Need help modeling convex triangle

Hello! I am trying to recreated digitally some existing ornaments for a friend’s balcony and I am very stuck with one part and maybe someone could help!
Basically the shape is an 8-sided dome that starts from a 4-sided base (an octagon emerging from a cube)

My trouble here is that on the corners, I am supposed to connect the point on the edge of the cube to the dome shape, creating a triangular convex surface (?)

This is what I have now:

this is how the thing has to look like:

I tried using loft, sweep, sweep point to curve
I’m not very pro on rhino, so I guess I am definitely missing something

If someone could give me a light would be amazing!
Thank you all!

I will drop the file as well
Ornament4.3dm (4.1 MB)

It’s a little late for me, so the quality is poor, but this might be a start…

I think that just adding a filleted section would be problematic because the part you would run nearly coplaner to the part that is there.


So, the part underneath needed to be removed, or really the affected face needs to be rebuilt.
What I did was:

I copied everything.

I exploded the finial.

I created 2 curves by copying the side edges of the finial section I moved out.

Using your height reference line, I split the lines I created, using the point option.

I curve-matched the curves of the lines you intended to be the fillet edges, to the copied edge curves.

I joined the fillet curves to the edge curves.

I used EdgeSrf to create the long surface from the result edge curves.
(Sweeping and lofting likely won’t work.)

For each side, I used the remaining curves to edge curve the end cap.

There still may be gotchas when assembling it, but this may work, though you have to be more careful than I am, while trying to stay awake.


Also, it looks like in the photo, that the main sides of this thing look kind of like a pointy oval.


If you have one of these swoopy faces, you can also make it wider, and then array polar, and then use them to trim each other and make a solid. Surfaces can overlap while creating a solid, as long as the result would be airtight, and it’s cool to watch.


You can also make a subtraction tool using one of these swoopy faces and a few more surfaces, and then subtract the tool from the post, or whathave you, and keep rotating it between subtractions, or perhaps just do a boolean 2 objects using the surface and the solid post.

Hey Brenda!
Thank you so much for holding up awake and help me out!
There were some gotchas indeed, but what you did really helped me out on a way to start this thing!

thanks thanks

Hello - I think the simplest way to do this is to flatten the edge curves in the axis of the surface:

then extrude the curve:

and then trim with the original edge curves:


Or explode the edge curves and simply loft across.


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