Autodesk AUTOCAD 2006, Command Reference Manual, Page: 486 / 1490

Path
Selects the extrusion path based on a specified object. The profile of the selected
object is extruded along the chosen path to create solids.
profile
path
Select extrusion path: Use an object selection method
Lines, circles, arcs, ellipses, elliptical arcs, polylines, or splines can be paths.
The path should not lie on the same plane as the profile, nor should it have
areas of high curvature.
The extruded solid starts from the plane of the profile and ends on a plane
perpendicular to the path at the path’s endpoint. One of the endpoints of the
path should be on the plane of the profile; otherwise, the path is moved to
the center of the profile.
If the path is a spline, it should be perpendicular to the plane of the profile
at one of the endpoints of the path. Otherwise, the profile is rotated to be
perpendicular to the spline path. If one of the endpoints of the spline is on
the plane of the profile, the profile is rotated about the point; otherwise, the
spline path is moved to the center of the profile and the profile rotates about
its center.
If the path contains segments that are not tangent, the program extrudes the
object along each segment and then miters the joint along the plane bisecting
the angle formed by the segments. If the path is closed, the profile should lie
on the miter plane. This allows the start and end sections of the solid to match
up. If the profile is not on the miter plane, the profile is rotated until it is on
the miter plane.
Profiles with multiple loops are extruded so that all the loops appear on the
same plane at the end section of the extruded solid.
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