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Merge ribs' end issue


New member
Hi everyone! I'm currently modelating a custom nut with a section that has an outward thread on CATIA V5, however, while trying to create this thread using the command "Rib" I'm getting the following error when I select the option "Merge ribs' end ":

"Topological Operators: impossible relimitiation on the main part. - Change the specifications"

This error is only appearing when I am working with outward threads of any size, while with inward threads I am having no issue at all. I was wondering what could be causing this problem or another method I could use to create a thread with merged ends please.




New member
Hi Bouta! Thank you for your reply. What I'm trying to achieve with the option "Merge Rib Ends" its to create a pointed shape for the nut outward thread's leading edge (which I will then finish by applying an Edge Fillet Definition). On the screenshot you can see the inward thread I have created using this option showing the result I want to achieve for the outward thread:

Inward thread:

Inward thread leading edge.jpg

Outward thread:

Outward thread leading edge.jpg


New member
Ok, so it's easy, imagine that you cut the guide in your inward thread - merge rib ends extrapolates that guide by tangence - so it just adds a straight line which goes into the solid - that's why it closes. Meanwhile an extrapolated helix guide in an outward thread will just shoot into space - so it has no chance of "sinking" into the body. You need to either bend the curve downwards at the end or create that profile with a sweep and close it with "Close Surface". Merge Rib Ends definitely won't work here.