Dimension line arrowheads are AutoCAD blocks. (See chapter 13, “Using Blocks and External References.”) AutoCAD provides 19 arrowheads that you can use, but you can also create and use your own arrowhead blocks. AutoCAD inserts the block in the arrowhead location and sets the object’s X and Y scale factors to arrowhead size × overall scale. To trim the dimension line, AutoCAD inserts the rightmost block with a zero rotation angle for horizontal dimensions and rotates the leftmost block 180 degrees about its insertion point. If you use paper space scaling, AutoCAD computes the scale factor before applying it to the arrowhead size value.
The following example shows how to create a three-stroke arrowhead. Setting Snap mode to half a drawing unit and setting the grid to one drawing unit makes block creation easier. You create the block for insertion as the right arrowhead of a horizontal dimension line.
The illustration shows a right-angle (or three-stroke) arrowhead with a one-unit grid for clarity. The block’s insertion base point is at the point where the dimension line and the extension line intersect (in the illustration, at the tip of the arrowhead).
The dimension line stops arrowhead size × overall scale drawing units away from the extension line. Consequently, the block consists of an arrowhead and a short horizontal tail line connecting to the dimension line.
To create your own arrowhead symbol
- Draw the arrowhead so that it measures exactly one drawing unit from the insertion base point at the tip of the arrowhead to the end of the tail.
- From the Draw menu, choose Block Make.
- Enter a block name for the symbol.
- For the insertion base point of the block, specify the point you want placed at the intersection of the dimension line and the extension line (where the tip of the default arrowhead would be).
- Select the objects for inclusion in the block.
Command line BLOCK
To use your own arrowhead symbol
- From the Dimension menu, choose Style.
- In the Dimension Style Manager, choose New or Modify, depending on whether you are using the arrowhead for a new dimension style, or modifying an existing dimension style.
- In the New Dimension Style or Modify Dimension Style dialog box under Arrowheads, select User Arrow.
- In the Select Custom Arrow Block dialog box, select the arrowhead from the list.
- Choose OK to complete the modification.
The Select Custom Arrow Block dialog box displays a list of blocks within the drawing.
To use a custom arrowhead block for the second arrowhead, repeat steps 3 and 4, choosing User Arrow in the 2nd arrowhead list.