How to Add a Datum Symbol in AutoCAD Dimensioning

Datum symbols are used in dimensioning to indicate reference geometry, such as planes, surfaces, or edges, used as a reference for displaying a set of tolerance values.

AutoCAD supports many geometric dimensioning and tolerancing symbols within the feature control frame, and you can easily add feature control frames using the Tolerance option on the AutoCAD dimension panel; unfortunately, however, AutoCAD doesn’t have a built-in option for adding a datum feature symbol.

To add a datum symbol in AutoCAD, we can make use of multileaders.

To add a Datum symbol to a drawing in AutoCAD, we need to improvise a bit. In this article, we’ll look at two simple methods for adding a Datum feature symbol in AutoCAD; let’s start with the Multileader option.

Adding a Datum Symbol with Multileader

Using Multileader:
To create a datum feature symbol, we need to create a new Multileader style. Type MLS in the command line and press Enter. In the Multileader Style Manager window, click the New button, then name the new style MULTI and click Continue.

Click the Leader Format tab and find the Arrowhead panel, then select Datum triangle filled from the Symbol drop-down menu, as shown in the image below.

Select the Leader Structure tab, then click the Maximum leader points box in the Constraints panel and enter 2. Uncheck the box. In the Landing settings panel, uncheck the Automatically include landing option, as shown in the image below.

Now go to the Content tab and click the Frame text box in the text options panel, as shown in the image below. Click OK, then Close, to exit the Multileader Style Manager window.

Select this multileader style as the default and create a multileader; it will resemble a Datum feature symbol

Now, as shown in the figure below, click the Multileader command button in the Leaders panel of the Annotate tab on the ribbon, and select the geometry in the drawing area where you want to place the leader..

Click where you want to place the datum symbol’s letter. The cursor will start blinking, prompting you to enter text for the datum symbol. Enter the letter (text) you want. Now you have a “datum” symbol in the drawing area.

Using a Block with an Attribute

In this method, we’ll create our own Datum feature symbol using a Block and its attributes. Create a geometry resembling the datum symbol, then type ATT in the command line to launch the attribute definition window.

In the Tag field, at the Identifier letter prompt, type A, and leave the Default field empty. Set the text justification to Middle Center and set an appropriate text height, then click OK to accept these changes. Click the middle of the rectangle in the datum feature symbol to place the tag.

Now turn this geometry, along with the attribute definition, into a block. This block can now be used as a datum symbol whenever needed, and every time you insert this block, it will prompt you to specify the identifier letter. You can also rotate this symbol using the Rotate command to place it on different planes.