Unit 15: Using Symbols and Attributes

Transcription

1 Unit 15: Using Symbols and Attributes Overview Many mechanical drawings use the same geometry over and over. The SI symbol, commonly found on Metric drawings, is one example. AutoCAD allows you create an object such as the SI symbol and import it into other drawings. You can also attach information to a drawing, such as the manufacturer and price of a specific object. Objectives Create an SI symbol for use in metric drawings. Insert an SI symbol into a drawing. Attach information to a nut with attributes. Introduction The ability to use common geometry over and over is another big advantage to using a CAD system over mechanical drafting. If you manage you files and drawings properly, you should never have to draw an object more than once. Another advantage over manual drafting is the ability to attach information to an object. You also have the option of displaying this information on the screen or plot, or having it remain hidden. You can also extract this information into a spreadsheet or database. Section 1: Creating and Inserting a Block of the SI Symbol Blocks, which can be used to represent symbols, are created like any other object using your standard drawing and editing symbols. A block is defined as a single object, composed of many other objects. You can also block objects from other drawings and insert them into the current drawing. If you know the geometry you are creating will be used again, create a block of it. File management is obviously a very important concept when dealing with blocks. When you create a block, you must give it a name and store it in a location you can find later. The ability to use the same geometry in more than one drawing is only effective if you can find the blocks you created! Creating a Block of an SI Symbol All metric drawings contain the standard SI symbol shown in figure The SI symbol is a good candidate for a block, since it is used repeatedly. To create a block of the symbol, you first need to draw the symbol. If you already created it in a previous drawing, you can access that drawing and block the symbol directly from the drawing. You do not have to re-draw something to create a block of it if it has already been created. 1

2 Fig The SI symbol, commonly found on a metric drawing. The first step in creating a block of the SI symbol is to determine the insertion point. A good location would be the center of the small circle. This insertion point is used when the block is inserted into a drawing. The block appears on the screen with the screen crosshairs at the insertion point. After creating or finding the symbol on another drawing and determining the insertion point, issue the WBLOCK command. This will create a separate drawing file of the objects you define as part of the block. You can access the WBLOCK command by: Typing wblock at the Command: prompt. After invoking the WBLOCK command, the Write Block dialog box appears. It is very important that you select the correct drive and subdirectory where you want to store the block. You also need to name the block. Don t include a file extension since AutoCAD automatically adds one. The Write Block Dialog box is shown in figure Fig The Write Block dialog box, with *.dwg as the output file type. 2

3 After entering the file name and selecting the correct drive and path, you need to determine the insertion base point. At this point you can enter the coordinates, or select the Pick Point button. Selecting the Pick Point button will return you to the drawing editor where you can select the center of the circle using CENter object snap. After selecting the insertion base point, you need to select the object that will comprise the block. Choose the Select Objects button to return to the drawing editor wher you can use any object selection method (such as window, fence, crossing window) to pick all of the objects that make up the SI symbol. Inserting the SI Symbol into a Drawing After creating a block of the SI symbol, you can insert it into a drawing. When you insert the SI symbol into a drawing, you must specify four things: The name, drive and path of the SI block. The point where you want the SI block inserted. The rotation of the SI symbol. In most cases this will be zero. The SI block scale in the X-, Y-, and Z-axis. This will vary, depending upon the scale of the drawing you are inserting the symbol into. The SI symbol should always plot at the same size. For example, if the drawing you are inserting the symbol into has a scale factor of 4, you need to scale the X- and Y- axis by 4. To insert the block into the current drawing, use the Insert dialog box shown in figure You can access this dialog box by: Selecting the Insert Block button on the Draw or Insert toolbar. Type insert at the Command: prompt. Select Block from the Insert pull-down menu. Fig The Insert dialog box, used to insert the SI symbol into the current drawing. 3

4 To insert the SI symbol into the current drawing, select the Browse... button in the Insert dialog box. This accesses the Select Drawing File dialog box as shown in figure Change to the correct drive and directory and choose the door symbol file. When you are returned to the Insert dialog box, you have the option of entering the insertion point, scale, and rotation of the resistor block in the dialog box or at the Command: prompt. By default, the Specify Parameters on Screen box is checked, which will return you to the Command: prompt. If you know the insertion point, scale, and rotation, you can enter this information directly in the Insert dialog box. Fig The Select File dialog box, used to select the SI block. If you leave the Specify Parameters on Screen box checked, you are returned to the drawing editor and prompted for the Specify insertion point or [Scale/X/Y/Z/Rotate/ PScale/PX/PY/PZ/PRotate]:. The insertion point for the door symbol is the end of the resistor, which was specified when the block was originally defined. As you move the crosshairs, AutoCAD dynamically moves the resistor symbol on the screen. You can select the insertion point on screen, or type in the absolute coordinates where you want the door block inserted. You can change the Scale factor for the symbol by entering an S at the prompt. Enter the scale factor of the resistor symbol. Remember, the scale factor for the resistor symbol should be 1, which is the default. By entering X, Y or Z you can enter different scale factors. You can also Rotate the symbol by entering an R. Many times you will have to rotate the symbol to align with the other objects. 4

5 Section 2: Adding Information to a Nut Symbol with Attributes Another common symbol found on mechanical drawings are bolts and nuts. The procedure for creating a symbol with attached attributes is similar to the procedure used to create the SI symbol. Creating an attribute to associate with a nut involves the following steps: 1. Create the nut using your geometry creation and editing commands. 2. Define the attribute using the ATTDEF or DDATTDEF commands. 3. Use the BLOCK or WBLOCK commands to convert the nut objects and attributes into a named block. When the Select objects: prompt appears, select all of the drawing objects and attributes. 4. Insert the nut and associated attributed into the current drawing using the INSERT command. Creating the Nut Symbol The first step is to create the nut symbol shown in figure If you already have a nut symbol on another drawing, you can use it. Creating the Nut symbol was explained in Unit 6, Creating Basic Geometry. Fig The completed nut symbol. Defining the Nut Attributes To define an attribute for the nut, first do one of the following: Select the Define Attributes from the Block, Draw pull-down menu. Type ddattdef at the Command: prompt. Either method will access the Attribute Definition dialog box as shown in figure For both attributes, use the Standard style, with a height of 1/8. We will use the following values for the first nut attribute: 5

6 Fig The Attribute Definition dialog box, used to enter all attribute definitions for the nut. Mode: Invisible Tag: MANUFACTURER Prompt: Who made this nut? Value: Erickson Use the following values for the second nut attribute: Mode: Invisible Tag: COST Prompt: What is the cost of the nut? Value: $0.75 Check the Align below previous attribute box. At this point the drawing looks like figure 15.7, with the nut and two defined attributes. Fig The nut with two defined attributes. 6

7 Creating a Block of the Nut and Attributes When creating a block of the nut and attributes, use the same procedure described for making a block of the SI symbol. When adding attributes to a block, however, first select the attributes individually. This will insure you are prompted for the attributes in the correct order. After selecting the attributes, select the objects that make up the nut. Inserting the Block of the Nut and Attributes When inserting the nut and attributes block, use the same procedure described when the SI symbol was inserted. The only difference is you will be prompted for the cost and manufacturer of the nut, allowing you to confirm the cost and manufacturer. If the ATTDIA system variable is set to 1, the prompt will be displayed in a dialog box. If ATTDIA is set to 0, you be prompted for the values at the Command: prompt. After inserting the nut, the attributes will not appear on screen because both attributes were defined as invisible. To see the attributes, set the ATTDISP prompt to ON. All attributes are now visible as shown in figure Fig The inserted nut symbol, with both attributes displayed. Unit Review When you are working on your CAD drawings, you should never have to draw something more than once. Proper use of the WBLOCK command allows you to save specific parts or a drawing for use in other drawings. A drawing created with the WBLOCK command is no different than any other drawing. You can also use the WBLOCK command to create a symbol library consisting of common mechanical parts. Many commercial symbols are also available for use in AutoCAD drawings. In addition to creating a WBLOCK of an object, you can also attach information to it with the use of the attribute functions. The attribute information can be displayed on the screen, or hidden. You can also extract the attribute information for use in a bill of materials or a pricing schedule. 7