Maximum distance within tolerance, unable to join,why?

The maximum distance between the edges of two surfaces is within the tolerance range, less than 0.001. Why can’t they be combined? I’ve been thinking about it for a few days and hope to get some help. Thank you
test (5).3dm (45.7 KB)

Looks like a problems with the edges of the large surface.

RebuildEdges the larger surface. Then Join

I have rebuilt the edges, and before the reconstruction, the maximum distance between the edges of the surfaces was greater than 0.001. What do you think is the problem with the edges?

The model was created in another software and then imported. Does it have anything to do with the external import?

Hi @chenjiajin,

Try retrimming the larger surface (DupBorder, UntrimAll, Trim).

test fixed.3dm (155.4 KB)

– Dale

Very likely.

RebuildEdges worked for me and is simpler.

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Thank you very much, this operation is work.。 I also want to further understand the fundamental reasons why, even though the maximum distance is within the tolerance range, they cannot be combined。I can’t find any reasons why they cannot be combined. Could you enlighten me?