A common scenario in 3D modeling using surfaces is to have two separate surfaces and you want to connect them using a smooth curved surface. The Blend surface command is just the tool for the job. To start the blend surface command, you can type SURFBLEND (or just use the short version and type SURFB) and then press Enter. Alternatively, the Blend surface tool button is located in the Create panel on the Home tab in the 3D Basics workspace, as shown in the following diagram, and if you are using the 3D Modeling workspace, you can find it in the Create panel on the Surface tab, as shown here:

The blend surface command can be used to create a surface connecting the edges of two existing surfaces. These edges can be open or closed and you can control the blending curve shape as shown in the following example:

1. After starting the blend surface command, select the edge of the first surface, and then press Enter to end the selection stage.
2. Select the edge of the second surface, and then press Enter to end the selection stage.
3. You will be prompted to change either the continuity, the bulge magnitude, or you can simply press Enter to create the surface and terminate the command.

The following diagram is an illustration of the previous steps:

The following diagram shows other examples of using the blend curve command:

If you select the surface, you will find two small arrows at the two ends of the surface. If you click on one of them, it will open the continuity options for this side of the blending surface. There are three options that control how the surfaces flow to one another, as shown in the following diagram. You can also access all these options during the creation of the blending curve by selecting the continuity option that appears just after the command terminates:

Another method for controlling the shape of the blending surface at the meeting point with the originating surfaces is to use the Bulge option. Once you select it, you enter a value between 0 and 1, with 0 representing no curvature and 1 maximum curvature:

The blend surface command has an option called Chain that can be used to quickly select a loop of tangent-connected edges. This option will appear in the command bar right after you initiate the command. To activate it, click on the option name in the command bar or you can type CH and then press Enter. Now, if you select an edge, all the tangent-connected edges will be automatically selected, as shown in the following diagram:

We have now learned how to smoothly blend two separate surfaces. Let's now learn how to seal a hole in an existing surface using the patch command.