Back to basics: Extrusion in AutoCAD

After some weeks of adjustment and some sleep deprivation, I'm back with more tips and (hopefully) useful data about modeling in AutoCAD.

Talking about extrusion seems a little too basic, but I still need to cover some basics about it in order to get to more advanced topics.

The Extrude command has been around for some time already, and also allows other options than just the basic operation of generating a model that makes use of a profile and uses the normal to that profile as path.

AutoCAD 2007 introduced real time preview of the operation, and also introduced a couple of new controls in order to manipulate the extruded geometry. The real time preview can be seen in the image below. Once you select the profile, you will be able to define the height, or also access other options. It is important to clarify that the preview only happens if you select a single profile for extrusion. If there are multiple profiles selected, Extrude will prompt for the height without showing the preview of the operation.

The other options inside the Extrude command can be accessed by right clicking and using the shortcut menu, by using the cursor and then selecting the desired option, or by simply using the command prompt. These options include using the last height of a previous extrusion, taper angle, direction and path.

Let's focus on taper angle today. A positive taper angle will make the extruded faces converge. Once the taper angle is selected, you need to specify a height. The real time preview does not work after adding a taper angle to the operation.

 

So after finishing the command, the results would be the following:

 

If you now click on the extruded model, you will see grips along the vertices of the original profile, and a control at the top of the extrusion. Let's talk about the latter. If you click on this control, you will be able to change the height of the extrusion and have a real time preview. The curious thing is that we can see the preview even if we have used taper angle, even though the preview was not enabled during the creation of the extrusion.

 
 In older versions of AutoCAD, if the taper angle and the height produced a self intersection, the command would fail. After 2007, you can keep dragging the control for the height even up to the point of self intersection, and still get a predictable result. If you select the object again, you will see the extrusion control not on the edge that was defined at the convergence of the faces, but on the height where you dragged it. If you select it again and drag it down, you may recover the top face, if you go down the point of self intersection.

In the next post, we'll see what happens when we edit the vertices in the profile, and when we do some direct manipulation over the model's subobjects.

 
 

Comments

[Shashank]

Good information, but can you specify how to achive similar results with numerical input rather than pull - push?