Lightning infill anomaly

[LindsayPatten 1]

While using Lightning infill there seem to be some extraneous bottom/top surfaces being produced:

I don't see why it is generating the rows on top of the interior surface which is at 45 degrees if that's relevant.  I'm not sure it should be generating "support" for the bottom interior wall but that isn't as strange and might be a good thing.  Is there a setting I need to change?

K1M_Blade100Bottom1.3mf

[Slashee_the_Cow 410]

Everything seems to be working as normal. It's definitely not a lightning thing since those shell sections appear with other infill patterns selected:

The problem is your Top/Bottom > Skin Expand Distance setting - with it set as high as it is, it's generating pieces of skin there because if not for the walls (which take precedence) the gap would be juuuuuust wide enough that skin would be generated to cover that area. As for why it's only happening on a few layers - I'm going to put that down to rounding, since how far over the hole moves isn't going to be exactly the same every layer.

 

So as for your options - and if you want to skip to the good part just scroll down to the bold text - well you can reduce Top/Bottom > Skin Expand Distance since it's also causing things like this unsupported oversized cap:

If I halve it to 0.8mm, there's less skin generated on your 45 degree surface there, but it introduces a problem or two of its own:

You'd need to reduce Top/Bottom > Skin Removal Width to balance it out (at 0.8mm here):

 

But the better fix: Drop Top/Bottom > Maximum Skin Angle for Expansion to... well anything below 90°, because that makes it do it everywhere it thinks it might be necessary. Here it is at 89°:

[LindsayPatten 1]

Thank you very much Slashee!  Changing Maximum Skin Angle for Expansion to 89 seems to fix everything.  As it happens I had to abandon use of Lightning infill as some of the larger relatively flat walls were warping when they didn't have infill to hold them in place.  It worked well when I was printing the models at half size but I guess large areas of thin walls probably can't be expected to stand completely on their own.  At least with ASA which is prone to warping.

 

I wonder if the default value for Maximum Skin Angle for Expansion ought to be 89 by default?  It seems to me that one shouldn't encounter anomalies when using the default values.  I don't see anything unique about my model that it should require changing somewhat obscure slicing parameters in order to make it print cleanly.  As you noted, the issue also occurs with the other infill patterns and I wonder if it isn't occurring for many models without being noticed because it is obscured by the infill.  I may have only noticed it because the Lightning infill provides unobscured views of the interior?

 

Anyway, thanks again for providing a workaround, I doubt that I would ever have been able to figure that out on my own.

[Slashee_the_Cow 410]

9 hours ago, LindsayPatten said:

I wonder if the default value for Maximum Skin Angle for Expansion ought to be 89 by default?  It seems to me that one shouldn't encounter anomalies when using the default values.  I don't see anything unique about my model that it should require changing somewhat obscure slicing parameters in order to make it print cleanly.

There's nothing inherently special about your model, but it just happens to accidentally be the perfect combination of factors to trigger behaviour like this 🙂 It's not something I've seen before (either in my works or while helping on the forums) whereas dropping the default value for Maximum Skin Angle for Expansion to 89° is likely to create unexpected results for more people. 90° ensures all skin gets expanded, so we don't get people wondering why all their skin gets expanded except this little bit at the top of a curve (for example).