Why are fillets so bad?

I use Rhino mostly for grasshopper but had a recent project that was to generate marketing images so I decided to model everything in Rhino. Is there a reason why fillets are so bad in Rhino? In every other cad package I use a fillet can be used like a design tool to drive geometry, but in Rhino anything beyond the most basic of fillets seems to fail most of the time.

We’re already at V.8 of this software so I’m assuming there’s a reason fillets behave so differently in Rhino vs. other cad software?

So here’s two basic pieces of geometry:
test-block.stp (39.9 KB)

In Creo applying a R20 fillet to the cylinder and R10 to the other object:

In Fusion360 applying a R20 fillet to the cylinder and R10 to the other object:

In Rhino applying a R20 fillet to the cylinder and R10 to the other object:


On the part with the cylinder, Rhino fails to create a fillet once the radius is larger than the distance to the rounded square edge. On the screenshots from Creo and Fusion you can see how the vertical surfaces of the bottom part are extended upwards so they form an intersection with the fillet. Rhino obviously does not extend the surfaces. I think it has to do with the fact that Rhino is more of a surface modeling tool and not a solid modeler like the other CAD packages you mentioned.


I was always under the impression that the difference between surface and solid modelling is somewhat arbitrary - in the end they’re both dealing with geometry in similar ways but just presenting it differently to the user.

Which still begs the question: Why can’t a surface modelling tool like Rhino handle those radii?


Hi @Tom_P could you add this to your post where you collect fillet failures?
Apologize me I can’t find it now

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No worries.


Because fillets is most of what “solid modeling” is, that’s what you’re paying for, if they don’t work there’s nothing the user can do while you can work around anything in Rhino, and with parametrics it should be easier to “know” what strategy to use.

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If they don’t work in a solid modeller then I’d still build the fillet with curves, surfaces, sweeps etc. to get what I want, but most of the time I’m happy with what a standard fillet provides. In Rhino it’s almost always the long way round of building by hand something that, very often - I don’t need in extreme detail - I just need a decent looking fillet to do a quick render.


Don’t build fillets manually with sweeps, just FilletSrf everything. It’s how I do virtually ALL fillets these days, turning your model into a nice solid for FilletEdge is a waste of time. Just place base surfaces, start adding fillet surfaces, the desired result will just ‘pop out.’


What makes you think Rhino’s surface modelling tools cannot handle those radii? Sure, it may take a couple minutes longer to create the exact same geometry in Rhino, but please don’t try to gaslight everyone into believing something can’t be done just because you are unwilling or unable to do it.


It’s highly possible, but McNeel would need to commit developer resources to see it through.


I was very clearly talking about the fillet tool. I didn’t say you can’t create those fillets another way - obviously you can. Lol @ gaslighting.


Nah “gaslighting” is fair. You’re trying to apply solid modeling workflow to surface modeling and throwing your hands up like waaaaa why isn’t it the saaaame???


Where did i rant? I’m asking why it’s so bad / different compared to solid modellers. I’m curious about the underlying difference.


We told you. Because fillets is ALL SOLID MODELERS DO. There are more resources spent on that than Rhino’s entire development team, maybe the entire company. That’s what you’re paying 3X or 10X the price for, the automatic handling more fillet cases.

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I know which of the Rhino fillet tools you were talking about.
I was talking about using the fillet tools in Rhino of which you seem to have no knowledge.

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Not the case anymore. Plasticity cost way less than Rhino and uses the parasolid kernel to do its fillets. And i think MoI3d (also way cheaper than Rhino) uses the ACIS kernel for its fillets.


added here:


Both cases are known shortcomings in Rhino’s filleting system. For v9 we’re hoping to improve the situation.


It would be great to see V9 focus on improving basic surfacing tools all around. The fact that there are plug-in developers filling in the gaps (Cyberstack, Xnurbs) should speak volumes as to what’s missing in Rhino. Don’t get me wrong, the recent additions in V7 (sub-d) and V8 (Shrinkwrap) are great, but the majority of Rhino users would benefit from improvements that are found in the aforementioned plug-ins. I know we would.


:joy: :sob: :sweat_smile: Let’s figure it out :smiley:

I think some devs should tell us straight up like “here’s why…” :melting_face:

k, but why can’t Rhino just extend them anyways? :slightly_smiling_face:

I think it’s mostly due to the lack of parametrics, lack of nurbs volumes, and deficiencies in nurbs non-volumes.

:face_with_hand_over_mouth: :smiling_face:

… back in my day, solid modelers were barely doing surfaces, besides CATIA. I wonder what they’re like these days. Rhino should probably think about picking up the pace, or might get left in the dust. :grimacing:

I disagree. A nice solid is paramount. Fillets are a luxury, and not necessarily what’s needed.

Ultimately, grinders, sand paper, and post op polishing buffing is what the real world uses to make “fillets” :joy:

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