I’ve been struggling with this keyboard case for a few days and still can’t find a proper solution to that. What I need is a proper fillets with G2 at least (for smooth renderings). I tried several strategies and now I’m totally out of ideas. If there’s anyone willing to help me with it I’d be more than happy.

Another way is to make one of the blends continue and make a cut on the other. Notice that you cannot get full G2 at that transition, that’s as far as I can tell mathematically impossible:

Somehow I did almost perfect blend Of course curvature graph proves it has nothing to do with class A surface but still in rendering and mold milling it’s more than OK.

dear @pascal
isn ’ t there a small part of a sphere missing ?
… and it can be skipped because of tolerances ?

I get the following approach / result with G1 fillets:

after filleting the initial surfaces (black)
with 5mm (brown)
and 1mm (violett)
the violett fillet is extended with a sphere (green)
now i can readjust the red surfaces, to be tangent to that sphere.
which is the condition, for the light blue 1mm fillets to also end in this sphere:

@Tom_P That corner was an XNurbs surface.
To construct that in Rhino without it, this is a possible approach: Starting with a Blendsurface, adding as little sections as possible, and then ‘massage’ these as close as possible using the tangency and curvature handles. The match I’m showing in this video is not perfect, it will need more time, but the closer you can get this in the blendsurface itself, the easier it becomes in the next steps, where MatchSrf is used to further tweak the surface