Odd Loft Behavior (Bug?)

Problem Loft 5.3dm (3.2 MB)

In the attached file I have an armor plate that is 12.1" at the top and tapers at knuckles to 1.62". The knuckles are parallel to the base line. However, top edge slopes upwards in two segments linearly.

I created three frames to match the profile. The frames are identical except that the line defining the top facet and back facet increase in length with the upper profile moving with them.

If I do loft with straight sections split at tangets, cap, and merge all faces, I get the mess shown at the top of the figure.

As workaround, I
(1) removed one matching segment from each frame (creating an open polycurve)
(2) Loft with straight sections
(3) Merge all faces.
(4) PlanarSrf in the omitted area.
(5) Join all
(6) Cap

That appears to give the correct answer.

Should Loft be able to figure this out with the closed curve?

File attached.

I’ve read through your description 3 times and am looking at your file.
I do not understand what you’re trying to convey.

The only thing I find messed up is the angle tolerance in your file 0.001 degrees is likely to cause problems.
Try 0.5 or 0.1 degrees.

I have a layer containing three closed curves. If they are lofted they create the mess in the top picture.

If have layer containing the same curves with a segment missing. If loft those, I get the apparently correct surfaces shown in the bottom (after doing planarsrf to fill in the hole.

If I Join the curves on the Separate layer first, then use the Natural option in Loft for the Seam prompt, I’m getting what I think is a good Loft.

Sorry for the delay, Computer has been out of action for nearly two weeks.

The problem is the objective is to create a seam at each change in thickness. You get multiple seams to the left of the center frame. That goes away if lofted with an open curve then filled with a planar surface.

Yeah… if you need to match up each curve segment then I think lofting that top set of varying-length lines separately from the rest will get you what you are after. Point matching is a long-standing and still open request for Loft.