Fillet Exercise / Challenge - Feedback and Practice

Dear everybody, dear commutity, dear mc neel

This is a test / exam I asked my students (4th (overall) Semester (2nd Semester with Rhino), Product-Design) to check, whether they see the underlaying geometry and, if they can model this object in Rhino V7 Mac and PC.
I gave them 120 minutes to model it.
I just designed this handle only for the purpose of this test:

handle_2022.pdf (705.3 KB)

I did not find a pure solid, boolean**, _FilletEdge Solution.
My approach uses surfaces, _filletSrf, _trim, _join
and optional some workflows shown here:

I don t care about, if the technical drawing full-fills the standard requirements - this is why i also attach a mesh-version of the solution - for better understanding of the geometry:
handle_2022_MeshReferenzreduced.3dm (522.3 KB)
please let s skip this aspect in this topic

I would love to invite everybody to try to model this object. Whether it is for learning / training / or just for a rainy evening.

But I would especially ask the more professional people and other teachers to give a feedback.

  • is this a nice and realistic object to test filleting ? (in therms of curriculum for product design)
  • feel free to ask your students to model this object - but please keep the reference, and feedback how successful they have been.
  • this object shows some of Rhino’s fillet limitations, how do you handle this in your classes ?
    tell the students to use another program ? learn them advanced workflows - that are not necessary in other programms ? teach them workarrounds like - just use patch, use 14.9mm instead of 15.0mm, pipe-trim + sweep2, …
  • i hope some of this examples pushes the rhino-Developers to improve the fillet-commands - i like the idea of posting challenges - at some aspects in VSR end of life it is discussed, how to interact between community - mcneel - the developers, maybe some kind of challenges is a nice approach.

some of the people i would love to read a comments from:
@pascal you are a fan of pure sphere based / ball-like fillets i know ;-D
@theoutside i know you re teaching as well
@Rhino_Bulgaria as you are a very active user, and i love your post in the VSR topic
@Mark_Landsaat as you are doing those nice details and fillets on your bicycle parts
@Cadworx because you answered my post in the VSR topic

and let s limit the topic to Rhino other software might give faster results.


this is a cool test. As as add on, give them a new drawing of this part with a few things changed and have them disassemble and change the part to make the changes.

This will simulate a client change or iterative markup.

very realistic test.

Pipe trim and blend is a great technique to teach as it’s a very good way to force a fillet in an area where the automatic tools may fail.

we always want cases that fail so we can get them in front of devs… .files with repeatable failures are developer gold-

maybe more the ore deposit (had to google translate this)
i will post some “fillet fails” fail later in this topic… looking forward what others say.
thanks for your comment

I don’t mind making other types of transitions, on the contrary - it’s just that when a complaint is that a Rhino filleting tool fails, it’s best, IMHO, to provide a solution that makes ‘true arc’ fillets where possible.

I’ll take a look.

@Tom_P - from what I can see this is a fine exercise - the only thing I found was that to my remaining braincells at least, the detail around the screwhole was not fully defined in the drawing.

I did it this way:


ok i post a first version. based on (a wrong) approaches of my students. i ll call this version “v01 maximum pain”

forget everything in the layer “Version01_Max_Pain”
but the curves will get you a faster start… the mesh reference is also in this part

one first version including a wrong apporach, but all info and initial curves to start fast and fail soon with boolean and fillet…
handle_2022_02_maxPain_tec_draw.3dm (5.1 MB)

Huh ! :sweat:

Tried by ( what I thought was ) the simplest plain old way: surfaces and FilletSrf.
But looks like Rhino 6 was not so eager to build a couple of those fillets … :wink:
Had to use some little ‘trick’ to make Rhino change its mind … :smile:

Pretty complex exercise IMO.

Thanks for sharing !

dear @emilio
thanks for giving it a try.
i think as soon as fillets get complex (i agree on your opinion about the exercise) it is not obvious how “different brains” (users) break down a “complex body”.
I think there are different “barriers” (i love the german “stolperstein”) and it would be great if those special cases - that pop up with this object - could be mostly covered by the filletEdge / filletSrf algorithm. would you mind share your “simplest plain old way” and the “trick to make Rhino change its mind”. just to collect the developers “gold” as kyle called it.

yep i agree.

tech draw

these details in the (attempt to do a fast ) tech-drawing - i hoped show what s going on there…

not showing all fillets

for simpler geometry i love the approach to show the geometry in solidworks style, without the last fillet in the planar view, only in the perspective.
but then - which of the steps should i take - all will give some wrong information because the solution is only possible with _filletSrf … (maybe setPt …) _trim _join Workflow

this first version will show somehow a “legal” way without any fillet - and with some additional surfaces that will fall away (but will kill rhino s fillet algorithm)

one step further - not bad - but this state shows some lost surfaces - that are needed for the final version

this last version - maybe the best - only the R4 fillet missing - not very realistic exercise as it already requires a full cad model - - including the first R4 - telling the necessary hierarchy to solve the problem…

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Hi Tom,

I think the same user may come up with different solutions for the same problem when working on different models, for example.

Hmmm … I had already deleted the auxiliary objects :confused: :slight_smile:.
But I have quickly drawn them again … more or less :wink: .

Nothing strange there.
The starting surfaces are actually the faces of the solids you posted ( I only drew a cylinder and a sphere instead of the upper box ) then I simply used FilletSrf and Trim.

The tricks are simply using (possibly enlarged) original (untrimmed) surface to help Rhino with fillets that start at the edge of the surface.
And a couple of cylinders to help building fillets that would end on a surface with the same curvature radius as the fillet radius.

Auxiliary surfs are green in the file.
The red fillets are those that required an auxiliary cylinder in order to be built.

Anyway I wouldn’t complain about these problems.
IMO they are borderline cases.
I’m fine with having to help Rhino a little for things like these. :slight_smile: .

handel.3dm (240.3 KB)

thanks for sharing your approach - yes those auxiliary cylinders / surfaces are one (nicer) approach to get those more difficult fillets.
But for a rhino newbie (my students) - it s hard to understand where / when this help is needed. And for a Creo or Solidworks-Modeller - this looks unusual / un-necessary as well.

Took me about an hour. Some of the fillets are better made as revolves or extrusions.
handlex.3dm (2.1 MB)


Dear Jim
yes you are right

give faster / nicer / better results for some of the surfaces. - but only if you see / recognise these geometries. Do you think the object is to complex / has to many special cases for a test - or did you like it ? kind regards -tom

Yeah, I believe that Rhino is not easy lo learn. And even harder to teach.
I would not be able to identify any base concept or schema to follow in order to know how to start drawing things.
You also have to know what different commands can do and cannot do.
It requires quite o bit of experience.
Very flexible, but also very anarchist about tools, features, commands, UI, roadmap …
I guess that is the price to pay for not having to pay too much (sorry for the mismatch :wink: ).
SW and Creo cost about 20 times as much as Rhino. :confused:
On the other side FreeCAD is … well, free. :grinning:
We’ll see … :slight_smile:

The one thing that strikes me as strange is that while surely a technical exercise for executing fillets, the example you choose would serve better as how to not do filleting from an aesthetics/design point of view:
Lots of pointy surfaces, no apparent “readable” hierarchy of surfaces and over all, no offence, an ugly end result, to put it plainly.
This is the result I would expect an engineer to come up with.

Please don’t take this the wrong way it is not meant to be an insult.
I am just a bit baffled as to why teach design students with an example that seems aesthetically rather unpleasant.

Your example highlights some of the bugs in Rhino surface creation tools. In this case filletSrf command. The Rhino user has to learn to work around these bugs because after decades the one thing we know for sure is that McNeel is not interested in fixing them so it up to the users to be smarter than the developers. Recognizing alternative ways to create the same surface is a basic Rhino survival skill.

I liked it a lot. The part is actually very elegant in its simplicity.

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Dear Norbert @norbert_geelen
yes this exercise is limited to some simple planar extrusion, revolve and fillet - Surfaces - which is more a design/shape-vocabulary of the engineers world. But half of the students really struggle in seeing already those simple geometry in a more complex object - and the test is focusing on this as well. The object is about teaching tools, not about design / shape - i discuss those aspects on their individual design-projects - but then it is not a comparable test, and it is nothing I can do in a small timeframe, and fit s for different levels.
But I can see your points of critique from a design-perspective - thanks.
by the way - this was the initial inspiration of this object - but the transitions are more complex and not pure fillets:

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Hi Tom:
As I said, no offence and obviously I can’t say anything about your curriculum or what is best for your students.
The way you are striving to give them the best possible modeling challenge tells me they are in good hands.

Hi Tom,

Your exercise is a perfect example of how many/most engineers go about applying fillets. Solve it with what your choice of cad package can do, rather than create how the design should be from an aesthetic point of view. Using rolling ball fillets that end in points never turn out good, ever. Your initial inspiration is a good example not to use rolling ball, or fillets at all. Defining the fillet boundaries is much more important than a fillet value. Rhino is easy to learn but like with any tool it’s about how to use it. Anyone who can hold a brush can paint but it takes more to make a great painting.

Dear Eric @ericg - thanks for your comment. I also don t like

from a design point of view - but still i think it s an important workflow students have to see / to learn. And as already discussed with Norbert - this object is really more a collection of fillet-Workflows then a design-masterpiece… have a nice day - kind regards -tom

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From a fillet workflow i think it’s important to teach students never to accept fillets ending in points, regardless of aesthetics. And only use your example of how not to go about.