Computer Aided Engineering Drawing (CAD)

Federal Urdu University of Arts, Science & Technology Islamabad Pakistan Electrical Engineering

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



Name: ____________________________________________

Registration No: ____________________________________

Roll No: ___________________________________________

Semester: _________________________________________

Batch: ____________________________________________



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



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"(!!).



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)



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



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



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



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:



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



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



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



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



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).



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)



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)



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.



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



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



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.



(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.



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



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.



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).



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.



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!



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).



Now hatch the four areas. The final output looks like:



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



(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".)



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.



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).



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...



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".



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)



Figure 4: The Completed Drawing



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).



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



[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.



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.



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.



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



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.



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



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



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



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



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.



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.



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

Computer Aided Engineering Drawing (CAD)

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