"normal is ambiguous" - unable to do wire cut

Hi everyone,

does anyone know how do start addressing the problem that’s causing a “curve normal is ambiguous” message that prevents a wirecut from working? All surfaces are joined, I have no naked edges so it should be “good” solid. I need to make a straight, horizontal cut through it but the wirecut just doesn’t work. I tried it another way, by extruding the line where the wire cut was supposed to happen and use the resulting surface as a cutting object with the split command. Here the response was “objects don’t intersect”. I can’t understand this as the objects quite clearly intersect, the cutting surface goes right through my object.
I constructed my solid with clean and methodic steps and didn’t have problems when using Booleans such as union or difference along the way. The cutting line was drawn as a simple straight line. Really don’t know what else to check…
Does anyone have any ideas?
Best regards

If you’re getting the message “objects don’t intersect” from a plane and your object to cut when they clearly intersect visually, there is likely a problem with the object. It may look “good” and even pass check, but there still might be something wrong - or it might be a bug… Only way to know for sure is to post a file with the object…

–Mitch

Thank you Mitch, I have sent the file to the McNeel support team, but not sure if and when they reply. If I don’t get anything I’ll post it here. I have checked for open edges, bad objects, bad surfaces etc. and nothing came up.
I displayed the surfaces normals and everything seems to point into the right direction as well. I have no idea where else to look.
Jeffrey

Well it could very well be a bug… In cases like this, after checking the obvious - bad objects, file tolerances etc. - I start by running Intersect on the cutting plane and the object. If I get no intersection, I try exploding the object, doing a rebuild edges on the exploded surfaces, then rejoining. If the intersect still doesn’t work, I undo the join and run intersect two sets on the cutting plane and the exploded objects. Sometimes one of those will fail, that is the culprit. If all the individual intersections work, then it is the joins that are causing the problem. I then successively start joining stuff until it fails again and that helps find the problem area.

–Mitch

Hi Mitch, thank you very much for your hints, that’s great!. I ran Intersect and it worked completely normally, giving me two continuous intersection curves, exactly where they should be. That unfortunately means I can’t follow your other suggestions…
I have a Rhino evaluation version on my PC at home so I"ll perhaps load the file onto that system and try with Rhino on PC. Should this work then it’s probably a bug in the Mac version, but I tend to think it’s my object.

Jeffrey

If you get two continuous closed intersection curves - assuming it’s supposed to intersect in two places - can you Split the various objects with the intersection curves, then delete the unwanted parts and join? That’s all the Wirecut or Boolean really does…

–Mitch

Many thanks! The object is a shelled/hollow body that needs to be cut into two clamshell parts. I investigated the intersection curves more closely and this is where I noticed some unexpected stuff. As I have raised details on the outer surface and my intended cutting was right next to that detail, fractions of the cutting surface was actually in parallel with that detail, giving me not a single intersection line, but a tiny intersection surface. This messed everything up. I moved the cutting line by 0.005mm out of harms way and bang everything’s working - wirecut and all.
Thanks again, I’ve learned some useful things here!

Jeffrey

Great! Yes, usually a close inspection of the intersection curves will let you figure out where the problem lies…

–Mitch

was there any results on this? am getting the exact same thing and i can do a wire cut