Introduction
The Surface Workbench provides tools to create and modify simple NURBS surfaces. These tools have a similar functionality to the 
Part Builder tool when the Face from edges option is used. However, unlike that tool, the tools of the Surface Workbench are parametric and provide additional options. In this respect, the tools in this workbench are similar to 
PartDesign AdditiveLoft and 
PartDesign AdditivePipe.
Some of the features provided are:
- Creation of surfaces from boundary edges.
- Alignment of the curvature from neighboring faces.
- Constraining of surfaces to additional curves and vertices.
- Extension of faces.
- A mesh can be used as a template to create spline curves on its surface.
Usage
The Surface Workbench intends to create faces with shapes, which is not possible to do with the standard tools in other workbenches.
Surface created with sketches placed in datum planes with the tools of the PartDesign Workbench
The Surface Workbench integrates with other workbenches of FreeCAD. The above example was created from 
Sketches placed on 
PartDesign Datum planes in the 
PartDesign Workbench. The design can be fully parametric if all datum planes and sketches are defined accordingly. In most cases it is sufficient to draw a closed sketch to define the boundary of a face, and then use different options to further modify its shape.
The generated surface cannot be placed inside a 
PartDesign Body. However, the generated surface can be contained inside a 
Std Part together with the associated PartDesign Body that holds the datum planes and sketches. The non-parametric Part Builder tool can then be used in order to create a shell and finally a solid.
Tools
Filling: fills a series of boundary curves with a surface.
Fill Boundary Curves: creates a surface from two, three or four boundary edges.
Sections: creates a surface from edges that represent transversal sections of surface.
Extend Face: extrapolates the surface at the boundaries with its local U parameter and V parameter.
Curve on Mesh: creates approximated spline segments on top of a selected mesh.
Blend Curve: creates a Bezier curve between two edges, with desired continuity.
Esta página foi obtida de https://wiki.freecad.org/Surface_Workbench