FilletSrf fails to produce 12 mm radius

[Rhino_Bulgaria (Bobi)]

The FilletSrf tool fails to produce a 12 mm radius fillet in this particular model. If I join the surfaces and run the FilletEdge command instead, it does the job just fine. Why the superior FilletSrf tool is incapable to make it happen? Obviously, there must be some “under-the-hood” calculations due to the inclined shape of the two side surfaces. Should we expect improvements in this regard in Rhino 9?

FilletSrf fails to produce 12 mm radius.3dm (148.2 KB)

[Tom_P]

nice catch.

my guess:
at arround R=9.27 (green result) there is no initial unextended Surfaces for _filletSrf.
the red R=12 Surfaces is beyond the scope of _FilletSrf.

my observation - alchemistic guess:
_filletEdge always uses extended surfaces under the hood

apply _filletEdge (left) and _filletSrf (right) to the same Surfaces.
_explode
_untrimAll
you see the extended surface of filletEdge, while filletSrf is resulting in a minimum untrimmed version:

There are rumors that @menno is working on improved fillet features… ;-D

kind regards - tom

[Rhino_Bulgaria (Bobi)]

Thank you for the insight and time to comment on the matter! I have the same observations and honestly I mostly use the great script by @jim posted here:

Filleting Tangent Surfaces

For those Rhino users who use the FilletSrf command and would like the process to be a little less tedious here is a Python script that will make strings of fillets that expands FilletSrf capability when filleting tangent surfaces: FilsrfEX.py (40.1 KB) This script works the same as the filletsrf command - just pick 2 surfaces that you want to connect by a fillet. The difference is the script will continue to make all the tangent fillets connected to the first fillet until it runs out of tangen…

Sadly, since it relies on the FilletSrf tool, it also fails to produce fillets in certain situations where the operation requires an extended fillet surface to meet the criteria for building it.

[jim]

@Tom_P

you see the extended surface of filletEdge, while filletSrf is resulting in a minimum untrimmed version:

There is really no correct untrimmed 12mm fillet that connects those 2 surfaces.
Perhaps the extend option in filletsrf should make an extended fillet, but with extend turned off the fillet made must always be untrimmed and filletsrf is doing the correct thing.

You can’t make a correct untrimmed fillet much bigger than 9 mm that connects those surfaces.

@Rhino_Bulgaria

I mostly use the great script by @jim

The script is for tangent surfaces. When there are tangent surface connected to those surfaces the script will do it right while filletedge will not.
Here is an example:
tangentSrfs.3dm (2.4 MB)

FilletEdge tries to make one fillet for each edge but the resulting fillets don’t match and don’t connect to each other.

[menno (Menno Deij - van Rijswijk)]

I have logged this issue here RH-85335

[Rhino_Bulgaria (Bobi)]

Thank you!