Unwanted support material

[kbuckler 0]

Cura 3.2.0

Why do I get unwanted support material around my part and on top of part geometry? There is no overhang geometry around my part or in the middle of my part where the support material is being generated.

[DidierKlein 729]

probably horizontal expansion

[nallath 1,124]

Horizontal expansion is indeed the setting to fix it, but it doesn't explain why we do it. The issue that the horizontal expansion is trying to fix is that printing very thin PVA supports tends to fail; Either due to support being knocked over or PVA degrading in the nozzle (as not enough material is extruded). The only way to fix it is to ensure that enough material is extruded per layer. As we optimised for reliability, it resulted in too much PVA in quite a few cases.

[gr5 2,210]

In normal view were there red areas there?  If so play with the support angle - sometimes that fixes it.  Cura definitely gets confused on what areas need support and what don't.  I'm not sure why but I think it has to do with the "surface normal" in STL files.  Many CAD packages don't set that value properly and this messes up the algorithm that tries to figure out where support is needed.  Possibly it might help to run the model through a mesh repairer like the free one at netfabb here:

https://service.netfabb.com/login.php