A modeling tool is activated in a 3D modeling application executing on a multi-touch device. A visual representation of a grid system tool is displayed in an active modeling plane and has three separate regions that determine the type of operation to be performed. An existing 3D form is displayed on the tool. A starting touch event of a gesture is received over the existing 3D form within one of the regions. As the gesture is received in the computer, the 3D form may be dynamically extended by adding 3D geometry to the 3D form (thereby adding faces to the 3D form). Alternatively, the 3D form may be scaled (i.e., if the starting touch event occurs over a visual scale grip. Alternatively, if the gesture consists of two taps, a bridge may be created joining the two tapped locations.