The surface trim command is the 3D counterpart of the standard trim command used in 2D drafting, but instead of trimming lines and curves, you will trim surfaces. To start the surface trim command, you can type SURFTRIM (or just use the short version and type SURFT) and then press Enter. Alternatively, the Trim surface tool button is located in the Edit panel on the Home tab in the 3D Basics workspace:

If you are using the 3D Modeling workspace, you can find it in the Edit panel on the Surface tab.

The surface trim command can be used to trim surfaces in a similar way to the 2D trim command as shown in the following example:

1. After starting the surface trim command, select the surface(s) you want to trim and then press Enter to end the selection stage.
2. Select the surface/edges that will be used for cutting and then press Enter to end the selection stage.
3. Just like the 2D trim command, click on the side you want to get trimmed and then press Enter to terminate the command.

The following diagram is an illustration of the previous steps:

In the previous example, a planar surface was used with the trim command, and a surface was used for trimming. The surface trim command will work fine with curved surfaces and with curves as cutting edges, as shown in the following examples:

The trimming edge or surface is not required to be intersecting with the trimmed surface. The surface trim command can project the non-intersecting cutting edge/surface on the trimmed surface, and you can even control the manner of projection using the options that appear on the command bar when using the trim command:

The first option is called Extend. This can be selected by clicking on the option name in the command bar, or by just typing E and then pressing Enter. The Extend option has two settings, Yes and No, and it controls whether to activate the automatic projection of the cutting edge/surface on the trimmed surface.

The second option is called PROjection direction. This can be selected by clicking on the option name in the command bar, or you can just type PRO and then press Enter. This option allows you to choose between different options for the cutting edge projection method on the trimmed surface.

The following diagram is an example of using a non-intersecting cutting surface:

We have learned how to trim surfaces using the trim command. However, AutoCAD allows you to undo the trimming operations executed by the surface trim command using a very specific command for this task, which is called the surface untrim command.