Prusa Slicer printing features that don't exist
I've noticed that on a model which I have imported into Prusa Slicer, it prints features which do not exist. In the 3D Editor view, they clearly aren't there, but once the model is sliced they appear.
I can't post the entire model picture as it's a propitiatory model, but I've attached snips of both views to show this issue. Take a look at the right hand top of the pictures, in the 3D viewer the entire top of the model is flush, but when sliced there are two nubs that appear and the front edge is recessed two print layers compared to the rest of the model. While I'm sure that this is an issue with the original design of the 3D model, it seems that the 3D Editor recognises the extrusions and cuts correctly, but the slicer does not.
Has anyone else seen this before, or does anyone have a solution?
RE: Prusa Slicer printing features that don't exist
Hard to offer solid advice without a .3MF file to look at, but I think what you are seeing here is not 'PrusaSlicer printing features that don't exist', but rather 'PrusaSlicer leaving out parts that do exist'!
It looks as if the walls between the nubs (that should be there) are too thin to be printed with the settings that you have. Try turning on 'Detect thin walls' in the Print Settings (you need to be in Advanced mode to see that) to see if it makes a difference. If that does not help then you may need to adjust your model.
Others may have more suggestions.
Cheers,
Tim
RE: Prusa Slicer printing features that don't exist
Thanks for your input Tim. You're right that these features do exist in the 3D model created for the item, but an extrude cut has been used to "delete" them. The 3D Model Viewer in Prusa Slicer correctly identifies that they shouldn't exist, but then the Slicer will slice them as if they do. It's as if when the slice happens, it ignores the extrude cut from the 3D model.
What's confusing me is that the 3D Model Viewer in the same Prusa software manages it correctly, but upon the slice, it's wrong.
RE: Prusa Slicer printing features that don't exist
I guess I didn't make my point very well!
From what I can see, your model has thicker walls at the corners. PrusaSlicer has no trouble with those and they are the nubs that you are seeing. The height of those above the flat section looks consistent with the model.
Between the corners, the wall thickness seems to be tapering as the height increases. It is hard to tell from the image, but it looks to be just a single line on the last layer that is shown between the 'nubs'. Beyond that, the wall simply becomes too thin for PrusaSlicer to generate a tool-path for the extrusion (it can't extrude half a line - it is either a line or no-line), and so it just leaves those parts out of the slice.
This is not a defect in PrusaSlicer, it is just one of the limitations that apply when going from an idealised model of what you would like to get, to what the printer is actually able to print.
Try slicing the model using the PrusaSlicer preset for the 0.25mm nozzle size. You will probably see that this fills in some or all of the missing sections.
Try the 'Detect thin walls' setting as I indicated above to see if that helps.
I can't offer much more without having a .3MF file to look at.
Cheers
Tim
RE: Prusa Slicer printing features that don't exist
As Tim said, classic case of walls to thin to print. When you look at the model in the viewer it looks fine, sure, because it shows you the surfaces of the model. But then the slicer goes to work and realizes it can't produce the thin walls and you end up with holes. Detect thin walls sometimes helps but may also create other artifacts. Best to redesign with more wall thickness.
Formerly known on this forum as @fuchsr -- until all hell broke loose with the forum software...
RE: Prusa Slicer printing features that don't exist
Hey Tim, fuchsr - you're absolutely correct. Checking for thin walls showed that the issue was exactly like you'd suggested.
By pure coincidence, the 3D model design had an artifact which caused the internal fillet to create a nub after being applied, which had been removed using an extrude cut. The way that the model sliced creating the nubs looked identical to the 3D model file before the extrude cut, which is what caused the confusion. After changing the model to have a thicker wall and double-checking using the Detect Thin Walls feature, the model is slicing and printing perfectly.
Thanks again for your help 👍