PrusaSlicer 2.7.0 weird Variable Layer Height bug
Ello,
recently I was Slicing a new model/design that had a screw thread in the middle of it and to make it as smooth or at least functional as possible I always Variable layer height.... thing, such that the screw threads would print in a higher quality and work better.
Though some times when I set the variable layer height as I wanted in PrusaSlicer, suddenly the layer above it gets split in two or even the topmost layer. It's a bit hard to explain how it looks like but I have provided screenshots below (I also provided the .3mf file of the part that I used).
And here is how it should look like (removing the Variable Layer height)
Once I completely removed the Variable Layer Height setting or just lowered it, the issue was fixed. Though this gave the compromise of having the thread less detailed at the top.
I hope that this issue could be fixed or at least given a solution to (retaining the thread quality). Personally I dislike the way Prusa made the Variable Layer Height adjustable, could've made it more concrete by making it the same as with the colour changes.
RE: PrusaSlicer 2.7.0 weird Variable Layer Height bug
Your top surface isn't flat/parallel. So at some layer heights all the vertexes fall into a particular layer and at other layer heights the verts on one side fall into one layer and the others fall into a different layer.
This is quite a common thing and expected. Flatten the model surface. Also there is no 3mf attached so I cant see if the bottom of the model is perfectly flat to the bed too. Often it wont be and will be very very slightly off. Sometimes uisng place to bed tool will align everything. Other times the model needs fixing if it actually not parallel.
You have to zip up files to attach them. As the edit window is very short it is best to check immediately after posting to see that it was properly attached.
RE:
Sorry for not providing the 3mf file, I accidentally pressed the submit button and completely forgot about it. I also did Notice just now that the part is not flat at the bottom. Though still, I had this before with a model that was perfectly flat at the top & bottom and it also did the same.
RE: PrusaSlicer 2.7.0 weird Variable Layer Height bug
Though still, I had this before with a model that was perfectly flat at the top & bottom and it also did the same.
As Neophyl said. I'd put any amount of money on the top and bottom surface not being perfectly parallel. They may be perfectly flat but not parallel. I've seen tiny angles such 0.0000001 come out of not properly constraining a line or surface in cad software, resulting in those steps you're seeing.
RE: PrusaSlicer 2.7.0 weird Variable Layer Height bug
Hmm, mkay
Thanks for the ideas, I'll keep watching this issue, maybe it is just a reaaaallly slight misalignment
RE: PrusaSlicer 2.7.0 weird Variable Layer Height bug
Here's an example from someone I was trying to help with the other day, with exactly the same issue. Based on layer height chosen, s/he saw a step in what was supposed to be a flat top surface. After loading the model into Fusion, it became apparent that the two surfaces while flat were not parallel to each other. 
RE: PrusaSlicer 2.7.0 weird Variable Layer Height bug
I also experimented myself and I wondered if this could be because of Fusions "Refinement" option when exporting it to PrusaSlicer.
RE: PrusaSlicer 2.7.0 weird Variable Layer Height bug
Not to say that's not possible. I have just never seen this myself and I use Fusion every day.