Tuesday, 16 June 2015

DIMASSOC: Keep Dimensions Dynamic

Dimensions can be both the most convenient or most bothersome aspect of CAD annotations.  Today, lets look at an AutoCAD variable setting that should help DIMinish your anxieties.

Guilty by Association?
First, it is worth noting that dimensions in AutoCAD can be placed as intelligent, dynamic objects that react to changes in your drawing, or can be nothing more than an arrangement of lines and text that gives the appearance of a 'normal' dimension.

The AutoCAD variable that controls the behaviour of dimensions is DIMASSOC.  The value of DIMASSOC at the moment a dimension is created sets the property for the dimension.

DIMASSOC can have a value of either 0, 1, or 2.

DIMASSOC is a drawing variable, which means it's value is set separately in each drawing; it is not stored in any dimension style.

A setting of DIMASSOC of 0 means that created dimensions are exploded to lines, solids and text.  This is rarely a desired output, since it is not dynamic.  DIMASSOC of 1 means that created dims behave as one object, and will update as the positions of the dimension are adjusted, but does not update if the OBJECT it is dimensioning is modified.  DIMASSOC of 2 creates dimensions as single objects that will automatically follow modifications to the object it is dimensioned. 

Let's observe the difference in the following example:

The figure below shows two linear dimensions, each appearing the same as the other.  The dimension above the line has DIMASSOC=1, and the dimension below has DIMASSOC=2.

Both dimensions will update if the dimension grips are picked and the dim is grip edited. 

In the next figure, the bold line has been stretched 25 units to the right.  Note the upper dimension, with DIMASSOC=1 has not changed, but the bottom dimension with DIMASSOC=2 has automatically followed the object.

Setting DIMASSOC 2 makes your drawings and dimensions 'smarter!"

If you happen to have a dimension that is not associated to the object it describes, you can associate it with the AutoCAD command DIMREASSOCIATE.  This neat command will prompt for dim objects to re-associate, then prompt for the locations on the objects.  AutoCAD will then re-associate the dimensions.  FANTASTIC!

What's your DIMASSOC set at? Share your thoughts and  experiences.