Unable to Join Surfaces

Hi there, I’m having trouble joining surfaces in Rhino. One of the surfaces was created in Solidworks, saved as and Iges and then brought into Rhino. The other is a 2 rail sweep. "

The project is for masks for Docters and Nurses to wear while treating Covid19 patients. Any help would be much appreciated.


Joel McDavitt

Without a .3dm file of the surfaces which are not joining (strongly prefered) or at least images of the surfaces (better than nothing) the only help I can offer is some general comments about joining. You can post a .3dm file by dragging the file to where you type your post, or by clickin on the vertical arrow above where you type your post.

Probaby the most common cause of not being able to join surfaces in Rhino is when the edges to be joined are not close enough to each other. The general rule is the edges need to be within 2 x absolute tolerance to be joined. CrvDeviation can be used to check the maximum gap between surface edges. Start CrvDeviation and select surface edges when curves are requested. MatchSrf can be used to bring the edge within tolerance of each other.

There is also the brute force solution of JoinEdge which “joins” the surfaces but does not fix the gap - it essentially overrides the tolerance. Only use JoinEdge when you need a to join surfaces and cannot take time to fix them. Be aware that using JoinEdge can cause problems in the future, and fixing the problem at that time is typically a lot more work than fixing it initially.

Hi David,

Thank you so much for your quick response. Very much appreciated. I have not tried MatchSrf yet. I’ll give that a try now.

SV180 - Covid19 T4 - 3M Dual Connector - V2.3dm (1.2 MB)

I would greately appreciate it if you could look at my file and help me out with this.

I used the Patch tool for the middle red surfaces and a 2 rail sweep for the ones on the sides. Quite a few of them don’t seem to be joining. I went back and tried to at least join these surfaces because they are the most simple, but cannot for the life of me figure out why they won’t join:

I created the blue surfaces in Solidworks.

Absolute tolerance is set to 0.001 mm. You might relax it to 0.01 mm.

The blue surfaces join without any problems.

I was able to join the inside and outside surfaces by using MatchSrf with the Refine match option but the edges between top opennings did not join. Fundamental problem is a combination of not enough spans used for the Patch surface and the tight tolerance. Try remaking the Patch surface with twice or three times the number of spans. Then use MatchSrf with Refine match option if needed. (Rebuild won’t solve the problem because the edges are trimmed and MatchSrf does not alter trimmed edges.)

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Wow ok, thank you so much. I’ll give that a try now.

Oh man, after relaxing tolerance to 0.01, the inner and outer 2 rail sweeps joined to the solidworks surface fine. Thank you so much!! Going to work on the middle patch surfaces now. Thanks again.

maybe you can use BlendSrf to make a half and then solve the transition in the middle later:

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Wow that look great. What tool did you use to combine them in the middle? “Adjust surface blend”?

I upped the spans on the patch by 3 times like you suggested and it joined! Gonna try to do the same to the others now. Thanks again!

It worked! Hallaluyaaa! You guys have literally helped to save lives tonight! Thank you so much!!!