Help with intersection failure

Hi everyone,

I have two objects which appear to be intersecting (plan view from the right shows overlap along entire length). I need to trim one back to the other. Boolean Difference doesn’t work. There are no bad objects in the scene. So I tried Intersect. The intersection is found on the inside of the object, Even after exploding into separate surfaces, the intersection is not correct. Splitting or trimming doesn’t work either.

Based on other posts on here, I’ve tried increasing and decreasing tolerances, but to no avail.

Does anyone have any suggestions? Please see attached. Thanks!


no intersection.3dm (230.8 KB)

At this point it is then hard to say at what tolerance the objects were made. Changing tolerances ‘in mid air’ is generally not a good idea.

I ran RebuildEdges on the objecs after exploding them. This caused the large face to move to where the intersection curves are calculated. Deleting that face and using the edges of the side surfaces of the triangular object to make a new face shows that these edges do not make a planar surface with the current file tolerances.

You probably have some input constraints that are not in the file - I would advice to remake that triangular object and try again. (FWIW, based on what I see in that file, here is a version with a new triangular object and the other trimmed back to it… Uploading… - hmmm… doesn’t seem to want to upload at this point…)

@Wim, @cbass - you can get an idea about this from the info provided by What - the triangular object has edge tolerances up to .09, well outside the file tolerance - possibly edited by direct subobject editing of edges or faces?


Thanks to you both for your replies.

I’ve never had a need for “what” until now! I am working with files created by other people, so I have to deal with what I have. I will speak with the designers to ensure usable tolerances for the future. In the interim, I have removed the offending surface and rebuilt it using corner points. Booleans do work after the surface is redefined and that is what really matters for this project. It doesn’t cap, but this should be fine for CNC machining.

The surface attached to the non-planar edges was created in Solidworks as part of a shell and then imported into Rhino (using IGES or maybe ParaSolids). Certainly translating between formats can’t help the situation. Keeping things native in Rhino throughout our workflow may help minimize these problems in the future…

In any case, thanks for helping me out!