Patchy rendering

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  03 March 2013
Patchy rendering

Hi all

I am new to 3DS Max and learning by reverse engineering other people's work. I have a task to render jewellery created from JewelCAD software. The software exports model in DXF format and I can import it into 3DS Max. However, when rendering it I get patchy surface, causing the HDR image reflection to look distorted.

The scene has been downloaded from If I render the model the author has provided in the scene it renders smooth. But when I assign the same material to my model it renders distorted. I understand my model surface isn't correct.

So can someone guide me on how to fix it? I am new so a more detailed help will be useful

See sample rendering output:

See the DXF model file here:
  03 March 2013
It looks like a smoothing problem. I'm going to move this to the Max forum, as it's not a texturing issue.
  03 March 2013
It indeed looks like a smoothing problem.
3ds Max will sometimes import some formats by writing triangles directly and guessing normals/smoothing groups. This can lead to some inconsistencies to you may have to set the correct smoothing groups.

Another possibility is that, if you're using environment mapping, the UV co-ordinates are wrong, and this causes the visual distortion.
  03 March 2013
Applying a Smooth(not Meshsmooth or Turbosmooth) modifier should fix the issue.

Quote: If you're using environment mapping, the UV co-ordinates are wrong, and this causes the visual distortion.
UV coordinates are ignored when using environment mapping.
  03 March 2013
Oh, really? I've yet to work with environment maps. I apologize for my bad information. <_<

Another possibility that I hinted at but didn't fully elaborate on was that the vertices for each face are separate so there's no smoothing groups to joining, thus causing the faceted look.
  03 March 2013
Those unwelded verts are likely what's causing your smoothing errors. Certain file types can get a little wonky when you import them into 3DSMax. I remember dealing with CAD data that would do this from time to time.

Try welding the verts, and assigning everything to the same smoothing group and see if that takes care of it.

If after you try that, you still have hard edges, do an open edge check. Hit the border subobject mode and do a select-all and see if anything is selected. If there's a selection, chances are you have some flipped normals.

A couple other suggestions.

1. Do a reset XForm from the utilities panel.
2. Select all of the faces, and do a detach. This usually cleans out any display errors, and will give you a good idea of the state of the geometry. You can weld verts and flip normals from there.
"The best things in life are either illegal, fattening, or take too long to render."
  03 March 2013
Thumbs up Resolved

Thanks all for some possible routes. I resolved it using Smooth modifier and applying 'Auto Smooth'. TurboSmooth with iterations 2 also works but makes the software extremely slow.
  03 March 2013
Turbosmooth increases the polycount and also changes the topology which may lead to unexpected and unwanted resuls.
There's a reason why I wrote Smooth, not Turbosmooth.
  03 March 2013
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