Blend help

I’m having trouble creating a smooth blend between the lavender wall panel and the yellow inset panel in this model
Blend Question.3dm (496.6 KB)
. I would like a large radius blend similar to the one between the wall and the window.

Thanks in advance.


Hi Dennis - if you can make your insset shapes like this:

trimmed to one another, I think the susequent operations like BlendEdge will have a better chance of success. I’d use ‘DistanceBetweenRails’ as the rail type here.

Hm - but your surfaces are tangent, or nearly, along the edges most of the way around so the Blendedge tools may fail… it may be a Pipe and trim or OffsetCrvOnSrf job to get the rails you need.

Something like this, maybe - the insets are all clearly and consistently angled to the outer face - not all the same but each one constant. Then some hamd buyilding, I just did one ‘quadrant’ as an example.
Blend Question_PG.3dm (416.3 KB)


Thanks Pascal but I don’t see how you trimmed both surfaces against each other when the upper surface stops in the middle of the surface below it. What am I missing?

I strongly recommend you to simplify your basic surfaces right from the beginning, in order to keep the control points count at minumum, because all the secondary surfaces you add later will increase their complexity, hence the chances for errors. Using simple surfaces will also provide you with a greater control over the modification of your surfaces.

For example, you may want to extract your larger main surface and apply the ! _RemoveMultiKnot command. You will notice that it will remove a lot of unnecessary control points. However, keep in mind that in very rare occasions this command could make the surface worse as it removes some knots that the program “thinks” are unnecessary, but sometimes some random knot may be crucial for the general shape of the surface. Usually that command does very minor visual changes to the surface’s structure while being able to make it much simpler and easier to edit.

Similar command that simplifies a surface, but makes it considerably more smooth and with evenly distributed control points, is ! _RebuildUV. It’s main strength is that it lets you modify and existing surface only in one direction (you can flip it through the Command line options) while keeping the opposite direction intact.

I also recommend you to use the ! _EdgeContinuity tool that was introduced in Rhino 7. It will give you a better idea about the edge continuity and gap between adjacent surfaces.

Recently I used to crease similar shapes for a project, so if you want you may take a look at it and see if it could be helpful for you to try some of these techniques. They are not the best, but still worked perfectly fine for the purpose of CNC-milling a plug from the model.


Thanks again Pascal. I’ve had better success with those surfaces but I could still use some tips on blends as shown in the attached file. I may have approached this badly.

Blend Question2 002.3dm (255.7 KB)

Hi Dennis - I think I’d do something like this, starting with your file -

White and Cyan are BlendSrfs, with the points on the UI moved around apprpriately, the green is a Loft between the edge with MatchSrf but could be another blend surface.

Blend Question_PG.3dm (416.3 KB)


Just a question. Would the interior two edges not have a fillet of some kind? If it could, then a ball corner would work . —-Mark

Thanks again Pascal. I’ll give that a try next.

How did you create the curved corner in the blue surface?

ReplaceEdge > SelectCurve > Pick the edge of the corner piece. However, I previously split the long edges so that the edges to be replaced were just the short ones making the corner of your original trim.


I don’t see how this creates a curved corner.

See if this helps:


Ah, I see. The problem though is that the 2 surfaces I want to form the curve between are in essence a section of a spherical surface, so they curve in two directions. I’m not quite sure how to create a filleted corner there.

Hi Dennis -Use MatchSrf > CurveOnSurface=On, to pull that edge down onto your sphere then use this trick if the edge is a hard corner - or just build everything, untrim your hole and retrim with all the new surface edges.


Thanks for you help Pascal. I was able to replace the corner. The pull command is a great tip!! I couldn’t get the Replace Corner command to work but was able to make a surface using edge curves.