Back to basics: Extrusion in AutoCAD part 4

The last option to cover within Extrusion is Path. This will take four complete posts, but I think it’s worth examining the options very carefully.

Last time we talked about Direction, which would somehow do the same as Path, if the latter was a simple segment. If you have a polyline, 3dpolyline or spline, then Path is the right option.

Let’s see how it works.

First of all… where do we locate the path? Well, there are some rules for that.

Normally, the path will be located in a point that touches the profile. The path does not need to actually start in the profile, but it normally helps to better understand what you are doing. However, this may vary. You could have the path starting at a midpoint in one of the segments of the profile, or even have the path starting anywhere, and at some point intersecting the profile. Actually, the command will also work with a path which does not touch the profile! The result may not be too predictable, but there’s always a rule for that too (but not today).

 

Let’s assume that the path starts at the bottom vertex of this rectangle. Once we invoke the Extrude command, we need to add the path, since what we’ll see by default is the dynamic preview of the profile extruding along its normal. Once we access Extrude options (down arrow, right click if you use mouse sensitivity, or command prompt), we select Path, and then click on the entity which will act as path. And voila!

  

This is the before and after selecting the path (images above and below respectively)

 

Let’s see what happened in this process. If we go to a Top View, we’ll see that the angle between the profile and the path was kept. I have heard people asking why (in a similar case) the ending of the extrusion is not vertical. Well… that’s not the way the command works. If you need something like that, a loft between two profiles and a guide would be better.

 

Does this work in any case? Let’s try with this other arc, which starts almost tangent to the profile. Almost is the magic word here. Since it is not tangent, the command works perfectly, as you can see in the two images that follow.

 

In the following image, we can see a scenario where the command will fail. The path intersects the profile, and it will be impossible not to generate a self intersecting solid. That’s something that AutoCAD will not accept. Some applications can force the creation of a non valid solid, but that will lead to problems at some point.

 

One last case for today. The following path and profile don’t have any trouble in creating an extrusion. But if we move the path to the other end of the profile, it will fail, since the path’s curvature is smaller than the length of the profile, which will evidently cause a self intersection. Pretty obvious, but tends to happen, and sometimes in the middle of a very long day, we may oversee this kind of conditions that Extrude with Path needs for a successful operation.

In the two images that follow, the command succeeds, while it fails with what seems a small change in the starting conditions (last image).