# Angular to circular bossing transition

I need to create a bossing that goes from angled to circular as somewhat illustrated here. The transition frames come from plans. I have done a loft among all but the angled frame.

How might creates a surface that makes this transition?

Bossing problem.3dm (3.1 MB)

What is your tolerance for the surface edges ? I tried lofting and adding a 0.05 radius curve to the angular corners, then increased the control points to 100 and the loft was very close. You can’t avoid a kink at the corners, other method is to sweep two lines taking mid points from the last curved profile in the bend and mid way, make up that final section with four surfaces. Very accurate but not a smooth transition.

I’m not a power user so more elegant suggestions may be offered.

The curves are not parralel to each other, is this also intentional ?

First consider the geometry before thinking about what Rhino commands to use.

Two alternatives for a blend from the surface with continuous curvature to the polyline with corners:

1. The blend surface has creases which wash out between the polyline and the edge of the surface. These creases will have position continuity, G0, but not tangency continuity, G1. Away from the creases the blend surface can be curvature continuous, G2.

2. Triangular blend surfaces from the polyline corners to the edge of the surface. Fill surfaces will also be needed which can have tangency curvature, G1, with the triangular sufaces…

The choice depends on the design intent. The first method has creases but elsewhere curvature continuous, the second has radius of curvature becoming very small and then zero near the corners of the triangular surfaces, and is not curvature continuous elsewhere…

Blend surfaces with creases: Bossing problem creases DC.3dm (270.3 KB)

Polysurface exploded. MergeSrf used to create a single surface. This simplifies next steps.

Guide curves created using BlendCrv with point and edges options. Curvature continuity to surface.

Sweep2 with polycurve and edge of surface as rails, guide curves as sections. Curvature continuity with surface.

Thanks for the responses, I will check them out when I get home. In regard to the tolerance, I use 0.001" I may have not set them when I copied to the sample file.

HOWEVER, I only need close tolerances at the ends where other things will mate up. The frames during the transition are mere guides.

With a 90° corner, there are two options (G0 or G1). With a radius, there are two options (G1 or G2). With the G1 options, you can fabricate the part from sheet metal. They are developable surfaces. The corners are part of a cone.

Squaring the Circle.3dm (146.9 KB)

Blend with triangles: Bossing problem triangles DC.3dm (443.1 KB)

it appears lofting actually works with your curves straight out of the box when you use option tight. you can also merge those surfaces into one, just be careful if you want to offset this surface. if its just a skin to close an object then this should not be any problem. i included a slightly smoothed version, for a even softer transition you might want to include a 2nd circular profile with option loose.

Bossing problem-2.3dm (3.4 MB)