Surface fillet gives varying diameter

Hi can anyone explain why when I create a surface fillet on a solid cylinder I’m getting a result that has a varying diameter as shown in the image.

The filleted edge on cylinder on the right was created using the Variable radius fillet tool and the cylinder one the left with the fillet surface tool. This was done in Rhino 6 WIP.

In Rhino 5 both the Variable Radius Fillet and the Surface fillet tools result in a cylinder with varying diameters.


Hi Jon - if by ‘Variable radius fillet tool’ you mean FilletEdge, then yeah,this tool was cleaned up, as I recall, in V6 make cleaner output on circular edges. The less exactly circular edges are refit, and not the simplified ‘special case’ circles you expect…


Yes the FilletEdge tool (sorry it says Variable Radius Fillet when I hover over the icon).

So this is a bug then? Or is there something I can do in Rhino 5 to correct this? I can’t work in Rhino 6 as the display is too slow.


In Rhino 5 you will have to draw an arc and revolve that. It’s become second nature for me to do that and so I hadn’t noticed yet that rhino 6 does that right. I will have to try to remember that. :older_man:

Even though you are getting the radius reading that are not exact, the fillet is well within the tolerance. So no, it is not really a bug. It is less than desirable though. Please note that the radius command give the local radius of curvature and does not take the entire curve into account. If you compare the two circles using CrvDeviation, you will see that they are very close together. Much closer than the deviation that you are seeing in the local radius of curvature. In the attached file Fillet.3dm (42.5 KB)
I’ve filleted using both FilletSrf and FilletEdge using V6. Red is from FilletSrf. While the radius around the circular rail on the planar face varies between 34.15 and 34.2, the actual deviation between the exact circle and the red fit curve is 0.000006. The same should be true when comparing the V5 results to the exact FilletEdge result in V6.

Thanks Chuck. The CrvDeviation command is a new one for me :slight_smile:
I know the difference in diameters are very small so wasn’t too concerned but just wanted to make sure I was missing something.