Part 8
Module 37: Dimensioning- Part 1
Learning Outcomes
When you have completed this module, you will be able to:
- Define the 11 basic dimensioning terms.
- Describe the properties of associative and exploded dimensions.
- Apply the DIMASSOC and DIMSTYLE commands to control and modify the appearance of dimensions.
- Create a dimension style and set the dimension variables for both an english and metric drawing.
- Apply the BREAK and DIMCENTER commands to draw center lines.
Dimensioning
Dimensioning is the process of adding size descriptions to objects in the drawing. After the dimensioned are inserted, the layout can be plotted and used for construction or reference. Up to this point in the book, only shape description have been defined to the object by describing its size and location. Since AutoCAD knows the exact size of the objects in the drawing, you only have to enter the type and location of the dimension you want to insert and AutoCAD will do the rest.
Since there is a lot to learn, dimensioning is a complex but not a difficult subject. Therefore, in the AutoCAD 2D book, only learning to control the appearance, inserting, and editing the basic dimension types is taught. When you complete the AutoCAD 2D book, you will be able to completely dimension a drawing for most applications.
Associative verses Exploded Dimensions
An associative dimension is intelligent, similar to an associative hatch pattern. They are tied to the object they are dimensioning. An exploded dimension is simply a collection of AutoCAD drawing objects indicating a measurement on the object. It has no relation to the object it is dimensioning. An associative dimension and exploded dimension do not appear any different on the drawing and you cannot tell them apart by looking at them. The differences between them are as follows:
- The dimensions of objects dimensioned with associative dimensions, when modified with most editing commands, will change to reflect the changes to the size of the object. The dimensions of objects that are dimensioned with an exploded dimension, when modified, will not change.
- Associative dimensions are harder to edit than exploded dimensions because they are inserted as blocks. An exploded dimension is inserted with individual drawing objects. If an associative dimension is exploded, it will be converted into an exploded dimension.
- If the properties of the dimensioning style of an associative dimension is modified, all dimensions on the drawing, using that style, will change. For example, if the user changes the height of dimension text, change it once in the dimensioning style and all existing associative dimensions, using that style, will automatically display the new size.
Definition Points
Definition points are points that are automatically inserted on the drawing when an associative dimension is inserted. One definition point is inserted for each end of an extension line or on opposite sides of a circle or an arc. The points are autom