AutoCAD Mechanical toolset provides AMPOWERDIM to create radial dimensions and diameter dimensions for arcs and circles, as well as arc length dimensions for arcs.
When you create a radius or diameter dimension for an arc, it is not necessary to position the dimension line along the arc directly. If you place the dimension off of an arc resulting in the dimension pointing outside the arc, the program draws an extension line that follows the path of the arc being dimensioned. To suppress the creation of extension lines, set the DIMSE1 system variable to ON.
As you place radius or diameter dimensions in the drawing area, you can select placement options, enabling you to specify the appearance of the dimension. For example, you can choose place diameter and radius dimensions inside or outside the circle or arc.
If the arc or circle is so large that it is not practical to draw a radius dimension from the center, create a jogged radius dimension. This dimension enables you to begin the dimension line at a location other than the center of the arc or circle you are dimensioning (1). Once a jogged radius dimension exists, you can modify the jog (2) and the center location override by grip editing the dimension.
In addition to the AMPOWERDIM command, you can use AMPOWERDIM_RAD for radius and arc length dimensions, AMPOWERDIM_DIA for diameter dimensions and AMPOWERDIM_JOG for jogged radius dimensions. With AMPOWERDIM, use command line options to select options for these dimension types. The other commands skip the first selection steps, but they are identical to AMPOWERDIM in all other aspects.