utoCAD Tutorial 3:FOR RELEASE 14
utoCAD Tutorial 3:
FOR RELEASE 14
PLEASE READ: ___________
These tutorials were designed to be part of the introductory courses taught by the Graphic Communications Program at NORTH CAROLINA STATE UNIVERSITY. All of the directions used in this, and the other tutorials in this series, assume that you are running AutoCAD Release 14 on an NT system. These directions will only work with Release 14. Other versions may not have the same commands or format.
OBJECTIVES:
After completing this tutorial you should be able to:
- define, reorient, and utilize the User Coordinate System;
- create a simple solid model from primitives and combine them using Boolean Operations;
- use the HIDE command to remove hidden features in a solid model;
- use the RENDER command to add shading to a solid model; and
- insert a titleblock around the model and print it.
STEP 1
To work effectively with CAD programs, such as AutoCAD,
you must be able to create three-dimensional models of an
object and convert them to two-dimensional drawings. One aspect
of AutoCAD, and many other CAD programs, is that the creation of a model
relies heavily on your understanding of the Cartesian
System (X-axis, Y-axis, and Z-axis)
and your ability to relate it to the model in space. In this program you
must change the orientation of the X, Y, and Z planes to suit the needs
of the drawing process. In AutoCAD, variations of the Cartesian
System are referred to as the User Coordinate
System (UCS). The User Coordinate System allows you to reposition
the location of the origin point (0,0,0) and the X, Y, and Z axes during
the model's construction.
In the last two tutorials you worked with two-dimensional (flat) drawings and AutoCAD's default coordinate orientation, referred to as the WORLD Coordinate System (WCS). One of the main objectives of this tutorial will be to give you some experience creating and using User Coordinate Systems (UCS), which are coordinate systems defined by the user. There are some AutoCAD elements you cannot place or modify unless you change the UCS orientation first.
Look at FIGURE 1, which displays the World Coordinate System (WCS) icon you have been seeing in the AutoCAD drawing area. You may have noticed it before, but until now you did not need to be concerned about it. Since you were working in a two-dimensional world, the default XY plane orientation was sufficient for your drawings.
Notice the letter W on the icon in FIGURE 1. This W indicates that you are in AutoCAD's WORLD Coordinate
System (WCS). Since this is AutoCAD's default coordinate orientation,
a new file in AutoCAD always opens in the WORLD Coordinate orientation and
displays the WCS icon.
FIGURE 1
The WORLD Coordinate System (WCS) icon also labels the positions of the X and Y axes. The Z-axis, which is not labeled, lies perpendicular to the other two. In a default file, the POSITIVE (+) Z-AXIS is perpendicular to the computer screen and points towards you. If you understand this relationship, you can understand how to reposition the X, Y, and Z axes to form a User Coordinate System (UCS).
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In this orientation, notice that the X-axis is aligned at the 0 degree mark on a flat 360 degree XY plane. Your position IN this flat XY plane is at the 270 degree mark, but you are also at a 90 degree angle FROM the XY plane or looking straight down the Z-axis. If you look at FIGURE 3, you will see that this position is slightly deceptive. |
FIGURE 2 |
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Think of the front of your screen, in this orientation, as a table top flipped up on its side. Fortunately, it is a virtual table top so you do not have to worry about things sliding off. You must become comfortable with this orientation for the World Coordinate System to use the User Coordinate System. NOTE: AutoCAD uses this "plan view" as its default orientation because it was originally designed for architectural drawings, and this orientation was appropriate for drawing floor plans. |
FIGURE 3 |
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In AutoCAD, the coordinate orientation and your viewpoint of a model are independent of each other. You can change your viewpoint of the model without changing the model's coordinate system. This is like repositioning a camera to take a photograph of an object that is lying on a table without moving the object on the table, i.e. without changing the object's coordinates. In FIGURE 4 the eye represents the default view point of an individual to the model as described above. Notice that the eye is looking straight down at the model. The image seen from this vantage point would look like the one in FIGURE 5, which appears to be a 2D drawing of the object's top. Look again at FIGURE 4. Notice the WCS icon and its orientation to the model. Although for this example I changed the Viewpoint so the model would appear three-dimensional, the orientation of the WORLD Coordinate System has not changed; therefore, the location of the XY Plane has remained the same. **When you work with solid models, you must constantly be aware of the orientation of the coordinate system so you can correctly add new or modify existing features.** Later in this tutorial, you will change your viewpoint (Vpoint) and the coordinate system in order to construct a simple model. **If you do not understand some of these concepts, you need to read this information again.** |
FIGURE 4
FIGURE 5 |
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Look at FIGURE 6 to see a right hand in its proper arrangement, with labels for the X, Y, and Z axes. The thumb, index finger, and middle finger are pointing in the POSITIVE direction of each axis. These fingers are held at a 90 degree angle to each other with the THUMB as the X-axis, the INDEX Finger as the Y-axis, and the MIDDLE Finger as the Z-axis. By holding these fingers in this position, and changing the position of your hand, you can see the relationship of the axes when the coordinate system is changed. (See FIGURE 7). Try placing your fingers in the position shown in FIGURE 6 and then rotate your hand so that you change the axes to the position illustrated in FIGURE 7. FIGURE 6 would be the correct position for the X and Y axes to be oriented to the FRONT of an object. This orientation would have to be defined by the user, and, therefore, would be a User Coordinate System. FIGURE 7 would be the World Coordinate System, which is the same as a coordinate system with the X and Y axes oriented with the TOP of the object. Finally, try to position you hand for a RIGHT SIDE orientation. |
FIGURE 6
FIGURE 7 |
STEP 2
To begin your model, locate and open
your copy of the start_page file.
Use Save As... to rename it acadtutor3.
To see if you have a grasp of the User Coordinate System, and give you some experience with modeling in AutoCAD, you will change your viewpoint in the acadtutor3 file. The standard view is aligned with the World Coordinates. Your new viewpoint will provide a "pictorial" view of a model similar to the one in FIGURE 4.
Read the information on the Viewpoint (Vpoint) command and use its Rotate option to rotate your view to 300 degrees IN the XY plane and 35 degrees FROM the XY plane. FIGURE 8 illustrates the change in your view to a model. Your view after completing this operation will look like the one in FIGURE 9. (Note: Your WCS icon may be in a different position than the one shown in the illustrations.)
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FIGURE 8 |
FIGURE 9
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Notice that the cross-hairs on the screen are now at a skewed angle (see FIGURE 9). This indicates that your Viewpoint is different, but the WCS has not changed.
To help you visualize your position even better, let's turn on AutoCAD's grid. Find the Status Line at the bottom of the screen, and double click on the GRID button. The letters will turn BLACK when grid is on, and dots will appear on the screen. See the FIGURE below.
You also should see that the dot pattern (GRID) matches the WCS. The
cross hairs and grid are always aligned with the WCS or UCS.
NOTE: If your viewpoint is perpendicular to the current coordinate
system's XY plane, so you are looking at its edge, the grid disappears and
the UCS or WCS icon is replaced by one that looks like a broken pencil,
see the FIGURE to the RIGHT .
STEP 3
To begin assembling your model, you will first create
a BOX.
The Box command is one of a class of commands known as PRIMITIVES. Primitives are simple shapes that can be combined or subtracted from other solids, through a process known as BOOLEAN Operations, to create a more complex shape. Many software programs use Primitives and Boolean Operations to model objects.
You will use several Primitives to create your model. ***WARNING:*** Getting these features in the correct place will depend on whether you correctly orient your coordinate system, so work through this section carefully.
To help you work with primitives, you can display a SOLIDS toolbar, like the Osnap toolbar you used in the last tutorial. Locate the View pull-down menu, and then select Toolbars... The Solids toolbar is one of many you can display on the screen though this command. You also can customize toolbars through the Toolbar dialogue box. Find the name Solids, and click on the check box to its left. As soon as the Solids toolbar appears, close the Toolbar dialogue window. Move the Solids toolbar to an appropriate location by holding down the left mouse button on its top edge and dragging it.
Before creating your first primitive, look at FIGURE 10 to see what it should look like after you complete the next set of instructions.
FIGURE 10
To create a box, you will use the Box
command. Read the information on the Box command by clicking on
the Box link.
Now, follow the prompts to add a box that starts at the 0,0,0 point.
Note the addition of the THIRD number, which is the Z axis. You must also work in the Z-axis when working with solids.
The box's second corner should be placed at 60,40, which is the opposite diagonal corner of the Box's base on the XY plane, and its height should be 40.NOTE: When creating primitives in AutoCAD, the Height is always along the Z-axis of the coordinate system used. The value for the height can be a positive or negative number, and its sign dictates in which direction the primitive is projected.
Now, check your drawing against FIGURE 10. If your figure does not match, erase it and try again.
Notice that the box you created appears to be transparent. This is just one of the ways that AutoCAD can display a model.
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model is being displayed in WIREFRAME mode. See FIGURE 11 (on
the RIGHT) for another example of a model displayed as a wireframe.
WIREFRAMES show only the edges of a model, so the model appears to
be transparent. You can think of the lines that make up a WIREFRAME as "wires"
that indicate the model's edges, hence the name. Wireframes can be difficult
to interpret because they are transparent; however, they are easier for
the computer to display, so they are AutoCAD's default method of displaying
a solid model. If the model was always displayed as an opaque solid, it
would slow down the operation of the program because of the number of calculations
the computer would have to perform to generate the image. |
FIGURE 11 |
HAVE YOU SAVED YOUR FILE LATELY?
STEP 4
You will now add a second box centered with the first.
Because the orientation of this box will be the same as the first (in World
Coordinates) you will not have to change the coordinate system before adding
it.
You will use the Box
command again, but instead of drawing the box from corner to corner, you
will add it about a center point. To find the center of the original
box, you need to add some construction lines. Look at FIGURE 12 to
see where to add these lines.
Notice that two lines have been drawn diagonal across the top and bottom of the box (use the Endpoint Osnap), and one line connects the top line's midpoint (use the Midpoint Osnap) to the bottom line's midpoint.
**NOTE: The Intersection Osnap will NOT work with a solid model.
FIGURE 12
With these lines inserted, you are ready to use the Center
option of the Box
command to add the box. Consult the information of the
Box command again before inserting
this second box. Now, use the midpoint 
Osnap to locate
the center of this box at the midpoint of the vertical construction line
you just added. The second corner of the box should be at @-20,-10,20.
Look at FIGURE 13 to see how the box should look when you are done.
FIGURE 13
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Help!! My second box is wrong!! If your second box is not the correct size and shape, or it is not centered with the larger box (which means your box is not the correct size and shape) you probably made one of two possible errors:
Erase the box and then try to add it again, keeping these possible errors in mind. |
Now, erase the construction lines you used to locate the center for the second box.
HAVE YOU SAVED YOUR FILE LATELY?
You will use the second box you added to cut a rectangular hole through the first. The command you will use for this operation is called the Subtract command and is a Boolean Operation. Read the information on this command before you start.
Use the Subtract command to remove the smaller box from the bigger one. Look at FIGURE 14 to see how the figure should now look.
Hint: Read the description of the prompts for this command carefully. The prompts will direct you to select the solid or solids you want to subtract another solid or solids FROM (the larger box) and then to select the solid or solids you want to subtract (the smaller box). If you are not paying attention, it is easy to get these reversed.
FIGURE 14
After you use the Subtract command, the model doesn't not look any different, so let's check your model by using the Render command. This is a second way that AutoCAD can display a solid model, and it is also a good way to see if you completed the last command correctly. Because the model you are working on is displayed as a wireframe, you cannot tell if the smaller box was actually removed from the larger one.
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Look at FIGURE 15 to see how a model looks when Render is used. Read the directions for the Render command and use it to render your model. Yours may not be this color. When you have completed viewing the model, use Escape (Esc) and then type regen at a Command: prompt to refresh the model and remove the shading. |
FIGURE 15 |
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FIGURE 16, to the RIGHT, illustrates the look of a model when the Hide command is used. Use the Hide link to read the procedures for using this command and then apply it to your model. It is not necessary to use regen after the Hide command. AutoCAD will return your model to a wireframe appearance when you activate another command. |
FIGURE 16 |
If the Render or Hide commands revealed that the model was not correct, undo the last steps you completed and try again.
STEP 5
To add the next feature, you must change the User Coordinate Orientation so the XY Plane is oriented to the Front
face. To do this, you will use the 3-point option of the UCS command to create
a Front UCS. Read the information on the the UCS
3-point
option before attempting this. You will need to select the corners of the
outside box in the order they are numbered in FIGURE 17 during this
procedure. The UCS icon should be oriented like the
one in FIGURE 19 if you completed the 3-point option correctly.
FIGURE 17
With the coordinate system changed, use the UCS command's Save option to save this UCS configuration under the name FRONT. This will allow you to use this coordinate system without having to go through the 3-point option again.
To see if you have saved it properly, type dducs at a Command: prompt. If the Front UCS was saved, the UCS Control dialogue box should list the World, Previous, and Front coordinate systems. See FIGURE 18.
NOTE: Anytime "dd" is at the beginning of a typed command, AutoCAD will display a dialogue box.
FIGURE 18
STEP 6
With the UCS oriented
to the Front of the model, you can add a cylinder, with the Cylinder
command 
, through this side of the model.
To locate the cylinder, you need to add a construction line diagonally across the front surface of the box (as seen in FIGURE 19). The cylinder will be located at the midpoint of this construction line.
FIGURE 19
Before adding the cylinder, read the information on the Cylinder command.
Now, add a cylinder at the Midpoint of the diagonal construction line that has a radius of 10 and a height of -50.
Notice the use of the negative number for height. The cylinder height, which is along the Z-axis, must be negative so it will be projected into the model. A positive height value would project the cylinder forward so that it sat on the front of the box's face.
After adding the cylinder, erase the diagonal construction line.
Use the Subtract command to remove the cylinder from the rest of the model. See FIGURE 20.
NOTE: 
If your model does not match the one in
FIGURE 20 after the last Subtract operation,
then you did not subtract the smaller box from the larger one earlier. If
you subtract it now, the model will still be correct.
FIGURE 20
HAVE YOU SAVED YOUR FILE LATELY?
STEP 7
To carry out the next step, use the UCS command to change
back to the World Coordinate System. One way you can make this change
is to type dducs at a Command:
prompt, select *World,* click on the CURRENT button,
and then on OK. Check the UCS icon for the W to be sure you made the change properly.
The last primitive you will add to the model is a small Box on its RIGHT FRONT CORNER.
Look at FIGURE 21 to see where this box will be placed. Use an Osnap to locate the front corner of the box on the XY plane and a Relative Rectangular Coordinate to locate the second diagonal corner of the box on the XY plane. The first corner should be located at the bottom of the right front corner of the existing model and the second corner should be 15,15 from the first corner of the box. Give it a height of 20.
FIGURE 21
To integrate this box into the model, you will use another Boolean Operation, the Union command. Read the information on this command and use it to connect the box to the rest of the model. NOTE: The line on the front surface, separating the two parts, should disappear. See FIGURE 22.
FIGURE 22
Save your file!
STEP 8
With the model complete, you are ready to insert your
titleblock. Before this, you will change the UCS once more so the model
will be correctly oriented to the titleblock. The easiest method for
accomplishing this is to select the View
option under the UCS
command. The View option will orient the
UCS to your current viewpoint.
Now, use the Insert command to place you titleblock around the model; however, when inserting the titleblock scale it along the X and Y axes .5 (half size). See FIGURE 23. You may have to use the Move command to center the titleblock around the model.
BE SURE TO READ THE SPECIAL PRINTING DIRECTIONS BEFORE YOU PRINT THIS FILE!!!
FIGURE 23
Once the titleblock is placed, you must Explode it
before you can edit the text. Use ddedit to edit the text in the
block as needed.
Special Printing Directions:
AutoCAD has difficulty sizing the print of this model using the printing configuration you have used in previous tutorials. Below is a list of the settings you should use for this tutorial and a method for centering the image on the paper.
Print settings:
__ Units should be on MM.
__ Rotation should be at 90 degrees.
__ Pen Assignment should have Color 7 changed to .7.
__ The Scale to Fit box must NOT be checked.
__ Scale of drawing should be 2:1. (You have to double the size of the print since the titleblock is half its original size.)
__ To position the drawing,
click on the button at the lower part of the Plot dialogue
box labeled Window...
The Window Selection
dialogue box will appear with a button in the upper Left corner
labeled Pick.
Click on
the Pick button, and the drawing should reappear.
Use an Endpoint or Intersection
Osnap to select the diagonal corners of the titleblock.
The Window Selection dialogue box will reappear listing the absolute
coordinates of the the corners you selected.
Finally, click on the OK button
to return to the Plot dialogue box.
__ Check to see if the drawing in centered with Full Preview, and then Exit the preview window by clicking with the RIGHT mouse button in an empty space on the screen so the Option dialogue box appears. Select Exit.
__ Now, in the Plot dialogue box, click on OK to send the drawing to the printer.
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**IMPORTANT CONCEPT: When you inserted the titleblock, you scaled it by .5, which is half size; therefore, you must print your drawing in a 2:1 (twice as big) scale to make it the size of the paper. If you enlarge or reduce the size of the titleblock when you insert it around a drawing, you must reverse the process when you print. FOR EXAMPLE: If you inserted your titleblock with a X and Y scale factor of 2, you would have to print the drawing in a scale of 1:2. Since the titleblock was inserted at twice its original size, you must reduce it by half to print it on an 8 1/2 X 11 sheet (A Size) sheet of paper.** |
Congratulations! You have now finished Tutorial 3.
Solid models are a lot of fun, aren't they?
In the next tutorial, you will learn how to convert a solid model to a Multiview Drawing.
AutoCAD is a registered trademark of AutoDesk, Inc.
AutoCAD Tutorial 3: For Release 14 was written by:
Dr. Alice Y. Scales, Ed. D.
Graphic Communications Program
Department of Mathematics, Science and Technology Education
NORTH CAROLINA STATE UNIVERSITY
With contributions by Russell R. DownsThis work is copyrighted and the property of Alice Y. Scales and is not to be copied without permission of the author.
7/27/98
Revised 6/28/00
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