For three or four surfaces, if you choose **Automatic as the curve to indicate that the system should automatically calculate the curve then the following restrictions apply:
the fillet surfaces must extend to where they intersect with the other fillet surfaces. This figure shows an example of surfaces that do not intersect.
If the surfaces are not a FeatureCAM-created fillet (either not a fillet at all, or an imported surface), the automatic corner boundary calculation may fail. In these cases it is better to specify the curve-on-surface for that particular surface.
FeatureCAM attempts to find a closed loop across the three or four surfaces by intersecting the rail curve boundaries of each fillet with the other fillet’s rail curves. This figure shows rail curves.
Therefore, if any of the curves on surfaces are specified, they must intersect with these rail curves of the fillet surfaces where a curve on a surface is not supplied.
If a fourth surface is supplied, it is usually not a fillet surface. For these surfaces you must supply a curve on the fourth surface. Remember that the curve supplied must be on the fourth surface and should be tangent to the rail curves or the neighboring fillets.
If the automatic calculation fails, try a bigger tolerance, supplying more curves on the surfaces or extending the fillet surfaces so that they intersect. Sometimes it is helpful to recreate the fillet surfaces with a tigher tolerance or a variable arc step.
General restrictions
With only two surfaces, you must indicate curves on each surface to connect.
For three sided cases, if there is a natural pole
as in this figure , it is best to but the fillet surface that is furthest
from the pole at the first surface. 