Why won't this geometry boolean difference or trim?

I’ve been trying for quite some time. I’m not a beginner, but for the life of me I can’t figure out what’s wrong with this geometry.

BDF.3dm (189.7 KB)

Rhino has a problem finding a complete closed intersection between the two objects, probably because of near-tangent surface intersections…

Thanks for the quick reply. I had imported a .dwg moulding profile for this. I figured perhaps that was the problem so redrew it in Rhino, extruded and now it booleans fine. How do I find those problems so I don’t waste this much time again? What command would find the problem in the original closed curve or eventual extrusion?

I don’t know what you might use to detect problems with the original curves. If splits, trims or Boolean operations fail, always run the Intersect command between the parts and inspect the result. The open spots will show you where the problem is.

In your case, it appears that two of the curves are not 100% tangent (otherwise the circled joint point below would be on the red dashed line), but I do not know if that is indeed the problem.

Edit: and the answer is nope, I fixed the tangency problem, extruded new profiles and intersected them and still the same problem.

BDF-AttemptedFix.3dm (2.6 MB)

Thanks for the suggestions. I fought with that for an hour before I redrew the original closed curve. Hopefully I’ll know how to catch it when this next happens.

The intersection is problematic as soon as the three selected control points are beyond the orange lines.

One way to solve the problem would be to change the curve so it looks like the green curve on the screenshot. Or trim with a line or plane, delete everything which isn’t needed and join the rest.

What is the result supposed to look like?

Basically, I have an entire catalog of .dwg moulding profiles provided by a vendor. Some are poorly drawn and I often redo them. This was the first time I had boolean problems. I thought it weird since Rhino said the curve was closed. I tried everything I knew such as sectioning an extrusion for a new and definitely planar curve, but that did not work either. I’ll be more diligent with verifying the profile next time. Thanks all.


is able to handle this kind of profiles
even around a rectangle

an alternative might be, to trim with a 45-degree curve…

to bring everything together:
delete one face (that does not follow the Profile
→ closed polysurfae

as @3dsynergy wrote below - it is also possible to use
_shear (45 degree)
to get some nice shape curves in the corner - then
_loft (straight sections)

(left: sweep1 )
(right: shear + loft )
(see curves / surfaces at the right)

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Hi @CalypsoArt and all,

This is a problem that hasn’t been addressed for over a decade now. When I earlier requested that McNeel craft a proper molding tool around the release of V3 I was ignored yet the man hours fixing what the developers refuse to make better even when they know the solution is really astounding.

First I was lucky that Miko showed me the proper way to do these moldings.
Which is to…
Shear your profiles first to the desired miter angle in most cases a 45 and negative 45 degree angle,
Then you place these sheared profiles at the corners and use loft with straight sections. This produces wonderful clean geometry. Unlike sweep one which produces those nasty extra overlap surfaces which on complex Gothic styles is really a bear to clean up. If you accidentally mesh these sweep one shapes without the clean up steps you end up with those nasty corner surfaces. In many cases mergeallcoplanar faces doesn’t work on them.

McNeel should change the sweep one code or add to it a miter molding command that does the shearing of profiles and placement automatically derived from the sweep profile for the sheared shapes and the placement of them on the sweep one rail.

That’s not the end of it. I have to do gutters, try shelling or offsetting even a simple molding shape like a cymarecta and you get constant errors and you have to result to a whole different strategy to model the same shape but with thickness. Argh it should be simple it should be sweep one, shell your done but no it actually is a can of worms. I just did a cymarecta gutter around an octagon type shape with unequal sides and Rhino was not able to add thickness I had to resort to a whole other modeling strategy to achieve that.