Dimension & Extension Lines

Dimension & Extension Lines
[CA, TL,CCT, CF]


img1.jpg (59613 bytes)

Dimension Lines - show the direction and extent of the numerical size. They are thin lines and terminate with an arrowhead at each end. A single style of arrowhead should be used throughout the drawing.

Extension Lines - are used to extend a surface or a point beyond the outline of the object so that a numerical size can be related to that surface. A small gap is left between the extension line and the outline to which it refers.

Dimension Placement

Normally, dimension lines should be broken for the insertion of the dimension that indicates the distance between the extension lines. An alternative (though not recommended) is to place the dimension above or to the outside of the dimension line.

img6.jpg (5988 bytes)
Preferred Method

img7.jpg (7858 bytes)
Preferred Method

img5.jpg (7493 bytes)
Not Recommended
img8.jpg (6397 bytes)
Not Recommended

When adjusting formatting options for all dimensions in AutoCAD, use Format - Dimension Style - Modify.

img18.jpg (85821 bytes)

If you wish to adjust the formatting for a single dimension only, select the dimension with your left mouse button, and then right click anywhere on your screen and select Properties. You can then adjust the formatting for the specific dimension.

img19.jpg (25987 bytes)

Dimension Spacing and Alignment

Dimensions that are consecutive must be aligned.

img9.jpg (6684 bytes)

On occasion it is necessary to stagger parallel dimensions to avoid crowding.

img11.jpg (6844 bytes)
crowded dimensions
img10.jpg (7854 bytes)
staggering prevents crowding

When staggering dimensions, place the shortest dimension closest to the outline.

img12.jpg (8506 bytes)
shortest dimension closest to object

Avoid dimensioning to hidden lines unless it is absolutely necessary. Usually the hidden feature is visible (and can be dimensioned) in one of the other views.

img13.jpg (8142 bytes)

Dimension lines should be placed outside the view whenever possible except when readability is improved by placing it inside the view.

img14.jpg (5514 bytes)
preferred
img15.jpg (8073 bytes)
not recommended

A small gap is left between the extension line and the outline to which it refers.

img16.jpg (7308 bytes)

Center lines may be used as reference points when dimensioning to circular references. However, when you snap a dimension to the end point of a center line, you will notice small gaps in between the dimension and center lines (see below).

img17.jpg (22019 bytes)
notice the gaps between lines

To fix this problem, select the affected center line with your mouse and then select the handle at the end of the center line and snap it to the endpoint of the extension line. Note: you may need to explode the center line using the explode tool before you can select the handle.

img25.jpg (16772 bytes)

img26.jpg (25023 bytes)
gaps properly filled

Angular Units

Angles should be measured in degrees. Generaly, angular dimensions should be placed off of the view except when readability is improved by placing it inside the view.

img34.jpg (5432 bytes)
Dimension placed off the view

img35.jpg (5520 bytes)
Sometimes placing dimensions in the
view improves readability. When doing
so make sure that the dimension does not
interfere with internal drawing detail.


Last Updated June 6/2001