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AutoCAD Tutorial

AutoCAD 3D Modeling: Trim and Extend

July 31, 2003

The TRIM and EXTEND commands are not only used in 2D drawings but also applicable to Wireframe models. In this tutorial you will draw a 3D polyline and use TRIM and EXTEND in 3D space.

If you are not familiar with Wireframe models, read the following tutorials.

AutoCAD 3D Modeling: Wireframe Models, Part 1
AutoCAD 3D Modeling: Wireframe Models, Part 2
AutoCAD 3D Modeling: Wireframe Models, Part 3


  • This tutorial is designed for AutoCAD 2004 though might be applicable for other releases.
  • In this tutorial user entries are in boldface.
  • The 8 symbol represents pressing Enter.

1. Download the following files:

Note: If you are using AutoCAD 2002 or an earlier release download:

2. Open the drawing in AutoCAD.


Note: To learn how to load an application into AutoCAD read the following article:
Loading Applications into AutoCAD 2002

4. Invoke SPIRAL.

5. Set the values as shown in Figure 1. Make sure to deselect Solid Model option.

Figure 1

6. Click OK. A 3D polyline will be created [Figure 2].

Figure 2

7. Change the view to SE Isometric [Figure 3].

Note: To learn more on 3D views read the following tutorial:
AutoCAD 3D Modeling: 3D Views

Figure 3

8. Draw a line along Z axis. The start point of the line is origin and the length is equal to 30 units [Figure 4].

Figure 4

9. Invoke EXTEND.

10. Select 3D polyline as the boundary edge, and then press Enter to exit the boundary edge selection mode.

11. Click the top end of the line to extend. The line will not be extended as it really does not intersect with the polyline.

12. Select the Project option and set the projection mode to View:

Select object to extend or shift-select to trim or [Project/Edge/Undo]: p8
Enter a projection option [None/Ucs/View] <None>:

13. Now click the top end of the line to extend it [Figure 5].

Figure 5

14. While pressing Shift key click on the bottom end of the line to trim it [Figure 6].

Figure 6

15. Press Enter to exit the command.

16. Change the view. As shown in figure 7 the boundary/cutting edge was only valid in the previous view.

Figure 7

About the Author

Alireza Parsai is the founder of cadpanel.com. He is a mechanical engineer with more than 12 years experience with AutoCAD. Alireza is an Autodesk Authorized Author, the AutoCAD consultant for Al Khawarizmi Institute, a contributing editor for Augiworld magazine, a writer for CAD Digest, an instructor for AUGI Training Program, and an elected speaker for Autodesk University 2002. He has written 7 books in Farsi, 3 booklets in English, and more than 30 articles for different magazines and newsletters. You can reach him at alireza.parsai@cadpanel.com or visit his website www.cadpanel.com

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