Boolean Difference and Subsequent Fillet creates Naked Edges only in IGES Export

Boolean difference of these closed polysurfaces create naked edges only revealed in IGES export. Fillets of nearby edges also creates a similar error. Please help. I can’t figure out why these solid objects without errors in Rhino 6 create naked edges when they interact as an IGES export at tolerance of 0.001 mm.

Test.igs (857.6 KB) Test.3dm (5.0 MB)

Hello - file tolerance is .01. If you export at a tolerance smaller than the modeling tolerance, nothing is gained - try this: in the original file, set the tolerance to .001. Explode your object and RebuildEdges (defaults) then Join and check for nakeds…


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Changed tolerance in Rhino 6 to 0.001. Exploded object. RebuildEdges (33 surfaces completed). Joined. Now I have a ton of naked edges.

Yes, exactly - if you want the object to hold together at .001 tolerance it needs to be built at that tolerance or smaller. Exporting to iges and asking for .001 tolerance does not actually change anything in the geometry itself - it is only as accurate as it is. If you import your iges into a file that has .01 tolerance, then it should close up with no nakeds, but in a file with .001 tolerance, you’ll see the nakeds, if you see what I mean.


I think you’re getting hung up on the tolerances, which don’t seem to have anything to do with this issue. I rebuilt the entire model at 0.01 in Rhino 6 and the objects were all solid and error free. And then exported the IGES also at 0.01 mm tolerance and the issue with naked edges still occurred.

Hello - start a new model from a ‘Large Objects’’ mm template. Import your iges file and Join. You get a solid, no nakeds.

Now start a new model from a Small Objects mm file and import the same iges file and Join. Nakeds.

The difference between the default ‘Large objects’ and Small Objects’ template files is the tolerance is .01 in the former and .001 in the latter.


you should work with a tighter tolerance (normally I use 0.001 mm).
in any case try to avoid iges in favor of step.

no one is using iges anymore, it’s 2021!
happy new year.