You can re-center the pivot rotation center to any point on an object you wish by selecting any vertex or group of vertices of the object you're trying to work on in edit mode, then press the "." (the period or dot button) on the numberpad of your keyboard. This will focus the pivot of the scene around the selected vertex or vertices, allowing you to rotate around that given point of your model with the middle mouse button, and make it much more convenient for modeling up close on smaller objects in a scene.

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