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STP geometries exporting with issues

tony_459tony_459 Member Posts: 206 ✭✭✭
edited July 2020 in Using Onshape
Some STP geometries are exporting with major faults. Some aren't even complete. Others are missing surfaces, or have surfaces that the original didn't have. And still others export with rough polygon surfaces instead of the smooth curved surfaces I went to pains to give them. The issues show up in various STP viewers, so I'm guessing they stem not from the viewers themselves but from the way the STP files were produced.
Here's an example. In Onshape:
In STP viewer 1:
In STP viewer 2:
In STP viewer 3 (yes, same part!):
In STP viewer 4 (also same part):

Not all geometries are affected, but many are. One of the worst cases I resolved by changing my modeling approach---replacing a surface revolve + thicken with a solid revolve + shell---so it seems at least some of the issues are related to how the geometries were modeled?

Here's the more severe case mentioned just above... As modeled in Onshape:
In STP viewer 1:
In STP viewer 2:

In STP viewer 3:
In STP viewer 4:

... And to show that changing my modeling approach fixed this one STP file---though only in one of the STP viewers---here it is, in STP viewer 1:

If I import the STP files back into Onshape, the geometries show up fine without issues.

Has anyone else run into this issue? Why are my STP files not matching my Onshape geometries? Is there something I can do to fix the broken geometries, or at least to prevent them in the future? Thanks!


  • tony_459tony_459 Member Posts: 206 ✭✭✭
    edited July 2020
    So I looked into where in the feature history the first STP file shown above breaks... Here's that geometry (in Onshape) again:

    Feature 1: Revolving a half circle into a solid sphere.

    Feature 2: Splitting the near end with a plane.

    Feature 3: Splitting the far end with a plane.

    Feature 4: Extruding a round hole through the truncated sphere.

    Not pointing fingers, just detailing an issue that I'm sure affects or will affect others... Would be nice to get consistently usable STP files... If it's an issue with my modeling approach, it would be nice to know that too. I hate to put numbers on things for which I don't have numbers, but if I had to guess, I'd say one in twenty STP geometries has issues. Thanks!
  • NeilCookeNeilCooke Moderator, Onshape Employees Posts: 4,802
    What do they look like when imported back into Onshape? That is the true test. 
    Director, Technical Services, EMEA 
  • tony_459tony_459 Member Posts: 206 ✭✭✭
    They look good, Neil... It's just that I need these geometries in third-party tools, and there, as you can see, some STP geometries are pretty broken... Luckily, most geometries are fine, and those that are broken are mostly hidden out of view, but still... I'll need to find a way to fix them...
  • NeilCookeNeilCooke Moderator, Onshape Employees Posts: 4,802
    But is it just the fault of the viewer? Can you try importing into FreeCAD or similar?
    Director, Technical Services, EMEA 
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