Or another method for making a type of groove is to use boolean difference with one profile curve to cut a chunk out and then fillet those edges:











- Michael

@HansChristian

Sorry, I think I have made more steps and forget explaining.
It's a reverse thinking from result to conditions.
The first question was to do a "middle curve" and my solution is based on doing an Iso curve from a surface.
This surface is done with initial conditions given, the "squared tubular cutting".

To do an iso curve, I need a surface and only one surface, not a joined surface.
To have an only one surface constuction, lofting need to have "soft curves" (no angular point on the curves).
So I use a "reconstruct curve" with many points to have these two soft curves.

The middle curve is not an ofset, it's an iso (V iso I think).
Iso permit to have the center curve of the surface even if the distance between the 2 initial curves is not regular.

Next I use the iso curve to do the sweeping.



But I think, the initial question was to do a circular border.
The easier way for this (I think it, but perhaps I'm wrong) was the first method explained, with a "Curve/Project" to have a curve and to sweep a circle with this projected curve.
This method is in my file too.
I used "reconstructcurve", but it's optional here.

Hi Michael

First of all. Im sorry for the late reply. I had a very busy day yesterday and today.


<Were those meant to be planar cross-section surfaces? Those are the ones you don't have in your .3dm file. But it sounds like there is a Grasshopper method to generate those for you automatically?

Yes excactly you don't have those surfaces. But by slicing a solid tube into small pieces you could find the cross section midpoints for each and then connect them all.




<Ok, but to get a tube like that another approach that would be simpler could be to project just one curve onto your solid and then sweep with that rather than cutting out a channel with 2 curves:

<For example, just one profile curve:


Thank you very much for your reply. The suggestion of projecting the curve alle around the solid was a brilliant idea and much easier. I think thats the solution :-).

I really appreciate all the response and kindness here.

Hi Michael
That's an interesting option too with filleting. I have to experiment with that also. Thanks for taking all the time to help!

Hi Phiro

Thanks for that detailed explanation. Im sorry the answer took so long. I have to try it myself and dig into it. I will try making that isocurve and so on and report back :-). Thanks.