialog giving various startup options
will be displayed. Select the second option: "Start from Scratch"
and click OK.
Once you have loaded AutoCAD, move the mouse around until you
see a crosshair cursor. The AutoCAD window has a number of
important features:
Figure 1 AutoCAD screen.
1. The standard Windows drop-down menus. 2. The standard Windows
toolbar below the menus, it includes: File-New, File-Open,
File-Save,
Print and "Find and Replace"(!!).
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Computer Aided Engineering Drawing 5
3. In addition to the standard toolbar there will be a number of
AutoCAD specific toolbars: Object Properties, Draw and Modify
(there may be others...?).
4. The graphics areas - that's the area where you draw - note
the scroll bars and the axis label. 5. View Tabs - these 'tabs'
give access to different view of the current drawing. The "model"
tab
should be selected at present. 6. The command area - this small
window (by default) has space for three lines of text - this is
where you type commands. 7. The status area, at the bottom of
the AutoCAD window, this includes the current cursor
position.
NOTE: Despite command line interfaces being considered totally
archaic the command area in AutoCAD is absolutely vital! One of the
key things I'm trying to "get you to do" in these tutorials is to
watch the command area! Using AutoCAD is like a conversation and
AutoCAD's half of the conversation comes from the text in the
command area...
Command Entry
Typically there are three ways of giving a command:
1. Type the command using the keyboard - the command is
displayed in the command area.
When I want you to type a command in the command area the
AutoCAD command will be written like:
Type: QSAVE
(This means: type the text (qsave) and then press the Enter key
or the space-bar)
(Not all commands are on the Menus and/or toolbars)
2. Select the command from a menu.
When I want you to select a command from a menu, it will look
like:
Select File Save (This means: click on the 'File' menu and then
'Save' which is one of the items on the 'File' menu).
3. Select the command's icon from a toolbar.
When I want you to pick a command from a toolbar, I'll
write:
Select Save
(AutoCAD also supports common shortcuts like Ctrl-S for
Save)
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Computer Aided Engineering Drawing 6
Draw a Rectangle
Select Rectangle (or type rectang ), then type:
15, 15 415,315 these are absolute Cartesian coordinates
(The text typed is displayed in the command area at the bottom
of AutoCAD's window)
AutoCAD must have drawn a rectangle, which fits comfortably in
the AutoCAD graphics area. If you can't see the rectangle, type z
[space] a [space] (zoom all) - this instructs AutoCAD to redraw the
view, "zooming out" to show all the graphics on the drawing.
Saving a Drawing
Select the Save icon from the standard toolbar. The drawing has
not been saved before, so AutoCAD will display the SAVE AS dialog
box, select the appropriate Drive and Directory (for example:
C:\local\abc), type the drawing name (for example Lab1), and then
select "OK".
(Note that if you type SAVE , you actually get "Save As") (The
quickest way to save is to press Ctrl-S - this is the same as
"qsave)
Draw some Lines
We will now draw some more graphics and then save and exit
AutoCAD. Type LINE Move the crosshair to near the bottom-left of
the rectangle and click the left mouse button,
then move the crosshair to the top-right of the rectangle and
again click the left mouse button.
Press to terminate the command, and then press again to re-start
the command. Draw a line from the top-left to the bottom-right of
the rectangle, and then press to end the
command. Now type:
QUIT You will be prompted to save the changes you've made -
click OK.
(This will save the drawing and exit AutoCAD - don't PANIC)
Starting AutoCAD with an Existing Drawing
To load a drawing, either click on the "Your Account" icon or
start Windows Explorer and select the appropriate Drive and
Directory. Once Explorer is showing the correct directory then
double-click on your drawing.
If you can't find your drawing (in Windows Explorer) then press
F5 (function key 5), this tells Explorer
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to update the directory display; if you still can't find your
drawing then perhaps you saved the drawing in some other directory
- load AutoCAD and then select the File menu, at the bottom of the
File menu is a list of recently opened drawings, select your
drawing from the list.
Coordinate Systems
When specifying positions you can use Cartesian or Polar
Coordinates. Cartesian coordinates are simply a X value, a comma,
and a Y value, for example: 100,100. Polar coordinates are a
Distance followed by a < symbol and an angle, for example:
10
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The object snap modes can either be typed or they can be
selected from the standard toolbar or from the snap toolbar:
Figure 2 Object Snap Toolbar
(To display the "Drafting Settings" dialog, click on the
"horse-shoe" shaped icon on the end of the Object Snap Toolbar)
Draw an Arc
Select Arc (or type ARC ), then select the midpoint snap mode
(or type: MID ) and select the left side of the bottom of the
"diamond" polyline you drew before. Then use the midpoint snap to
enter points on the right side at the bottom and then the top of
the polyline (see figure 2).
Figure 3: Lab1 drawing
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Computer Aided Engineering Drawing 9
EXPERIMENT NO 02
Starting drawing in AutoCAD (some draw and modify commands)
Starting AutoCAD
Start AutoCAD, and then move the cursor to the bottom left of
the screen, you will note the coordinates (on the status line) go
down to near 0,0. In the version I am using the drawing limits are
set to the size (in millimeters) of an A3 sheet of paper
(420,297).
Setting the Limits and Units
It is normal when using AutoCAD to draw objects full size, so
it's usually necessary to reset the drawing limits to (about) the
size of the object being drawn (or in the case of a building the
building's site). Type:
limits This sets the drawing "size" to 50 x 50 meters.
0,0 50000,50000
(Alternatively, select Format - Drawing Limits and then type the
numbers shown)
Next we need to get rid of the 4 decimal points! Select "Format
- Units...", AutoCAD will display the "Drawing Units" dialog. Make
sure Decimal is selected in the Units section and Decimal Degrees
in the Angles section, then in Unit's Precision, click on the down
arrow beside "0.0000" and select "0", and finally select "OK". This
sets the "model space" dimensions. To reset the drawing view to the
whole of the (empty) drawing, select the zoom-all icon, which is
hiding under the zoom-window icon (on the standard toolbar) - hold
the button down and then rest of the zoom toolbar is displayed (or
type: Z [space] A [space] ).
(Zoom All , Zoom Window ) (Z is the alias (shortcut) for ZOOM.
Remember that [space] is the same as .)
Move the cursor around now and note that the coordinates are now
bigger numbers.
Let the Drawing Begin!!
Firstly draw a rectangle from 0,0 to 50000,50000.
(This shows us the "drawing area")
Then draw a circle, centered at 30000,24000 with a 6000 radius.
Select circle or type:
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C , then type: 30000,24000 the circle centre 6000 the circle
radius
(Circle , "C" is the alias for CIRCLE)
Next you will draw another circle, with the same centre, but
with a 9500 radius. Press: to "recall" the last command. Select the
centre snap mode (or type: CEN ), then pick the first circle (NOT
the centre of the circle), then type:
9500 the circle radius
(Centre snap , to get AutoCAD to display the Object Snap Modes
toolbar, select "Toolbars" from the "View" menu and then select
"Object Snap)
Next draw a rectangle from the centre of the circles to
39500,33500. Once you have done that draw another rectangle to the
right of the last, start at 39500,24000 and make the rectangle
1500x9500. (Hint: use a relative coordinate @1500,9500)
Now you will draw an arc on the end of the last rectangle (see
figure 1). Select Draw - Arc - Start-Center-End, then select the
Endpoint snap mode (or type: END ) and select the bottom-right of
the last rectangle. For the centre point of the Arc, select the
Midpoint Snap Mode (or type: MID ) and select the middle of the
right edge of the last rectangle. For the end of the Arc, select
the Endpoint Snap Mode and select the top-right of the
rectangle.
(You might find the following section easier if you turn object
snapping ON) Endpoint Snap Midpoint Snap
Figure 1 showing the location of the ARC
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Copy & Rotate . . .
Now we want to copy & rotate the two rectangles and the arc
(3 times), AutoCAD provides the array command to achieve this.
Select Modify - Array, AutoCAD will prompt for the objects to be
selected: click below and to the left of the bottom-left corner of
the left rectangle and then move the mouse until the selection
rectangle encloses the two rectangles and the arc - then click the
mouse button (3 objects should be selected). Then press to end the
selection process.
(The array command is used to copy one or more objects in either
a rectangular or circular pattern and when a circular pattern is
used the objects can be rotated, it can be an incredibly powerful
command)
AutoCAD will then prompt for the type of Array - rectangular or
polar, type: P for polar. Then use the Centre snap mode to select
the centre of the circles. Then type:
4 the number of items (including the existing item)
accept 360 degrees
accept "rotate as copied"
(Centre snap After selecting the Centre snap mode, pick the
circle NOT the centre)
Figure 2 Drawing with all four "wings" in place
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Exploding Objects
Now we need to erase some of the lines we've drawn. When the
rectangle command is used the rectangle that is drawn is a
"polyline" which means that all the lines that make up the object
are joined together, the lines must be "exploded" before any parts
of the rectangle can be erased.
(For convenience, in the following section, I'll talk of the
"top-right wing" and the "bottom- right wing". By the "top-right
wing" I mean the first rectangles and arc that you drew, and the
"bottom-right wing" is the rectangles and arc in the bottom-right
corner) Select explode from the modify toolbar (or type X which is
the alias for "explode") select both the rectangles in the
"top-right corner" and then press . If AutoCAD doesn't display any
error messages then the explode command worked.
(Explode Be aware that explode does not appear to do anything!
It doesn't say - "yes, I've done that" and the display doesn't
change, but AutoCAD will display an error message if it failed to
explode the objects)
Erasing Objects
We need to delete some extraneous lines from the drawing...
Erase Select erase from the modify toolbar (or type: E ). Click
on the right edge of the inner rectangle (from the "top-right"
corner), and press . AutoCAD should automatically redraw the area
around the erased line. An alternate way to delete is to click on
the object to be deleted and then press the keyboard's "Delete"
key. Click on the line in the same place and press "Delete". (To
test your understanding: explode the two rectangles in the
"bottom-right wing" and the erase all the "inner" lines, see figure
3)
Figure 3 Lines to be erased
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Stretching . . .
Now you need to stretch the "bottom-left wing" and then remove
the inner lines.
Select stretch (or type: S which is the alias for stretch). Type
C and then draw a selection window around the arc and through the
small rectangle (see figure 4), press to terminate the selection
process, click with left mouse button near the selected objects,
and type: @-10000,0 (this is the "stretch distance"). If that
worked the building wing should stretch 10 metres (to the
left).
Stretch The "C" tells AutoCAD that you want a "crossing" window.
The normal selection window
Select only those objects wholly within the section window. A
crossing selection window selects objects that are wholly or partly
within the selection window.
A useful short-cut to know is that if you draw a selection
rectangle left-to-right (in the positive X direction) AutoCAD
interprets it as a "window" selection; but if you draw the
selection rectangle right-to-left AutoCAD interprets it as a
"crossing" selection.
Figure 4 Stretch selection rectangle Explode both the rectangles
in the "bottom-left wing" and erase the vertical lines, except the
line from the centre of the circles
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One Last Circle . . .
The last object to add is a circle inside the arc of the
"bottom-left wing". Select circle (or type: C ). Select the Center
snap mode (or type: CEN ) and click on the arc; then type 3600 (the
circle's radius).
Circle Centre snap
More Explosions and Deletions....
The drawing is basically complete; all that needs to be done is
to change some of the line-types.
Select: explode from the modify toolbar (or type X ), select all
the rectangles at the centre of the original circles (use a
crossing selection window), and then press .
Explode AutoCAD should display a message saying that some
objects could not be exploded - ignore the message - it's simply
saying that some of the rectangles have already been
There are 8 lines going to the centre (4 are "covered" by the
others). You need to erase 4 of them, select erase from the modify
toolbar (or type: E ), then click on each of the four lines and
finally press .
You should now be able to see the lines that were under the
lines you erased.
Changing Line Types
Before changing some of the lines to dashed lines, we need to
load the Linetype. Select Format - Linetype, then select "Load".
AutoCAD will display a list of Linetypes, select "Hidden" (you will
need to scroll through the list), then select "OK", then select
"OK" again to dismiss the "Select Linetype" dialog box.
Select the 4 lines going to the circle centre and the arcs in
the "top- left" and "top-right" wings (see figure 5), then select
Modify - Properties, A dialog with the properties of the selected
objects is displayed. Change the Linetype to HIDDEN and the
Linetype Scale to 75 and dismiss the dialog.
The objects should be redrawn using dashed lines (see figure
5).
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Figure 5 Final Shape
Finally...
Lastly, I want you to draw a rectangle in the diamond shape,
another diamond inside that rectangle, a circle inside that diamond
and a horizontal and vertical line also inside the last diamond
(see figure 3)! Each shape should touch the Midpoints of the
previous shape...
(Draw the rectangle by selecting from the draw toolbar or type
rectang )
HINT: To draw the circle, select Draw - Circle - 2 Points and
then (using midpoint snap) pick opposite sides of the inner
diamond.
(Alternatively select the circle icon and then type 2p then pick
the points)
Figure 4 Lab1 drawing
(If you use the MIDpoint Snap Mode for each point, you should be
able to draw the shapes without much trouble. If you make a
mistake, press "Esc" (the "escape" key, located at the top-left of
the keyboard). Then type U , the undo command)
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EXPERIMENT NO 03 & 04
Advance 2-D drawing Objective
The objective of this lab is to produce the diagram below.
During whole this procedure Ill introduce a number of AutoCAD
construction commands: offset mirror
and a number of AutoCAD editing commands: fillet, trim, break,
and extend
In case all that isn't enough for you, you will also learn about
layers, hatching, and grip editing. Layers
Most CAD systems have some kind of overlay concept. AutoCAD uses
layers. Layers are used to separate and structure drawings; layers
can be turned on and off (for example to vary the amount of detail
in a drawing), and can have Linetypes associated with them....
Figure 1: The Layer status area (Object Properties toolbar)
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When using AutoCAD, the graphics appears on the current layer,
so be careful that the current layer is correct. Look near the
top-left of the screen: the current layer and its color is
displayed there (see figure 1).
Select the Layers icon or select Format - Layers..., AutoCAD
will display the "Layer Properties Manager" dialog. Click on the
"New" button and then type CONST (to change the default "layer1"
name to something more meaningful), then click on the "Current"
button to make this the current layer.
Layers icon (The current layer is the layer to which new
graphics is added. The properties command can be used to change a
graphics object's layer)
Change the color and then "OK" the dialog box.
Draw "Construction" Lines
Draw a line from the centre: select then line icon (or type L ),
and then type: Line icon
0,0 0,-17500 @3000,0
terminate the command
Before continuing, you should "zoom in" to the lines, select
zoom-window (or type Z W ), and enclose the lines in the selection
rectangle.
Zoom Window
Select offset from the Modify toolbar (or type [the letter 'o']
O ), and then type:
Offset (The offset command makes it easy to set up a series of
grid line or (drawing) construction lines)
250 the offset distance
select the short horizontal linepick a spot anywhere above the
lineselect the new linepick a spot anywhere above it
terminate the command
This should produce one vertical and three horizontal lines.
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Revisiting Polar Array
Now you will use polar array to copy and rotate some lines.
Figure 2: The lines after using Array.
Array (under the offset icon)
Select array from the modify toolbar (or type AR ), then select
the lines just drawn by picking a spot below and to the right of
the "corner" and then another spot above and to the left or the
"corner" - make sure the selection rectangle crosses the three
horizontal lines (and the vertical line). Press to end the
selection process, type P (to specify a polar array), type 0,0 (for
the centre of the rotation), 2 (number of items), 22.5 (angle), Y
(rotate the objects).
Editing
To connect these lines select the fillet icon (or type F ), look
at the command line area: - If the current fillet radius is NOT 0
(zero) - then type R 0 (that's a zero).
Fillet icon (be careful because it looks like chamfer) If you
had to change the radius, press type to restart the command
Figure 3 Fillet
Select the outer of the three sloping lines, and then select the
bottom horizontal line. AutoCAD will
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extend the two lines until they connect to each other.
(The Fillet command is exceptionally useful. It basically
extends two lines until they meet, and optionally, inserts a curve
where the lines join)
Next, you will trim the sloping line back to the line from the
centre.
The trim command is another command that you use very often. The
first point you specify selects the "cutting edge", that is, the
line to which you are trimming back to. While succeeding selections
identify lines to be trimmed.
Figure 4: Points to be selected for the Trim
Select the trim icon from the Modify toolbar (or type TR ), for
the "cutting edge" select a spot near "first point, press (to end
the selection process), select the line to be trimmed ("second
point"); and press (to end the command).
Trim icon When picking lines to be trimmed, the part of the line
that you select is important. In the example in figure 3, if you
pick to the left of the first line selected (rather than to the
right of it), then the line will be trimmed from the fillet point
to the boundary line. In other words, you'll undo the fillet you
just did.
Repeat the fillet and trim process for the other two inner
lines.
Creating another Layer
Now you'll create a new layer, select the layers icon (or type
LA ), create a new layer and make it the current layer.
To draw the horizontal lines of the pattern, select line (or
type L ), and type 0,-6500 @5000,0 and press again (to end the
command). This line will be trimmed later....
Layers Offset icon
Select offset (or type OFFSET or just o ), type 625 (the offset
distance), select the line just drawn, click below the line to
indicate the direction of offset, and press again. Press (to
start
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another offset), type 1375 (offset distance), select the last
line created by the offset, click below the line to offset down,
and press again to end the command.
Offset this line 625 down, If that worked, you should have two
pairs of lines. These lines will form the octagonal pattern in the
centre. Continue offsetting the "last" line, using the following
offsets:
500, 750, 500, 4625, 500
That's most of the horizontal lines in the plan. Next, you will
now draw the rest of the pattern.
Firstly, offset the vertical (centre) line 2000 to the right,
and then select : trim (or type TR ), pick the vertical line just
created press (end the selection process), type F (this tells
AutoCAD that you will draw a fence line - see figure 5), draw a
fence line like that shown in the figure (it must cross the four
lines shown), after you pick the second point of the fence line,
press twice (firstly to end the fence line and secondly to end the
command).
Figure 5: Trimmed line
The following section uses a number of snap modes. The easiest
way to work with snaps is to pre-set them and then let AutoCAD
dynamically show which snap it can use...
Right-click on "OSNAP" (in the status area at the bottom of
AutoCAD's window) and select Settings then turn "Endpoint" and
"Midpoint" ON (by clicking on them). It would probably be a good
idea to turn OFF any of the other snaps that are ON. Finally, make
sure the "OSNAP" button is IN.
Select erase from the Modify toolbar (or type E ), select the
vertical line used as the "trim guide", press (end the
command).
Now you will draw the line and arc for the pattern, select line
(or type L ) then, using the Endpoint snap mode (which should
automatically be set by moving the cross-hair near the endpoint),
select the right edge of the "bottom" trimmed line and (again using
the Endpoint snap mode) select the right edge of the line above it,
then press (end the command).
Select Draw - Arc - Center-Start-End (do NOT pick the arc icon)
then, using the Midpoint snap mode select the middle of the line
just drawn, then type @0,-1800 @0,3600 . That should have drawn an
arc to the right of the vertical line.
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(The arc should start and end just "inside" the ends of the
vertical line)
Now you will use "break" to remove the part of the line between
the arc's endpoints. Select break (or type BR ), select the
vertical line, type F (to specify that the next point will be the
"first" point of the break), then using the Endpoint snap mode,
select the bottom end of the arc, and finally using the Endpoint
snap mode again, select the top end of the arc.
Break icon (Break is an extremely useful command that is used
often in editing operations)
Now draw a line (using the Endpoint snap) joining the two other
trimmed lines (see figure 6). Then trim the remaining four
horizontal lines towards the top of the bay, back to the right-hand
edge.
The last pattern is at the top of the "bay". You will need to
enlarge the view of the centre to be able to see it clearly. Select
zoom-window (or type Z W ), enter the selection window (so you can
see at least the area shown in Figure 7).
Figure 6: Lines trimmed and broken Figure 7: Grip editing
positions.
Select polyline (or type PL ), and then type 0,-600 @1000,0 ),
then using the Endpoint snap mode, pick the right-hand end of the
top horizontal line below, finally press to end the command.
Now you will use a technique in AutoCAD called "grip-editing".
Click on the lines just drawn (they'll become "dashed"), then click
on the "joint" point of the lines ("First Pick" in Figure 7),
select then Intersect snap mode, click on the position where the
horizontal line crosses the bay's right-hand edge line ("Second
Pick" in Figure 7). AutoCAD should move the selected vertex to the
intersection point.
Press the Escape key (ESC) twice to de-select the lines.
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Zoom Dynamic
One of the most powerful of the zoom options is zoom-dynamic, it
allows for zooming and panning at the same time. Type Z D or select
the command from the zoom flyout (flydown) shown in figure 8.
Move the zoom window (the cursor!) over the lower half of the
"bay" and press . If the arc has turned into a series of straight
lines then type REGEN to re-generate the view.
Figure 8 Zoom Dynamic
Draw the Boundaries
Before drawing the outer boundaries, create a new layer called
"WALLS", and set the layer's color to be something other than
white, and make it the current layer.
The boundary is 700 outside the arc pattern, so we will offset
that pattern. Offset the arc and the vertical lines on either end
(to the right) by 700. Notice that the new lines are in the floor
layer, you will need to change the lines into the walls layer.
(Don't forget to offset the line at the "top" of the arc, see
figure 9)
Select the lines and arc just created as well as the lines at
the bottom (see figure 9) - do this by click first at about the
bottom-right of the selection rectangle in figure 9 and then the
top-left point.
Figure 9: Change Properties
Selections
This should select everything except the line at the top, pick
it now. Having selected the objects, now they'll be changed to the
new layer. Go to the layers drop-down list and select "WALLS" (the
layer you just created). All the selected objects will change to
that layer. Press "Esc" (escape) twice to de-select the
objects.
Now you will join up the sections of the boundary line. Select
fillet (or type F ), select the bottom of
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the short vertical line and then select the horizontal line to
the left of the vertical line (see figure 10).
Figure 10 Fillet points (In selecting both these points, it's
important where you click on the line! The first point should be in
the bottom-half of the line, while the second point should be to
the left of the (projected) first line)
Now, use fillet on the lines shown in figure 11. Note that the
exact position that you pick is not important, but it is important
that you pick to the right (1st point) and below (2nd point) the
intersection, the part you pick (at this stage of the fillet
command) is the part that AutoCAD will not remove!
Figure 11 Second Fillet.
Select offset (or type o [the letter 'o']), and then type 250 ,
pick the bottom (of the four lines that extend to the right
edge-line), pick a position below the line to indicate the offset
direction, press to end then command.
Now you will use fillet to clean up the rest of the boundary
lines. Select fillet (or type F ), pick the short vertical line
(see figure 12), and then pick the right-hand end of the line just
created.
Figure 12 Third Fillet.
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Computer Aided Engineering Drawing 24
Restart the fillet command, pick the outer arc to the right of
the vertical, and pick the vertical (at a point above the arc).
Change the horizontal line ("2nd pick" in figure 12) into the
WALLS layer.
Lastly, you will extend the horizontal line ("2nd pick" in
figure 12) to the right edge-line. Select extend (or type EX ),
pick the right edge-line (this is the line you will extend to),
press (end the selection process), pick to the right of the middle
on the horizontal line, and finally press . Extend icon It's
necessary to pick to the right of the middle of the line because
AutoCAD extends the nearest endpoint to the "boundary edge".
Draw the Passage Between the Bays
To draw the passage-way we will firstly draw its centre line,
and then use offset to get the location of the boundaries.
Select line (or type L ), select the Center snap mode, pick one
of the arcs, type @3000,0 (to show the direction of the line),
press (to end the command).
Offset this line 500 above and below the line - so that you end
up with 3 lines, with the original in the middle.
Extend the bottom line to the right edge-line.
Select line (or type L ), select the Intersection snap mode,
pick the intersection of the outer arc and the top-most of the 3
lines; select the Perpendicular snap mode, pick the right edge-line
(see Figure 13).
Figure: 13 Bay Bottoms
Erase the top two horizontal lines, and trim the bottom line
back to the outer arc (portion right to the outer arc should be
trimmed). Finally, use Break, to remove the arc between the
remaining two lines. (Select break command and the click on the
outer arc to select it and then type f and press then the endpoints
of the horizontal lines to the right of the outer arc).
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Computer Aided Engineering Drawing 25
Finishing the Boundaries
Before hatching the boundary areas, you will need to close off
the boundaries. Firstly, you'll turn off the CONST layer.
Figure 14 Layers Drop-down list
Click on the layer status area, AutoCAD will display a list of
the layers and their status. The first icon controls whether the
layer is "on" or "off". Click on this icon beside CONST, the
'light' will go out. Then click on WALLS to close the
drop-list.
(These lines are needed because you must close off areas before
hatching them)
Now draw the lines identified in Figure 15, you may need to use
zoom or the scroll bars to get all the lines in the view. Figure
15: Lines to close of hatch areas
Hatching
Create a new layer, called hatch, and make it current (set a
different color for this layer), and then select hatch from the
Draw toolbar, make sure the pattern type is "Predefined", and set
the pattern to AR-SAND, set the scale to100, select "Pick Points",
pick inside the two areas, press to end the selection process, pick
"OK". AutoCAD should draw lots of dots, almost filling-in the wall
area.
Hatch icon
Finally, you need to erase the three lines you added to close
the wall areas so you could hatch them (see figure 15). Use the
Layer Controls to turn the "HATCH" layer OFF first. If you
accidentally pick the wrong thing, type: R (remove) to remove
selections, and then type: A to restart adding selections. Once
you've erased the three lines, turn the "HATCH" layer back ON.
That completes the basic half bay. Use zoom dynamic to view the
whole of the bay and then save your drawing.
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Computer Aided Engineering Drawing 26
Mirror the Half Bay.
To mirror the section completed, select mirror from the modify
toolbar (or type MI ), enclose all the graphics inside the
selection rectangle, press (to end the selection
Mirror icon process), type 0,0 (the centre of the building will
be the start of the mirror line), type @0,-1 (this creates a
vertical line as the mirror line, this causes the graphics to be
mirrored to the left), type N (don't delete the old objects).
Figure 16: Completed Bay
Duplicate the Bay
Before continuing, select zoom-all (or type Z A ), so you can
see the whole drawing. Then select array (or type AR ), use a
selection rectangle to select the whole bay, press (end selection
process), type P (polar array), type 0,0 (rotation centre), 8 (we
want 8 bays!), (go all the way), Y (rotate as you go). Array icon
AutoCAD will copy the single bay through 360 degrees, giving 8
bays
Last Gasps....
Zoom in on the "eastern" bay (see figure 17). If AutoCAD didn't
draw the hatching type REGEN (regenerate is similar to redraw,
except that it forces AutoCAD to carefully recalculate the screen
view, this means that curves which might to drawn "roughly" after a
zoom are redrawn as smooth curves). Erase the 4 hatching
objects!
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Computer Aided Engineering Drawing 27
Figure 17: Zoom Window.
(Remember that there is one hatch object for each half bay) You
will now draw the centerline of the doorway, select line (or type L
), select the Endpoint snap mode and pick the middle of the inner
vertical wall line, then select the Perpendicular snap mode and
pick the outer vertical line of the boundary (the line to the right
of the one just picked).
Next, offset the line 1250 "up" and "down" to make a 2500 wide
doorway; and erase the centre-line.
You will now use trim to take the vertical two lines back to the
doorway line. This is done because we want to hatch the wall area
again, so can't have any lines "sticking out".
Select trim (or type TR ), pick the doorway lines, press (end
selections), pick the vertical lines (see figure 18); and press
(end the command).
Figure 18: Lines to be trimmed Figure 19: Lines to join.
(It may be necessary to zoom out (or pan) before the hatching
becomes visible) (Remember to change the current layer to "HATCH")
Draw the lines back, but as two lines, instead of the four. We
could draw the door, but let's not bother. Now you need to draw two
lines to close off the two hatch regions. If the hatching is not
visible type REGEN . Draw lines to close off the two hatch sections
(figure 19 shows one pair of line ends).
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Computer Aided Engineering Drawing 28
Now hatch the four areas. The final output looks like:
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Computer Aided Engineering Drawing 29
EXPERIMENT NO 05
Plotting drawing in AutoCAD
Introduction
In this Lab of AutoCAD you will learn how to plot drawings. In
doing this you will learn about paper space and viewports.
Set the drawing limits from 0,0 to 50000,35000; then set the
units (set the number of decimal points to 0) and finally do a
zoom-all.
Draw the "Construction" Lines
Create a CONST layer, set its color and make it current. Draw a
18800 x 18800 rectangle (starting somewhere near the bottom-left
corner of the screen).
Draw a Circle, using the MIDpoint snap mode, pick the bottom
edge of the square, and then using the ENDpoint snap mode, pick the
top-right of the square.
Next you will draw a rectangle to complete the golden rectangle.
To do this we can use the bottom-right corner of the square for one
corner, but the other corner is more difficult: you will use
AutoCAD's point filters to take the x value from the circle and the
y value from the original square.
Start the rectangle command. Then using the ENDpoint snap mode,
pick the bottom-right of the square, then type: .X , using the
PERpendicular snap mode, pick the circle to the right of the bottom
of the square, then type: .Y , using the ENDpoint snap mode, pick
the top-right corner of the square. This technique for drawing
objects is very useful.
(The point filters that I'm introducing here are really useful -
they often provide a way to "find" positions without having to type
in numbers)
Start the line command, then using the ENDpoint snap mode, pick
the top-left corner of the square, using the MIDpoint snap mode,
pick the right edge of the rectangle, using the ENDpoint snap mode,
pick the bottom-left of the square, press to end the command.
Pick the last line drawn (near the bottom-left corner), then
pick the grip-box on the bottom-left corner (to move that
endpoint), and type: @0,1800 .
The entry will be shown as a circle about mid-way along the
bottom of the square. Start the circle command, then select the
FROM snap mode, then using the ENDpoint snap mode, pick the
bottom-left corner of the square, then type: @9800,1400 1400 . Here
you are saying that the circle's centre is to be 9800,1400 from the
bottom-left corner!
(Now you will use grip-editing to move the end of the lower line
up 1800) FROM snap mode icon
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(The FROM snap mode is really useful for specifying objects that
are positioned relative to other objects)
Now, explode the original square and then offset the bottom of
the square up 600, and then offset that line 1500 up. Then offset
the left of the square 10000 to the right.
(These are the major construction lines that will be used to
set-out the plan.)
Figure 1: The construction lines.
Draw the Walls
Create a new layer called WALLS, set its color and make it
current. Use Zoom Window to enlarge view of the plan.
The walls will be drawn using the polyline command so that you
can set the thickness of the lines after drawing them. But before
drawing the walls, you will set a running-snap. The reason for
drawing construction lines in the first place is to make it easier
to draw the walls. To make it even easier, you will tell AutoCAD to
automatically snap to line intersections, this saves you from
having to specify the snap mode for every point (though you still
need to set the snap mode when you want to use another snap mode or
none).
Select running-snap from the Object Snap toolbar (or type: OSNAP
), then select "Intersection" from the dialog box and select "OK"
to dismiss the dialog box.
Running-snap icon (Be careful not to pick "insertion".)
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Figure 2: Path of exterior walls.
Start the polyline command and pick the first five points shown
in figure 2, then type: ARC (the next segment of the polyline will
be an arc), type: SECOND this specifies you will enter a "second"
(& third) point, using the NEArest snap mode, pick the 6th
point, then pick the 7th point to end the arc. Now type: LINE (to
go back to drawing straight-lines), pick the 8th point, and finally
press to end the command.
Polyline icon (Note that the arc should be part of the polyline)
NEArest snap mode icon
Having demonstrated the running snap, let's now turn it OFF.
Select running-snap again (or type: OSNAP ), select the "Clear All"
button (below the various snap options), and then select "OK".
Turn the CONST layer OFF.
Now you will change the width of the external wall to make it a
thick line - the wall was drawn using polyline to demonstrate
polyline editing. Did you turn the CONST layer OFF?
Select Modify - Object - Polyline (or type: PE ), pick the
external wall polyline. Spend a moment having a look at the various
editing options - you can even fit a curved (spline) line to the
polyline. Type: WIDTH (or simply: W ), then type: 250 , this is the
new line-width. Press to end the command.
Turn the CONST layer ON.
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Computer Aided Engineering Drawing 32
Paper Space
You have been drawing in MODEL SPACE in your previous practices.
The significance of this is that you use real-world sizes. When
plotting, you can either specify a scale factor to plot the drawing
at a particular scale or you can use PAPER SPACE.
(During the following step your drawing will disappear, don't
panic... ) "Tile" on the status area: (Note that instead of typing
"tilemode" you can type "ti".)
Double-click on "TILE" (on the status area at the bottom of the
screen), the "TILE" should become grayed-out. Alternatively, type:
TILEMODE 0 . When this setting is ON, AutoCAD displays multiple
viewports beside each other. This allows you to have two views (of
different parts) of the same drawing on the screen. When the
setting is OFF, AutoCAD displays multiple viewports, but the
viewports are allowed to overlap each other; also viewports can be
moved, erased or resized like "normal" graphics. Turning tilemode
OFF, also changes the "MODEL" space setting (next to "TILE) to
"PAPER", indicating that you are now in "PAPER SPACE".
The advantage of paper space is that you can have numerous
drawings (or views of the one drawing), each at a different scale;
and you can draw text using "paper heights" rather than world
heights.
Set the Paper Space Limits
Lets suppose that we have a plotter with 17mm left and right
margins and 5mm top and bottom margins, this is critical. When you
lay-out your drawing you must remember that you cant draw on this
part of the page. My solution is to set the drawing limits to the
area of the page that can be drawn on (the "plotable area"), and
then draw a border equidistant from each of the paper edges.
A landscape oriented A3 sheet is 420x297mm; this leaves a
plotable area of 386x287mm. Set the limits to 0,0 to 386,287.
(Don't forget to do a zoom-all after setting the limits)
Create a layer called FRAME, set it's color and make it
current.
Draw a rectangle 20mm in from the edges of the A3 sheet; because
of the plotters 17 & 5mm margins, draw the rectangle from 3,15
to 383,272, see figure 3. The rectangle is used to position
"viewports" and then its layer can be turned OFF before plotting
(if desired).
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Computer Aided Engineering Drawing 33
Figure 3: A3 sheet with limits and 20mm border shown
Create a Viewport
Once in paper space you can create a number of views of your
drawing, with each having a different scale. But for now, you will
create just one viewport; select View - Floating Viewports - 1
Viewport (or type: MVIEW ), pick a point towards the bottom-left of
the drawing (the exact position doesnt matter at the moment), and
then pick a point towards the top-right of the drawing. AutoCAD
should show a view of your drawing. This view is at no particular
scale.
(If you want to change to size of the viewport to make it cover
more of the "paper", use grip-editing to resize the viewport. You
could use snap modes to "snap" the viewport to the drawing
border)
Return to Model Space
Double-click on "PAPER" on the status area or select View -
Model Space (Floating) (or type: MSPACE ), the "PAPER" on the
status area will change to "MODEL". Move the cursor around inside
the viewport and you will see the normal cross-hair cursor appear.
Usually, you want to have the view at a particular scale but
sometimes you simply want a particular part of the drawing to plot
and you don't care what its scale is.
(Notice that if you move the mouse cursor outside the viewport
it changes back to an arrow)
Select zoom-window (or type: Z ), enclose the entry circle in a
selection rectangle, type: REGEN - this should force AutoCAD to
recalculate the circle (and therefore display it better). If your
drawing is like mine you will see that AutoCAD has made a mess of
the line widths of the polyline around the arc...
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Computer Aided Engineering Drawing 34
Select zoom-previous (or type: Z P ), this is a particularly
useful zoom option because it's very common to zoom in on a detail
and then want to zoom back out. Of course, you could use zoom-in
and zoom-out, or zoom-dynamic if youre panning as well as
zooming.
Setting the View Scale
To set the viewport to a particular scale, you need to express
the scale, relative to the paper. If you want the view at 1:100 you
use a scale factor of 1/100 (or 0.01). Select zoom-scale from the
zoom flyout (or type: Z S ), then type: 1/100xp ), this will
produce a view at 1:100, the "xp" means "multiplied by the paper".
Select pan (or type: P ), and drag the view until the "golden
rectangle" is centered within the viewport, then press .
Zoom-scale icon (You could also type 0.01xp) Pan icon
Paper Space Revisited
Return to paper space by double-click on "MODEL" on the status
area or select View - Paper Space (or type: PS this is short for
"PSPACE").
(You may need to re-size the viewport to get the building
fitting comfortably on the page - if you haven't already snapped
the viewport to the border)
Text
Select Format - Text Style, in the top section of the dialog
select "New", click on OK (to accept the default name) then choose
a font from the Font Name drop-down list - choose a true-type font
(look for the TT icon), for example Arial, set the Height to 10,
select "Apply" then select "Close".
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Computer Aided Engineering Drawing 35
Create a TEXT layer, set its color and make it current.
Make sure you're in Paper Space, then select text (or type: MT
which is short for MTEXT), you will now enter two points that will
define the "boundary" of the text area. When you to type a
paragraph of text, AutoCAD will wrap the text to fit inside the
boundary! Pick a position below the bottom-left corner of the
building, and a second point near the right edge of the 20mm border
try to make sure there's enough height for the text.
Text icon (The Text command can also be used to add text in
MODEL SPACE, but the height of the text must be the text height x
the plot scale, for example if you want the text 5mm high and the
drawing at scale 1:100, the height must be 500)
Type: Final Diagram
You can change the properties of the text (within the dialog
box) by selecting the property that you want to alter: select
"Diagram" then select the color drop-down list (it should show
"ByLayer" at present), select a color and then click on "OK" to
dismiss the dialog box.
(Depending on the way AutoCAD is configured, you may enter the
text into a dialog box or the word processor. This section assumes
you are using the "Multiline Text Editor" dialog box)
This text is obviously wrong.
Select properties, pick the text and press , AutoCAD will
display the Modify MText dialog, take a moment to look at the
various options available.
Properties icon
Click on the "Full Editor..." button (beside the text),
highlight "Diagram", press the "Delete" key, select "OK" twice - to
dismiss the Editor and then the Modify dialog.
If the text has wrapped onto 2 lines, select properties and then
the text again, then increase the Width (try adding 10 for each
letter on the second line), then dismiss the dialog.
(You can also use Grip Editing to change the text area)
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Computer Aided Engineering Drawing 36
Figure 4: The Completed Drawing
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Computer Aided Engineering Drawing 37
EXPERIMENT NO 06, 07 & 08
Concepts and techniques used to build 3-D Models
Objective
In this Lab Ill introduces the concepts and techniques used to
build 3D models in AutoCAD. We will design a tower which features
an external spiral stair, an elaborate canopy on top, and a hole
down the centre. The final structure is illustrated in Figure 1
below. This Lab will introduce the following concepts and
techniques:
Simple solid modeling with solid primitives & CSG operations
(the tower); Construction of complex solid objects (stair and
landing); User coordinate systems and positioning of objects
(external stairs); Advanced use of the CSG operations (tapering the
stairs); Simple surface modeling (the roof canopy and handrails);
Surface modeling versus solid modeling (the handrails); Meshed
surfaces (the landing sails for shading).
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Computer Aided Engineering Drawing 38
Getting Started . . .
As with every drawing that you produce with AutoCAD you should
begin by establishing your drawing area by setting the Drawing
Limits, Units and using Zoom All to expand out to a full view of
your drawing area. Do that now, setting the limits to 20000 x
15000.
For this model, we will make use of several different layers for
handling different parts of the model. Begin by calling up the
Layer Control dialogue box and create two new layers called
Construction and Tower, setting each to a different color. The
Construction layer will be used for construction lines that do not
form part of the final drawing. The Tower layer will contain the
central tower.
Layer Control button (Hint: To create a new layer in this
dialogue box, simply click the new button and type a name for the
layer in the list. To set the color, click on the color box
adjacent to the corresponding layer)
The last thing to do before beginning the tower is to create a
single reference point for this model. We will do this by placing a
Point entity on the Construction layer at the centre of the drawing
area (which will become the centre of the base of the Shot Tower).
We will be using Points a few times in this drawing as reference
markers, so we need to set a Point Style that will be easily
visible (the normal way AutoCAD marks a point is with a single dot,
we will use an X-shaped cross instead). To do all that, proceed as
follows:
Begin by setting the current layer to Construction pull-down the
list of layers and click on Construction then proceed as
follows:
1. Format Point Style 2. Select from the pull-down menus in the
resulting dialogue box select the X-shaped cross
and then click OK. 3. Issue the Point command and click a
position at about the centre of the drawing area. 4. Escape to
cancel the command.
Draw point tool
Constructing the central Tower . . .
We will construct a 7-sided polygonal tower, 19.6 meters high (7
levels at 2700), with an outside diameter of 7 meters, and tapering
inwards at a gradient of 1:70 (which converts to an angle of 1.3
off the vertical). Proceed as follows:
Set the current layer to Tower
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[Polygon] Select from the Draw Toolbar. 7 Number of sides then
use the NODE object snap mode to fix the centre at the
point entity just created. i Specify an inscribed polygon. 3500
Radius of the polygon.
[Offset] Select from the Modify Toolbar. 300 Offset distance
select the polygon just drawn and then point to the inside to
show the side to offset press to complete the command.
We now have to extrude these two polygons in the Z-direction to
the height required, specifying the 1 in 7 taper as we do so. We
will then subtract the inner one away from the outer one to create
a polygonal shell with an empty interior.
Once we have done that, we will position a box to serve as the
doorway at ground level and subtract that away from the shell to
create the opening. That will complete the basic tower. To do all
that, proceed as follows
1. View Toolbars, Open the Toolbars dialogue box, scroll down
the list to find the Solids toolbar, and then click on the
check-box next to it. Position it anywhere convenient on the
screen, taking a moment to examine each tool, and noting the brief
description of each on the status line as you move the mouse across
them.
(Solid Modeling: With solid modeling we sculpture objects by
assembling the primitives shown on this toolbar using the three CSG
operations of Union, Difference (subtract) and Intersection. As you
will discover in this Lab,, there is almost nothing that cannot be
formed using these tools)
[Extrude] Pick the Extrude button from the Solids toolbar dont
forget to watch the prompts on the command line so that you
understand the process. select both polygons and then press to
complete the selection.
19600 Height of each extrusion. 1.3 Taper angle.
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Computer Aided Engineering Drawing 40
To see the effect of this in 3D, select View 3D Views SE
Isometric from the pull-down menus. This will create a parallel
projection (not a perspective) of the 3D object looking from the +X
/ -Y quadrant. You can then use the normal Pan and Zoom commands to
alter the screen display to suit you own purposes, while
maintaining that parallel projection. Experiment with this until
you have a 3D view of the whole tower near the centre of your
drawing area.
(The CSG tools are located on the Solids Editing Toolbar
(illustrated). You can keep this on the screen or you may feel it
is easier to execute these commands through the pull-down
menus)
2. Issue the Subtract command (Modify Solids Editing Subtract)
note that this command allows you to select two sets of objects:
the second set are then subtracted from the first we will have only
one object in each set in our case select the outer shape and press
(the primary object), and then select the inner object and press
again (the object to be subtracted from the primary one) dont
forget to watch the prompts to understand how this works.
Hide Issue the Hide command this draws the current view with all
hidden lines removed or truncated as necessary notice that your
tower is now one single solid object which is hollow down the
centre.
3. The next step is to punch a doorway through the base of the
tower. Begin by zooming in to the base of the tower with a view
similar to that shown in Figure 2, over the page (Hint: use the
real-time pan and zoom tools in the standard toolbar).
3.1. To make this process simpler, we will position the UCS as
illustrated (Figure 2), with the origin at the outside corner of
the tower and the X-axis in line with its base. To do that, follow
these steps: i) ucs Issue the UCS command to alter the position of
the current UCS. (Notice the command prompt, showing options for
saving and restoring UCS
settings.) ii) n Select the New option. Notice the variety of
ways that you can define the UCS
we will use many of these in the course of this Lab. iii) 3
Select the 3point option keyword this is the most versatile option,
allowing us
to define the new UCS precisely watching the prompts, precede as
follows. iv) |ENDpoint| Use the object snap to put the origin at 1.
v) |ENDpoint| Use object snap again to identify a point on the
X-axis at 2. vi) |ENDpoint| And again, to nominate a point on the
positive Y portion of the XY plane at
3.
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Computer Aided Engineering Drawing 41
NOTE: if the UCS icon has been placed at the origin (point 1 in
Figure 2), then type the command ucsicon and then type n for No
Origin that will force the icon back to the lower left corner of
the screen.
Notice that the UCS Icon has now dropped the W (no longer World
Coordinates) and has been positioned at the new origin, oriented to
suit the new UCS. We now use the Box primitive to construct the
doorway
(Be careful that you use the corner box rather than the centre
box)
3.2. Select from the Solids toolbar AutoCAD will prompt for the
corner position of the box. i) |ENDpoint| Use the object snap mode
to place the corner of the box at 1 in Figure 2. ii) @1400,500,2100
Specify the opposite corner of the box as a relative 3D
coordinate alternatively, this could have been done by entering
the length, width and height of the box separately.
3.3. [Move] Issue the normal Move command select the box just
created and press . Set the Base Point at the |MIDpoint| position
marked 4 (on the box just created) and the Second Point at the
|MIDpoint| of line 1 2.
3.4. [Move] Re-issue the Move command select the same object and
press and pick any point as the Base Point.
@0,-100 Specify the Second Point of the displacement to move the
box so that it is centered on the thickness of the wall.
3.5. Modify Solids Editing Subtract Issue the Solids Subtract
command pick the tower first and then press , then pick the box and
press again you should now have a door opening in the base of the
tower.
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Computer Aided Engineering Drawing 42
Constructing the External Winding Stairs . . .
The stairs have to taper inwards as they climb the tower. We
begin by building the stairs straight up with no taper, each flight
hugging the face of an imaginary extrusion (downwards) of the
7-sided polygon that forms the inside edge of the (tapered) top of
the tower: this means that at the base of the tower the stairs
actually lay partially inside the tower. Once the stairs are
complete, we will create another tapered tower in the middle of the
stairs and subtract that away from them to create the internal
taper the stairs will then very neatly follow the face of the real
tower. We then do the same with the outside taper: we build the
flights very wide to begin with, and then at the end of the process
we construct a large tapered tower with very thick walls which we
can also subtract away from the stairs, thus creating the outer
taper. This process is illustrated in Figure 12.
(Producing the taper is easy: the harder part is constructing
the stairs to begin with)
First, we need a few construction lines Make the Construction
layer the current layer again. Reset the UCS back to World (issue
the UCS command and then press to accept the default
World). Zoom out to a view that allows you to see the top of the
Tower.
We begin by tracing the inner edge of the top of the tower. To
do that, we switch on running object snap.
Tools Drafting Settings Call up the Drafting Settings Dialogue
box with the Object Snap tab. I suggest that you select each of the
ones.
(Note the brief explanation of how to use these if you have not
done so before)
[Polyline] Issue the Polyline command pick each of the 7
vertices around the inside edge of the top of the tower.
c Close the polyline. [Move] Use a Window selection rectangle to
select the polyline just drawn (you work out why!)
and then press set the Base Point anywhere you wish (well away
from everything to avoid the running object snap).
@0,0,-19600 Second point of the displacement vector.
Drafting Settings dialogue With Running Object Snap turned on,
whenever you are using the mouse to select a point, AutoCAD will
highlight and identify the nearest snap point within the snap
aperture to use that snap point
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simply click the mouse button if the snap is ambiguous, pressing
the Tab key will cycle through the available snaps at that
point.
Re-position your view to the bottom of the Tower, then, with
ORTHO mode turned on (click the ORTHO button on the status line),
construct two parallel lines of roughly the same length (as
illustrated in Figure 3) projecting out from adjacent corners of
the polygon just constructed.
Now choose View 3D Views Plan View World UCS and then zoom in on
the ends of those two lines we will use these lines to set out the
stairs in profile as illustrated in Figure 4.
[Line] Issue the Line command pick the start point at the bottom
end of the rightmost line. @0,140 Height of riser (multiple of 7!).
@-280,0 Length of going (another multiple of 7). to terminate the
Line command. [Copy] Use Window selection to select both the riser
and the going lines press to
complete the selection m Select the Multiple option with using
ENDpoint AutoSnap, set the Base Point to the base
of the riser line then place each copy at the left end of each
successive going line to form the stair flight stop just before you
reach the second construction line by pressing.
[Line] Use the Line command (still with ENDpoint AutoSnap) to
construct a line joining the bottom of the nosing to the top riser
with the bottom of the nosing to the lowest riser.
[Offset] Offset the line just constructed down by 140 to form
the soffit of the stair flight. [Line] With ORTHO on, draw a short
line from the ENDpoint of the bottom end of the lowest
riser back in the Y-direction. [Erase] Erase the right-most
original construction line and the line that was offset to
produce
the soffit line. You should end up with something that looks
like Figure 5.
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Using Figures 5 & 4 as a guides (before and after), use the
Fillet command (with radius 0) to clean up the stair profile by
joining up each of the corners. Next, we use the polyline edit
command to convert the stair profile into a single polyline entity
as follows:
Modify Polyline Issue the Polyline Edit command. Select ANY ONE
of the lines that make up the stair profile AutoCAD will note that
it is not a polyline, but will offer to convert it into one (see
the Command line) press to say yes.
j Select the Join option then use Window selection to pick all
the lines that make up the stair profile (it doesnt matter that one
has been selected twice) press to complete the selection AutoCAD
will then join all those lines to form one polyline.
Press to terminate the command.
Now turn off the Tower layer, then create a new layer called
Stair (making it a distinctive color) and set it as the Current
Layer before proceeding.
Next, use the Solid Extrude command to extrude the polyline to a
height of 2500 to form the width of these stairs and then set up a
3D view a little like the one shown in Figure 6.
(Hint: the SE Isometric view and then Zoom Window gave me a good
view) (Right Hand Rule: If you hold your right hand with your thumb
pointing in the positive direction along the axis of rotation, then
your fingers point in the direction of positive rotation)
The next step is to rotate the stair into an upright position.
Modify 3D Operation Rotate 3D
Issue the Rotate 3D command select the stair and press to
complete the selection.
x Select the X-axis option (to rotate the stair around that
axis) use |ENDpoint| to set the axis through the point 1 shown in
Figure 6.
90 Rotation angle follows the Right-Hand-Rule. [Move] Using
|ENDpoint|, move the stair using the centre of rotation point as
the Base Point
and the point on the construction polygon as shown in Figure 7
as the Second Point of displacement.
The next step is to copy and then rotate this flight to create
the second flight of stairs. We then need to
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form the landing between them, then we can duplicate the stair
all the way up the tower, and finally union all the parts together
to form a single spiral stair.
Begin by selecting a NE Isometric view & zoom in the view
shown in Figure 8.
[Copy] Select the stair flight and press pick the Base Point 1
and Second Point of displacement 2 as shown in Figure 8, using the
|ENDpoint| object snap mode.
[2D Rotate] We deliberately use 2D rotate because we only want
to rotate horizontally again, pick the stair flight that we wish to
rotate and press following Figure 8 closely, set the centre of
rotation (called the Basepoint) to point 2.
r When prompted for the rotation angle, choose the Reference
option because we want to point to the angle of rotation (rather
than calculate it, especially as it is a rather odd number) still
using |ENDpoint|, pick points 2 and 3 as the reference angle for
the new angle, we want to use the X & Y value (only) of the
point marked 4 taking its Z-value from point 2 to do that, proceed
as follows:
o .xy This is called a Point Filter (AutoCAD will only take the
XY value of the next point and then prompt you for the Z-value)
pick the point marked 4 finally pick the point marked 2 still using
|ENDpoint|).
Now is a good time to learn another way of setting up a 3D view.
We want to position ourselves to look down at the gap where we need
to construct the landing. Select View 3D Views Viewpoint Presets
You should get the adjacent dialogue box on the screen. The left
diagram shows the plan viewing angle (with the small line pointing
towards the centre showing the line of sight in plan this is set to
NE at the moment) and the right diagram shows the altitude (again,
with a small line to show the current line of sight in elevation 45
degrees). You can re-position the line of sight on either diagram
simply by clicking with the mouse.
Experiment until you get a view similar to that shown in Figure
9, remembering that this is still just a parallel projection.
A Couple of Helpful Hints Now that the model is beginning to get
a little complicated, you need to be warned that Object Snapping in
3D is a little error-prone at times (although the current version
is vastly improved in this regard). AutoCAD will sometimes snap to
the wrong point for seemingly inexplicable reasons. When that
happens, you should not despair simply cancel the command
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and start it again, the second time zooming in on the areas
concerned so that your pick points can be entirely unambiguous. It
is often a good idea to have BLIPMODE on (it is normally OFF)
because the small blips tell you if AutoCAD snapped to the correct
point. Remember also that with |ENDpoint| snaps, you dont need to
be right near the end of the entity you can often find an
unambiguous point to pick that is away from the end, but still less
than halfway along the length of the line or arc.
BLIPMODE Blips are those small marks that AutoCAD places
wherever you pick a point on your drawing. They can be turned ON or
OFF at will by selecting Tools Drawing Aids and clicking the
corresponding checkbox.
You should know all the commands necessary to construct the
landing, so I will simply describe the steps that you should
follow:
The first thing to do is set the UCS onto the plane of the
landing that is easily done using the 3Point option in the UCS
command and placing the origin at 1 in Figure 9, the X-axis point
at 2, and the third point (on the XY plane) at 3;
Next, set the current layer to Construction; Construct a short
line beginning at 1 and extending to @0,1000; Construct another
line beginning at 1 and ending perpendicular to line 3-2, and then
move that
line so that it ends at 3; Fillet the two lines just drawn to
form the outside edge of the landing; Construct a polyline that
joins points 1, 2 and 3 and then join that to the first two lines
to form a
single closed polyline around the landing; Set the Current Layer
to Stair. Finally, use Solid Extrude to form the landing slab, but
when prompted for the height pick point
1 (zoom in if necessary and use |ENDpoint|) and then the point
immediately below it on the underside of the stair flight (using
|ENDpoint| again) to SHOW the depth rather than enter a number.
Your slab was probably extruded upwards. Simply use the Move
command to move it back down to where it belongs.
We now have to fill in the gap below the bottom tread of the
second flight and the edge of the landing we just created. Using
Figure 10 as a guide, follow these simple steps:
Set the Current Layer back to Construction; Position the UCS
with origin at 1, X-axis point at 2 and
YX plane passing through 3; Construct a line beginning at 4 and
extending back up
the slope to around point 5 using the |NEArest| object snap then
move that line so that it extends down
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from position 4 (as shown in the figure); Construct the other
three lines to form the finished shape as illustrated, fillet them
and use the
Polyline Edit command to join them together to form a single
polyline; Set the Current Layer to Stair, and use Solid Extrude
with a height of -2500 to form the
required solid.
Once that is complete, use Solid Union command (Modify Solids
Editing Union) to merge the second flight, the landing and the
section under the bottom tread into one solid object. (Do not
include the original flight in the union)
Now set up a view similar to that shown in Figure 11. Reset the
UCS back to World, and using the Copy command, pick up the second
flight and position the copy using positions 1 and 2 as the Base
Point and Second Point respectively.
Then, use 2D Rotate to rotate the copy around the position
marked 2 and then use the Reference option to show the angle,
snapping to points 2, 3 and 4 in that order.
Now repeat that process, this time copying both flights 2 &
3 together to become flights 4 & 5. You can then copy those
four flights in one action to create flights 6 through 9. You can
almost complete the entire stair by copying those 8 flights to form
flights 10 through 17. You will then find that you need to copy the
top flight (only) one last time to complete the stair.
Just to see the effect, turn on the Tower layer and then use
View 3D Views Front to see the Tower in elevation view. You will
see the stairs projecting above the tower.
(Dont worry about that well fix it up later)
(Note: This whole process of copying and rotating the stair
flights to form the whole stair involves a lot of zooming and
panning. Once you have completed that process, you should feel more
competent about manipulating objects in 3D space)
The final step to complete the stairs is to union all the
separate flights together and then trim away the sections that are
not needed. With Stairs as the Current Layer, turn off each other
layer (click on the light globe symbol in the pull-down Layer
Control tool). Then issue the Solid Union command, select all the
stair entities and press . Turn the Construction layer back on, but
keep Stairs as the Current Layer.
Now set up a 3D view that enables you to see the base of the
tower and the foot of the stairs at the largest possible scale.
Construct three 7-sided polygons, centered at the Point entity at
the centre of the tower, all Inscribed, and with radii of 3510 (10
mm larger than our tower base), 4700 (1200 larger than the base of
the tower to be the width of the stairs), and 7000 (being much
larger than the outside of the stairs). Extrude each of these
polygons to a height of 25000 with a 1.3 degree taper. Next,
subtract the middle one (with radius 4700) from the outer one so
that we have an outer ring, a middle core and the stair
bridging
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between the two as illustrated in Figure 12. Finally, simply
subtract both the outer ring and the middle core away from the
stair object to create the tapered stair. Now turn the Tower layer
back on and admire what you have achieved so far.
Building the Platform . . .
Before going on to the next stage to construct the platform at
the top of the tower, I want to take a couple of minutes to
introduce the other tool that can be used to select 3D parallel
views of your model. This tool is called up by selecting View 3D
Views VPOINT (or using the command vpoint ) and results in a
display illustrated in the left margin. This is the original method
provided with AutoCAD for setting up quick views the Viewpoint
Presets dialogue is probably a bit easier to use.
To use the Tripod, imagine the object in the top right to be a
flattened globe of the world viewed from above. Position the mouse
pointer near the very centre point this is the north pole and
creates a view looking down the Z-axis (see the axes in the centre
of the screen). As you move out toward the inner ring, you are
moving toward the equator, and as you move around within that inner
ring, you are moving around and above the object (again, watch the
axes change as you move around). The outer ring represents the
South Pole (rather flattened out!). As you move about between the
inner and outer rings, you are looking up from underneath the XY
plane. If you move outside the outer ring, then the view is
meaningless.
Experiment with the tripod to move around and examine the model
so far. When you are ready to proceed, turn all layers on and zoom
in on the base of the tower so that you can see the original
reference point we created.
[Copy] Select the original reference point entity, press to
complete the selection, and then pick a Base Point anywhere.
@0,0,19600 Relative vector to place a copy of the reference
point at the top of the tower.
Now change your view so that you are looking down onto the top
of the tower. You will have noticed that the last flight of stairs
extends above the top of the tower. Since we are now going to work
up here for a while, it makes sense to move the UCS onto the plane
of the top of the tower. Using the UCS flyout, click on Origin UCS
and then use the |NODe| snap mode to pick the reference point at
the top of the tower. The axes are now orientated the same way as
the WCS, but the origin has been moved.
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The procedure necessary to construct the platform involves
commands with which you should already be familiar, so I will
simply list the steps you should follow:
Set the Current Layer to Stair, and construct a large cylinder,
centered at the new origin, and large enough to fully enclose the
top of the stair (say, 6000 radius and 10000 high) subtract that
away from the stair to truncate the top flight level with the top
of the tower.
Create a new layer called Platform and make it the Current
Layer. Construct a cylinder centered at the origin, 6000 radius and
140 high.
The next step is to cut a hole in the platform above the stairs.
You can see that illustrated in Figure 1 where the stairs reach the
top of the tower.
Set the Current Layer to Construction and, using Figure 13 as a
guide, construct a 7-sided polygon centered at the origin 1 with an
inscribed radius set by using the .xy point filter with |ENDpoint|
and picking the outer-most point 2 on the top-most landing of the
stair (and then picking any point on the XY plane of the UCS to
specify the Z-value).
Switch back to the Platform layer and use that polygon, along
with the outside edge of the top of the tower, to construct a
polyline around the opening that needs to be created above the head
of the stair use Figure 1 to see roughly where I placed the opening
you can size yours how you like, provided you allow enough headroom
over the stairs.
(Hint: you need about 15 risers to create enough headroom: that
is, the short top flight, the full flight below that, and the first
few steps of the flight below that)
Extrude the polyline up to height of 200 and move it down by
about 20 so that it protrudes both above and below the platform
slab (remember the earlier comment about avoiding thin slivers of
material?), and then subtract it away from the platform slab.
Finally, cut a circular hole about 2000 in diameter at the
centre of the platform slab (through which the blobs of molten lead
would be dropped!).
That about does it for the platform in the next section you will
learn how to do some simple surface modeling.
Surface Modeling, Columns, Platform Handrails & Roof . .
.
We choose now to construct the columns and handrails that
enclose the platform as surface objects (called meshes). They could
be constructed as solids just as easily, but the way AutoCAD
represents curved solids tips the balance in favor of surfaces. To
get a feel for that, do a hide looking at the platform you just
created notice that the curved edge is triangulated, which would
look a bit strange on a round column or handrail. To cancel the
hide, use the Regen command.
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A brief comment on strategy at this point: because the columns
and handrails are very repetitive, we will create one column with
two pieces of handrail attached to it, save that as a block and
then simply insert instances of that block all around the platform.
That will conserve memory space since the complex geometry is only
being stored once, but being used around 20 times.
It would be appropriate now to close the Solids toolbar and open
the Surface toolbar instead.
Begin by moving the UCS origin up by 140 to the top of the
platform slab (but keeping it at the centre). Then create a new
layer called PlatformColumns, set the Current Layer to
Construction, and freeze all the other layers except Platform,
Construction and PlatformColumns (so that they are invisible &
ignored by AutoCAD).
We will model the columns as a tabulated surface mesh. These are
meshes that are created by projecting (or extruding) a curved
entity (referred to as the path) along a direction vector. In our
case, the path will be a circle in the plane of the platform, and
the direction vector will be a line up the centre of the column
(see Figure 14). Note that the direction vector must be a simple
line, but does not have to be perpendicular to the plane of the
path. Equally, the path does not have to be closed for a tabulated
surface mesh. Ours is actually a very simple application of a
tabulated surface.
The curved handrail segments will be modeled as surfaces of
revolution. These take a generating path (in our case it will be a
circle) and sweep it through an arc (up to 360 degrees) around an
axis. We will use a vertical axis positioned at the centre of the
platform (as illustrated in Figure 14). As with the tabulated
surface mesh, the generating path does not have to be closed as you
will see later, the canopy roof over this platform is also created
as a surface of revolution using an open polyline as the path.
We need to begin by drawing some construction lines (illustrated
in Figure 15 over the page):
Draw the axis line from the centre top of the platform (should
be the origin of the current UCS) straight up to a height of around
4000.
Draw a circle, centered at the base of the axis line with a
radius of 5850.
Draw another circle centered at the west quadrant point