Graphics Programs Reference
In-Depth Information
mension to turn on its grips. The grips on the objects being dimensioned are on
the dimension's definition points. Because you wouldn't want these points to ap-
pear when you plot your drawings, the Defpoints layer has a special property:
Nothing created on the Defpoints layer will print.
Because of the Defpoints layer's non-printing property, experienced users
have been using it for years as a place to put sketches, guidelines, and important
notes (for example, “Don't forget to buy bread on the way home!”). I don't endorse
this practice because a convoluted relationship exists between the Defpoints lay-
er and Layer 0 — it can be very hard to tell what's on which layer, and that can
make the drawing harder to edit. If you want a “scratch” layer for those important
notes, create one named Scratch and set it to NoPlot in the Layer Properties Man-
ager palette. (For more about layers and the Layer Properties Manager, see
Chapter 6.)
A field guide to dimensions
AutoCAD provides several types of dimensions and commands for drawing them. Figure
14-3, earlier in this chapter, shows the most common types, and the following list de-
scribes them:
Linear dimensions:
Indicate the linear extent of an object or the linear distance
between objects. Most linear dimensions are either horizontal or vertical, but you
can draw dimensions that are rotated to other angles, too.
Aligned dimensions:
Similar to linear dimensions, but the dimension line tilts to
the same angle as a line drawn through the origin points of its extension lines.
Radial dimensions:
A
radius
dimension shows the radius of a circle or an arc, and a
diameter
dimension calls out the diameter of a circle or an arc. You can position
the dimension text inside or outside the curve, as shown in Figure 14-3. If you posi-
tion the text outside the curve, AutoCAD (by default) draws a little cross at the
center of the circle or arc. As shown in Figures 14-2 and 14-3, AutoCAD automatic-
ally adds the diameter and radius symbols to the appropriate dimension type.
If you're wondering when you should use which, because radius and
diameter dimensions seem to do the same thing, the convention in most drafting
