Surface transition

I’ve attached a section from an existing model where a fillet failed. I can’t add a fillet to the two areas shown so it’s a really difficult transition for me to get me head around… I’ve tried splitting the fillets in half long ways and blending the surfaces etc.

It’s going to be rendered so needs to be tangent or at least curvature continuous (as it can be!)

Any ideas?


Surface transition.3dm (504.5 KB)

Hi Andy - I guess the key is to make this surface, green, between the two existing reds (FilletSrf, r=.508)

And toss out the planar ‘remnant’ that is right there. There’s more trimming/retrimming to do, and you need to work out what happens at the spherical gap there still.


Hi Andy,

i’ve extended one of the fillets using Sweep1 and the along edge option. Then merged it into one like the red fillet in pascal’s pic above. To get the green fillet in above picture, i’ve just used _FilletSrf, between the larger surface and the red fillet. Then extend and trim with the mirror line…

I was lazy so i mirrored the larger srf (red in my file) to close it.

Surface transition_c.3dm (494.8 KB)


Hi Pascal,

Where does the large red surface come from? I can’t FilletSrf between the two as 0.508 fails… This is where I fell down before. Blending the surfaces doesn’t seem to work but your solution looks like it does.



Hi Clement,

The same goes for your solution, I can’t seem to get the FilletSrf to work at the desired radius, it fails. I’d tried a few different approaches with extending, blending before I posted etc.

Thanks for the help guys, it’s much appreciated.



You can make either fillet to overlap the other fillet with filletSrf,
But in one case (the .508 fillet) you need to untrim and extend the surfaces that have been trimmed back by the failed filleting.

In the enclosed file it shows how either fillet can be made to overlap the other. The green surfaces are the ones that need to be untrimmed and extended so that the .508 fillet will reach. In the other case the .496 fillet reaches so all that has to be done is trim the surfaces.
Surface transitionx.3dm (255.4 KB)

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Ah! Got you, I didn’t untrim it.

I ended up blending the surfaces and sweeping back to the centre of the main curve in order to fudge it.

Thanks for the detail.

Cheers everyone!