Attach Two Subdiv Surfaces
Maya 2012 Tutorial
How to Connect Two Subdiv Objects in Maya
Using this modeling technique, you can create your model as a series of Subdiv sections. The sections are then joined to for one continuous surface. In this example we are starting with an existing Subdiv Surface. For information on creating a Subdiv Surface, see topic; Converting Polygons to Subdiv.
Add a Subdiv object to the workspace. For this exercise you could also use a Subdiv Primitive Plane (Create > Subdiv Primitive > Plane).
Duplicate your object (Edit > Duplicate) and move (w key) the duplicate next to the original.
Select both objects and choose Subdiv Surfaces > Attach (with options) from the Surfaces menu set.
In the options, increase the Threshold if the edges of the two objects are slightly separated. Deselect the Keep Originals if you have no use for the original objects.