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. The UCSICON, which you have seen displayed so far, is a three-dimensional icon. Although it has some advantages because it displays the Z-axis in some views, we will switch to the more traditional two-dimensional icon provided by AutoCAD for the discussions of the UCSICON.	FIGURE 1
Type ucsicon at a Command: prompt. The prompt will read: Enter an option [ON/OFF/All/Noorigin/ORigin/Properties] <OFF>: type the letter p, for Properties, and press the Enter key. The UCSICON Properties dialogue box will appear. Now that you have the UCSICON Properties dialogue box open, click on 2D (See Figure 2) to change the icon to a 2-dimensional version of the icon. The 2D makes it easier to tell when you are in AutoCAD's default orientation or World Coordinate System (WCS).
Notice the letter W on the icon in FIGURE 3. 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. The WORLD Coordinate System (WCS) icon also labels the positions of the X and Y- axes. The Z-axis, which is not labeled on the 2D icon, 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).	FIGURE 3

Look at Figure 2 (to the RIGHT) which again shows the WORLD Coordinate System icon. 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

In reality, you would be looking at a top view of a model or drawing in AutoCAD when your point of view matches the default WORLD Coordinate orientation. See FIGURE 3. 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

To see a solid model as a three-dimensional object, you must adjust your viewpoint (using AutoCAD's Vpoint command) to the model. 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

One of the best ways to remember the relationship of the X, Y, and Z axes is the RIGHT HAND RULE. This rule uses three fingers on the RIGHT hand, each finger representing an axis. 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 the classtemplate file you created in the Tutorial 1.

Use Save As... to rename it acadtutor3.

Click on the Model tab, next to the Layout1 tab, to move to MODEL Space. Your model must be created in Model Space, since it is 3-dimensional space.

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.)

FIGURE 8

FIGURE 9

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 click on the GRID button. 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.

Your 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 second box. Consult the information of the Box command again before inserting this second box. Be sure to select the Center option by typing the capital letters of this option. 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

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: — either you forgot to used the midpoint Osnap to select the center for the box on the vertical line, OR — you did not select the Center option before giving the box's coordinates. Failing to select the Center option is the most common error made. After evoking the Box command, the first prompt is Specify corner of box or [Center] <0,0,0>:. At this prompt you must type a "ce" and then press Enter to indicate that you want a box created about a center point. 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.

The Render command adds shading to the surfaces of a model. Since this consumes a great deal of memory, it should only be used occasionally to check your model. AutoCAD will return the figure to a wireframe, but you must type regen at a Command: prompt to return the model to a normal wireframe appearance. 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

The third way that AutoCAD can display a solid model is with the Hide command. The Hide command removes the hidden lines in a model so that it appears opaque. It is a quicker way to check your model for errors than the Render command. 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 UCS (User Coordinate System) so the XY Plane is oriented to the Front face. There are two ways to do this. One way is to type ucs at a Command: prompt, select the orthoGraphic option and then Front.

The second way is to type dducs at a Command: prompt, which will bring up the UCS dialogue box. See FIGURE 17. Now,, select the Front UCS orientation in the UCS dialogue box.

Look at the UCSICON on the AutoCAD screen to be sure the UCS changed.

FIGURE 17

NOTE: Anytime "dd" is at the beginning of a typed command, AutoCAD will display a dialogue box.

STEP 6

With the UCS oriented to Front, you can add a cylinder, with the Cylinder command , through this side of the model. NOTE: The UCS change was needed before you could add this cylinder because the circular base of a cylinder is always oriented with the XY plane of the current UCS.

To locate the cylinder, you need to add a construction line diagonally across the front surface of the box (as seen in FIGURE 18). The cylinder will be located at the midpoint of this construction line.

FIGURE 18

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 19.

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 19

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. You can make this change by typing ucs at a Command: prompt, and selecting the World option. 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 Wedge on its RIGHT FRONT CORNER. To understand how the Wedge command works, you will need a little explanation. The Wedge command will prompt you for the two diagonal corners of the base of the wedge. The next prompt will ask for the wedge's height. Wedges tend to be oriented in one direction. Therefore, you will create the wedge, rotate it into a new position, and then move it to its final location.

Read the information on the WEDGE command before you start.

With this information, activate the WEDGE command. Locate the first corner of the wedge at the Right Front corner of the existing model. When prompted for the next corner, use a relative coordinate to place this corner at 30,30 and 20 for the height. See FIGURE 20.

FIGURE 20

The WEDGE you just added is not in the orientation that is needed, so you need to ROTATE it and then MOVE it into the correct position.

We will begin by using the Rotate command to turn the wedge -90 degrees. Read the information on the Rotate command before we start.

To rotate the wedge you will follow the prompts that first ask you to select the object you wish to rotate. Next, a prompt will instruct you to select a Base point. The Base point is the position on the wedge that you will rotate the object around. You should use the Endpoint Osnap and the front left corner of the wedge as its Base point. See FIGURE 21. Finally, the prompt will ask you for the degrees of rotation. Use -90 so that the figure will rotate into the correct position. NOTE: You could also have used 270 degrees to rotate the object to the same position.

FIGURE 21

Your figure should look like FIGURE 22 when you are finished.

FIGURE 22

The next step will be to move the wedge into position. To change its position, you use the MOVE command. Read the MOVE command before you begin. When using the MOVE command to move the wedge, and select the Front LEFT corner of the wedge as the Base point for the move. See FIGURE 23.	FIGURE 23
Finally, select the Front LEFT corner of the box as the point to align the wedge with. See FIGURE 24.	FIGURE 24
The final figure should look like the one in FIGURE 25.	FIGURE 25

STEP 8

      To finish the model, you will add a cylinder to the middle of the sloped surface of the wedge. Because the base of a cylinder is always aligned with the XY plane, and we want to have the cylinder parallel with the top of the wedge, you must reorient the UCS to the face of the wedge.

AutoCAD allows you to place a UCS anywhere you need it to accomplish the task you need. To place the UCS, we will use the 3Point option of the UCS command. Reread the information on the UCS command.

Activate the UCS command, select the New option and then 3point. Look at FIGURE 26. When the prompts ask for a new origin point, use an Osnap to select the point labeled as 1. When asked for a positive on the new X-axis, select the point labeled 2, and when as for a positive position on the Y-axis, select the point labeled 3. When you are finished, the UCS will be oriented to the figure as it is in FIGURE 27.

FIGURE 26

FIGURE 27

With the UCS aligned with the slope of the wedge, construct a line from one corner of the sloped surface of the wedge diagonally to the opposite corner of the same surface. See FIGURE 30. Use the Midpoint of this construction line to place a cylinder that has a radius of 5 and a height of -20. Once the cylinder is placed,

FIGURE 28

FIGURE 29

Subtract the cylinder from the wedge.

To finish the figure, you will use the UNION command to connect the wedge to the rest of the model. Read the information on the UNION command and then complete the model.

FIGURE 30

Erase the construction line used to place the cylinder.

STEP 9

    With the model complete, you are ready to insert it into your titleblock.

Move to Layout1 by selecting the Layout1 tab. If the model appears in the layout, click on the viewport edge and erase it.

Next, use the VPORTS command to create a Single Viewport that fills the drawing area of the titleblock. HINT: Remember to select the opposite diagonal corners of the drawing area for the corners of the viewport.

In Layout1, click on the edge of the viewport to select it. HINT: Remember you can click on the upper edge of the titeblock to select this viewport because it overlaps the edges of the titleblock image area. Now, locate the Viewport Toolbar and select a scale of 2:1 in the Scale window to scale the model size. Finally, if the model needs moving, use the PAN command to adjust its position in the window.

     Once the model is centered in the titleblock, you must Explode it before you can edit the text if it is not already exploded. Use ddedit to edit the text in the block as needed. Remember, you need to change the size in the SCALE: section to match the size of the figure inside the titleblock or 2:1. See FIGURE 31.

.

FIGURE 31

FIGURE 32

You are now ready to Plot your drawing, but first we will make two additional settings.

The first setting you need to make will remove the hidden edges in the model when it is printed. To remove these edges, you will use the Properties command. To make this change, again select the edge of the viewport containing the model if it is not already selected. Now, type prop or at a Command: prompt or select Properties on the Modify menu. The Properties dialogue box will appear. See FIGURE 32.

In this dialogue box, locate the listing, Hide plot. NOTE: It does not matter if the Alphabetic or Categorized list is used, since this heading appears on both lists. Click in the block to the Right of Hide plot heading and a Drop-down menu will appear. Click on the drop-down menu arrow and select Yes. Close this dialogue box. Now, select the Plot command and make the selections that are listed in the Plot information.

The second setting you need to make will remove the contour or mesh lines that are added to solids in AutoCAD when a solid is printed with the Hide plot setting is selected. Normally your print with Hide plot selected would look like the model in FIGURE 33. To remove these so that the model will print, as the one in FIGURE 34, you will use a command called DISPSILH (Display Show silhouettes). To access this command you can either type dispsilh at a Command: prompt or select Options... and then Display Show silhouettes in wireframe under the Tools menu. The prompts will read: Enter new value for DISPSILH <0>: Type 1 and press Enter.

FIGURE 33

FIGURE 34

Use the Plot command and make the appropriate settings to print the model. You can check these settings by reading the information of the PLOT command again. Check the look of the drawing by selecting Full Preview and then click on OK to send the drawing to the printer.

 

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.

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AutoCAD is a registered trademark of AutoDesk, Inc.

AutoCAD Tutorial 3: For Release 2000i was written by:
Dr. Alice Y. Scales, Ed. D.
Graphic Communications Program
Department of Mathematics, Science and Technology Education
NORTH CAROLINA STATE UNIVERSITY

This work is copyrighted and the property of Alice Y. Scales and is not to be copied without permission of the author.

9/5/01

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