Export to Step, Parasolid, etc.. generates open solids and other errors

Hi everyone,

We are working with a customer that is generating some models using grasshopper for which we are to manufacture on our router. The model that gets generated is being sectioned into interlocking pieces similar to this: T-Rex Dinosaur (Anatomically Correct) - Dinosaurs | MakeCNC.com

Where we run into problems is when we export the file out, some residual information gets passed into the new solid file that makes some of the solid pieces open. Not only that, the errors/artifacts that get translated over are extremely hard to repair if they can be repaired at all. In one instance, my CAM/CAD software sees the open solid, but says it can’t repair it. So, I go to delete the face along the edge in question, and once it’s deleted, more faces appear from the intersecting piece that would be there on a complete assembly. Super odd and I’ve never seen anything like that before with any CAD system I’ve used.

We have the rhino files that are generated and a seat of rhino so that we can inspect and manipulate them if necessary. From what tools I’ve been able to find for analyzing the models, they appear to be intact without error on the rhino side.

I’m not sure what to do here. Our CAM software can import most standard solid formats and I experimented quite heavily with STEP and Parasolid. Our CAM system even imports native rhino files, but they import very poorly and create geometry that seems to be generated with grasshopper to get the basic overall shape of the completed assembly.

Any and all feedback would be greatly appreciated. I would upload parts to show, but we don’t have permission to share these files due to intellectual property/copyright concerns. I hope you understand.


Hello - please send the Rhino geometry (as a Rhino file) that makes an open step file object - post it here, or send to tech@mcneel.com with a link back here in your comments.


@pascal As I mentioned in the original post, I cannot upload the files due to the nature of the design being intellectual property of the owner to which I do not have permission to share. I know it’s hard to give advice in these circumstances, but all I can provide are the errors that I am seeing. Any general guidelines or things I could try is the type of advice I am looking for.

Hello- tech@mcneel.com is not a public forum, in case that helps. If you select the object that goes wrong, in Rhino, and type What and enter - what does the report say?


Hi @Bluish_Inventor
Two things to try:
Run DivideAlongCreases with SplitAtTangents set to yes to break up any surfaces that are tangent.

Run ShrinkTrimmedSrf - it’s my experience that some programs have a hard time dealing with overly complex trimmed surfaces. Make sure that it’s still a valid polysurface afterwards (check for naked edges!).
HTH, Jakob