Creating a rectangular to circular bossing

I have a number places where I need to create bossings for pipes that create a smooth transition from rectangular shapes to circles. The image kind of, sort of shows what I am trying to do. But I need to have a smoother transition. I have tried several different approaches but nothing has satisfied me.Usually the problem is bulging at the corners.

What it looked like I need is to create transitional frames consisting of eight arcs: one at each side and one at each corner.

The radii at the corners go from zero to that of the target radius. The radii at the edges go from infinity to that of the target radius. The problem is how to keep the arcs of the intermediate frames tangent.

Is there any good method that would allow me to adjust the position of one arc such a frame while maintaining the tangency of all the arcs in the frame.

May not be exactly what you are looking for. Standard method for sheet metal work: SquareToCircle.3dm (99.4 KB)

Thx, that is what i had been doing. I need to have the sides curves rather than straight.

Would ‘BlendCrv’ help?

Hi @miano
Here’s how I usually go about this.

HTH, Jakob
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SquareToCircle2.3dm (158.8 KB)
First create one half of each surface.
Top arc is 1/16 of the circle.
Bottom line is 1/2 of the side of square.
Loft between arc and point.
Loft between line and point
MatchSrf the two surfaces

MatchSrf the bottom of the side surface and the line![MatchSrf2|253x500]

Mirror the two surfaces.
ArrayPolar to complete

It appears to me the solution to the problem is to be able to create a conical loft that narrows slightly in the middle. Once the the corner curves are in place, one could generate the side curves.

As shown here, the problem is to get frames that create a smooth loft. This one gets bulges.

Problem Boss.3dm (3.3 MB)