With Swarf milling, the tool aligns itself with the ruling direction of the surface. As the toolpath moves from one surface to another, there can be a change in the ruling direction and therefore the tool axis. This is called fanning.
Enter the minimum distance over which fanning can occur. The fanning distance is measured as the smallest movement on either surface edge (or the distance the closest part of the tool is to the opposite part of the surface before fanning starts). The actual fanning distance may be larger than the Minimum fanning value specified, to prevent the toolpath from gouging.
Ruling direction of surface 1
Ruling direction of surface 2
Fanning distance