Appendix 5: Editing Dimensions – Machine Drawing with AutoCAD

Appendix 5

Editing Dimensions

EDITING DIMENSIONS IN AutoCAD

We shall first start with typical situations where a need for change of dimension label arises.

Suppose there are three objects in your drawing with dimensions as shown in Fig. A5.1. To modify the dimensions do as follows.

 

FIG. A5.1   Need for editing dimensions

 

  1. Fig. A5.1a Change the overall sizes of the arrowheads and text heights or change arrows to tick or dot mark.
  2. Fig. A5.1b Change the position of the text “D” so that it does not cover the center line.
  3. Fig. A5.1c Change the font style or the text height as per requirement.

Editing the different components of a dimension entity can be achieved with the following commands.

EDITING DIMENSION TEXT—DIMTEDIT AND DIMEDIT COMMANDS

Dimtedit

This command can be used for changing the placement, justification, and rotation angle of a single dimension text object. It is applied only at one dimension at a time.

 

AutoCAD Commands and Prompts Steps/Feedback/Options
Command: Dim ↵ Tedit ↵ Initiates the DimEdit command.
Select Dimension: Pick a single dimension.
Specify new location for dimension text or [Left/Right/Center/Home/
Angle] :
Enter an option which is self-explanatory.
  Home is used to place the text in its default position. You can pick a new location or drag the text to the new location with the cursor. Angle option allows you to place the text at a particular orientation.

Dimedit

This command is more versatile than Dimtedit and is used for manipulating the text and extension lines of selected text objects. It can be used on more than one dimension at a time.

The prompts are as follows.

AutoCAD Commands and Prompts Steps/Feedback/Options
Command: Dimedit Initiates the command.
Enter type of dimension editing [Home/New/Rotate/Oblique] <Home>:  
Select objects: Select an option, or if you want to bring all text back to the default position (Home), press Enter.
  Select dimensions and dimension text to edit. All the options are self-explanatory.

Option New   If you select the New option, the Mline Text Editor opens, and the existing text position is shown within brackets. You can replace the existing text by typing over the brackets. If your new text is placed outside the brackets, before or after, it will be appended to the previous text.

Option Oblique   It is widely used in Isometric drawing. First, dimensions of an isometric drawing are provided following the general rules of dimensioning (Fig. A5.2a). However, it is necessary to change the orientation of the extension line (Fig. A5.2b) as per drawing convention. This can be done using the Oblique option of the Dimedit command. The desired angle of extension line (measured with respect to the positive X axis) has to be supplied at the “Enter Oblique angle < press Enter for none >:” prompt. The orientation of the extension lines will be modified accordingly.

 

FIG. A5.2

USING GRIP TO EDIT DIMENSION

You can Stretch, Rotate, Scale, Trim, and Extend all dimensions by using Grips. You can move the Dimension text by using Grips. The steps are as follows.

  1. Select the Dimension object, so that the Grips are displayed.
  2. Click the grip located at the Dimension text making it a hot grip. The Stretch grip editing mode becomes active (watch the display at the command line).
  3. Stretch the dimension text to a new location.
  4. Press Esc twice to clear grips.
USING OBJECT PROPERTIES WINDOW

You can change almost all the system variables of a dimension by selecting the dimension by clicking it and then opening the Object Properties window by selecting it from the Modify Properties option. The window lists all the variables and you can incorporate your change in the proper box. You can resume your drawing by pressing Esc twice.

MODIFYING OR OVERRIDING THE DIMENSION STYLE

Dimension style   You should have a very clear concept about the Dimension Style while using dimensioning in AutoCAD. AutoCAD has two default dimension styles, namely, Standard and ISO-25 for ANSI and metric unit users, respectively. Both styles have some specific features such as height of text, size of arrowheads, type of arrows, overall scale factor, dimension scale factors, zero suppression, different types of fits, and so on.

All dimensions that you place in the drawing are created using the current settings of the Dimension style. You can, of course, change the setting to suit your purpose, save the new settings under a named Dimension style, and restore them for reuse.

You can control dimension system variables either by entering the variable name directly at the command line or by using the Dimension Style Manager dialog box shown in Fig. A5.3. It can be accessed by the following commands.

 

 

The general principle for working with the Dimstyle Manager box is very simple. If you want to make a particular style current, pick the style from the style list and click the Set Current tab to make it activated. You can get a preview of the chosen style also in the Preview box along with a description below it. Let us concentrate on other tabs as well.

 

FIG. A5.3   The Dimstyle Manager dialog box

 

New   This option allows you to set your own dimension style and save it with a name in the Create New Dimension Style dialog box shown in Fig. A5.4. Generally, you start with an existing style and then modify or override some of its features to suit your purpose. Mention the tips of dimensions for which your changes will be effective–either Linear or Angular, or any other or for all dimensions in the Use for box. If you select only a few dimension types for the new style to be effective, then it actually becomes a sub-style of the original style and you are not allowed to give a new name. Then click Continue to open the New Dimension Style dialog box to select settings for the new style.

 

Modify   As mentioned before, if you modify (see Fig. A5.3) any style, then, it will be imported to all the dimensions in the drawing for which you have used the style. The modified settings become the current settings too. Once you press the Modify button, the Modify Dimension Style dialog box opens and you are allowed to edit the settings. Click Close to return to your drawing to start dimensioning with the new modified style.

 

FIG. A5.4   New Dimension Style dialog box

 

Override   This is same as above. However, a style is not modified permanently. You just override the style for a lesser number of uses or to update some of the old dimensions by using the Update command. Here too start with a style. Click the Override button to open the Override Current Style Manager dialog box to change the current settings. Remember that by this option you do not change the current style, you just override it. Click Close and return to your drawing to override the current setting or to update the old dimensions.

 

Compare   You want to compare your present style with other style(s). After making all the changes, pick the Close button to return to your drawing.

CONTROLLING THE DIMENSION SETTINGS

In order to modify or override a style, you have to change the settings of the current style. Before you learn to do that, you must know that the settings of any Dimension Style comprises the following six tabs. They are opened only when you click the New, Modify, or Override tab of the Dimension Style Manager dialog box.

 

1. Lines and Arrows tab It controls all the features of the lines and arrows.
2. Text tab It controls all the features of the dimension text.
3. Fit tab It controls how the arrows, extension lines, text will be arranged or fit in your dimension label.
4. Primary Unit tab It controls the dimension, Scale factors, Precision Zero suppression, Units format, and so on for linear and angular dimensions.
5. Alternate Units tab Sometimes it may be required to define your measurements in Alternate Units, that is, in mm and inches together. In such cases, you control the formatting using this tab.
6. Tolerance tab This is used for Tolerance dimensioning, discussed in detail in the chapter on production drawing.

 

The entries to be made against individual tabs are simple and self-explanatory. For most entries, you will get an immediate preview of the modifications done in the large preview box placed at the top right of the tab display box.

NOTE

The Overall Scale Factor entry in the Fit tab controls the overall sizes of the arrowheads, text size, spac-ing, and so on. It has no bear-ing upon the actual measurement recorded.

 

Fig. A5.5   New Dimension Style dialog box

 

After you have made the changes, click OK to go back to the first dialog box (Dimstyle Manager dialog box) and then click Close to go back to your drawing. There are tabs (Fig. A5.5) such as Text, Fit and Primary Units to control other parameters of the dimensions.

 

 

Measurment scale   This entry in the Primary Units tab controls the scale factor of the measurement. If you enter 2 here, a line drawn to a length of 10 units in the drawing here will show a measurement of 20. Similarly, if you enter 0.5 here, the same line will show a measurement of 5.

Update   Once your modification of the dimension style is complete, you may want to update some of your old dimensions to the new settings. This is done as follows.

At this command AutoCAD will prompt Select objects: Pick the dimension you want to update.

Examples   We give below a few examples of various options of the settings that you may create by means of Dimension Style dialog box.

 

FIG. A5.6   Modifying Text and Arrows in Dimensioning