How to best fillet this corner

Hi there!

I’m currently working on a model that has a corner like this:

When trying to fillet with 3 edges I get this:

And With all connecting Edges I get this:

I have a fair amount of Inventor/Solidworks/Blender experience, but am fairly new to Rhino so not sure how to get the fillet to work correctly.

you should post a file.
(save as → choose save small option , drag and drop into the post-edit window) where you re typing)
Rhino is not the best Fillet-CAD-Package.

using _filletEdge it is important, that you choose all 6 edges in one go.

i gave a similar typology a try and get a result:
(i expected only the rectangular / left version to work - but both worked…)

post the file or at least the 6 surfaces so we can have a look at it. kind regards -tom


Hey Tom!

Appreciate the response, your examples were exactly how I imagined it would. Attached I have a portion of my model, although if this doesn’t help I can just post the full thing. I assume it has to be something with the way I’ve set up the mesh, I just can’t figure out what that is…

Example.3dm (397.7 KB)

Dear @Hans_Hartle
hard to guess - the corner (1) you posted works with
_filletEdge R0.2

Hans_fillet_00.3dm (3.8 MB)

you can explode + join
single parts of the more complex construction to find the badly behaving corner.

also trying with smaller radius
analysing the bad result of _filletEdge
might help to find the error.


I’m going to attach the complete solid object as although _filletEdge R0.2, and _filletEdge R0.3 work on the corner when it’s separated, each of those radii break the the mesh (I’ve even tried R0.05).

Here’s with R0.2:


I would expect that the fillet would connect those points and not leave naked edges. I then thought this might mean that I needed to add all edges in the same _filletEdge command, and tested by adding the next few neighbors but the results just got worse :joy:


Is my mesh too complex and/or poorly designed for the fillet edge command?

Example2.3dm (1.2 MB)

(not mesh - polysurface, which consist of trimmed, joined nurbs-surfaces)

some details are not possible for filletEdge

but lets see what pascal is typing…

Hi Hans - one thing to consider is to make your elements too deep and then trim them on the inside of the ring all with an exact cylinder, and avoid these not-quite-clean intersections:



Hey Pascal!

Thanks for the response! That was originally my intent to do before starting the fillet process, but my Boolean difference of the exact cylinder from the ring failed at that spot. I’m assuming for the same reason of the I fought for a long time with the Sweep 1 Rail command to get cross to work, and naively continued to add on thinking I could fix this later.

@Tom_P and @pascal is the best course of action here to fix and align those intersections?

Tom - Ah, sorry for using the wrong classification there.

Hi Hans - I would think about overbuilding then cutting inside and outside with a clean exact surface -


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Alright! I’ll give this a shot and report back on how this goes.

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there is _extendSrf - nice to adapt the surfaces…
if you want to follow pascals suggestion:
build the extruded surfaces as pascal suggested
_explode the original object
_hide stuff you need later
_delete stuff you don t need anymore
_extendSrf to get a nice intersection
_trim _bool* _createSolid and other commands to get a new solid…

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Also keep in mind that the width of the “legs” are only 1mm, so how visible will this be?

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Hi everyone, thanks for all of your help!

I spent the better part of yesterday evening and this morning working through your suggestions!

After creating the two surfaces and cutting out the shapes I ended up with something that was very similar to my original design:


I was able to successfully fillet nearly every edge:

However the fillets seem to fail at mesh edges (naked edges highlighted in pink).
Naked Edges
Naked Edges2

Do I need to rebuild the model again to remove these intermediary edges, or is there an easy fix? I tried a fair number of things ranging from splitting the model along the surface planes, filleting, and then rejoining, to blending surfaces with little success.

I guess:
those open edges / gaps are the result of the neighbouring edges are not tangent.
marked red for an example:
and even if they are tangent _filletEdge sometimes does not find a missing “cross” fillet. … i search an older post about this and add a link.

if you 3d print the object you can generate a mesh
→ export selected as stl…

if you want to make it correct:
_matchSrf to get tangent relation
or _filletEdge with a much bigger radius first.
build missing Fillets with
_extractSrf _untrim _trim _join
(which might end up in a lot of work)

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Hi Hans - it looks like maybe it is failing here

which suggests that your curve - the one you extruded to get the top image base surfaces - is not quite tangent there. Can you post that curve? I think folowing @Tom_P 's recommandation is probably fine to fix up this model but we can probably learn somerthing for the future by dissecting that curve.


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Hey @Tom_P and @pascal,

Thanks for your continued help here. I’ve been spinning my wheels a bit trying to get this to work. I’ve tried a fair number of approaches / fixes so trying to keep this comment organized and scoped.

  1. Unfortunately, although I have too many saves to count, I don’t have one that still has the original curve I used to extrude on.

    • I tried rebuilding the curve (I’ll attach this one) so that I could send your way, and so to that I could add in the connecting sections:
  2. I’m going to also attach here a file containing (I tried to organize everything in layers):

    • My Original Model
    • The Model Built in the post above before/after fillet edges
    • My Newly generated Outline

I’m a bit lost as to how to get back to my original shape while having the edges filleted :confused:
Again I appreciate the help, let me know if I can provide better files / things that I’ve tried.

RingCutout.3dm (5.7 MB)

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Hi Hans - I see - I’ll see if I can make something that makes sense to you.
@Hans_Hartle - my suggestion is to start with something like this:

i.e. over-built, so that you can then carefully trim everything back with all the intersecting surfaces -

RingCutout_PG.3dm (7.1 MB)


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Hi Pascal,

A huge thanks for walking me through the steps. I was doing the inverse(taking the ring cross section, extruding it, and then cutting from the cross section with all of the shapes made by projecting the edges of the original model. This worked okay but wasn’t able to get the height differential you got in the middle! I’m assuming I can do the same thing with the holders for the side stone.

I’m still seeing that when filleting the edges on the model you sent me that it has the same problems as my original on these edges:

I’m assuming this one is because there are technically two separate faces, but I haven’t been able to get them joined as one:

But this one I’m not sure at all, is the angle to sharp?

I assume that adding in my side stone holder will result in these same fillet errors. Is the only way to fix these corners by manually editing merging the surfaces?


I went down the path trying to manually fix the corners but have been able to get a great result. I also am seeing tons of render tearing along the edges (that I did not adjust) of the fillets around the problematic corners.