PVA support slicing has weird missing areas in Cura 4.x

[bsaygan 1]

Printer is an ultimaker 3.  Running Cura 4.4 and now 3.6.

 

So I've had a troubleshooting adventure for random stuff in the last few months.  Some of which was hardware wear-and-tear, but generally I had some weird areas of some of my prints where it seemed like I was suffering from some under extrusion (so my troubleshooting tended to focus on that).

 

Today, just because the areas of the prints that would be messed up were so consistent, I looked at the layers.  I thought maybe my 3d model was off, but then I decided to install older (and newer) versions of cura as well as mess with settings.  It seemed that Cura 3.6 sliced my file and provided the PVA supports fine, but in 4.x (4.0 through 4.4), the support on layer 3, would always end up having a weird gap in the same spot - like a hole.  Anyway, this is weird and I think it's a bug, or maybe just the way slicing supports is handled is different in 4.x for some reason.  If I can provide further information for this to resolve in in 4.x I'm more than happy to do so - but see the attached image to see layer 3 sliced of the same model in Cura 3.6 and 4.4 to see what I'm referring to.

 

ALso, I did try to mess with settings in 4.x such as 100% support infill and that hole in layer 3 is still there as an FYI.  I tried other settings but also didn't change anything as it related to that gap.

 

Thanks!

Bobby

 

Edited December 15, 2019 by bsaygan

[burtoogle 513]

Hi, if you could save the project (File -> Save) and then attach the .3mf file to this thread it would be a lot easier to investigate. Thanks.

[bsaygan 1]

I wasn't sure if it mattered for the version of Cura, so I saved both.

Cura3_6_UM3_nes_testhinge.3mf Cura4_4_UM3_nes_testhinge.3mf

[burtoogle 513]

It's related to how the layers are created from the model's polygons. There's a setting called Slicing Tolerance that defaults to "middle". If you set that to "inclusive" that area of support doesn't get removed. However, doing that may also change the shape of the printed object so it may not be a good solution. Alternatively, I found that increasing the initial layer height to 0.3 filled in that missing area. My guess is that the region of the model immediately above where the missing support is must be at a slightly different height than the rest. Hope this helps.

[burtoogle 513]

And a 3rd workaround is to lower the model by 0.01 mm into the build plate.

[bsaygan 1]

Thanks so much I'll try some of those things.  I'll look at the model as well, but just found it weird.  

[burtoogle 513]

One other thing I noticed was that it creates a lot of support on the top surface of the model around the hinge which doesn't actually support anything (looks like a bug to me). Anyway, you can remove that excess support by reducing the Support Horizontal Expansion setting to, say, 1mm.