2.8.0 Bug: Negative Deretraction Extra Length is Ignored When Re-Printing Projects
There is a known bug in 2.8.0, where you can't type in a negative value ( https://github.com/prusa3d/PrusaSlicer/issues/13043 ) in 2.8.0.
I have been fighting with getting good prints with 2.8.0 that used to work just fine. I have increased the temperatures I'm using to get stronger layer adhesion, and figured I just needed to re-tune my retraction settings. I've spent countless hours (and a lot of filament) fighting this battle, and nothing made sense.
I use small amounts of negative Deretraction Extra Length ("DEL") to clean up seams, and have used this successfully for a couple years. A small amount (typically less than -0.05) can make a huge difference. When I loaded in my own files, the negative value appears in the setting window. As long as you leave the minus sign alone, you can edit the value. HOWEVER, it finally dawned on me that if I can't enter a negative value, the software may ignore the minus sign in existing files.
I installed 2.7.4 this morning, and printed the same file that I've been fighting in 2.80. The seams came out perfect (see attached photo).
I don't know what other negative parameters 2.8.0 might be ignoring, but I'm not going to spend time hunting for them. I am going to uninstall 2.8.0, and stick with 2.7.4 for the foreseeable future. I never liked the UI changes they made anyway...
RE: 2.8.0 Bug: Negative Deretraction Extra Length is Ignored When Re-Printing Projects
No it doesn't ignore the minus value. Its a bug with the entering of values. You can copy and paste into a field, just not type it. Depending on the system/keyboard etc it is not limited to just the minus key. Many keys have been reported as not working, number 6, etc The currently open one for all of them is https://github.com/prusa3d/PrusaSlicer/issues/13043
Its a known issue that should be fixed in the 2.8.1 release which is due sometime 'soon-ish'.
Your issue may be this one https://github.com/prusa3d/PrusaSlicer/issues/11914 which is not related to being able to enter a value. Many people have reported it.
RE: 2.8.0 Bug: Negative Deretraction Extra Length is Ignored When Re-Printing Projects
The two prints in the photo are run on my MakerGear M2E printer, so it has nothing to do with Prusa printers.. The only difference between the two is the version of PrusaSlicer. I haven't tried printing the same file in 2.7.4 with the Deretraction set to zero, but I will. If I'm right, the print will be as ugly as the one I get from 2.8.0, which will verify that 2.8.0 is ignoring the negative value. We'll see...
RE: 2.8.0 Bug: Negative Deretraction Extra Length is Ignored When Re-Printing Projects
If you read that issue completely then its not just limited to prusa printers. The devs do seem to be trying to push 'other' causes though. I say this as I also have a Elegoo Neptune 3 Max and I also had big gaps on the seams when slicing with 2.8.
I experimented with this suggestion in there https://github.com/prusa3d/PrusaSlicer/issues/11914#issuecomment-2267579698 and currently have Only retract when crossing perimeters, and I've also turned off Retract on layer change. I have also had to add a Deretraction Extra length of positive 0.1mm to get the seams to come out even remotely like they were before. If I dont Im seeing about a 0.5mm or larger gap. Larger if I use 0.6mm extrusion widths.
Something is off with 2.8 but it isn't the fact you cant enter the numbers as it is USING the values (you can set exaggerated values to use for testing to make it clear that it does).
RE: 2.8.0 Bug: Negative Deretraction Extra Length is Ignored When Re-Printing Projects
I figure there are a couple of possibilities:
1: It ignores negative values completely. I've tried changing the Deretraction several times (always negative), and saw no noticeable effect. If my print with 2.7.4 with Deretraction set to zero comes out as ugly as it does with 2.8.0, then I think that's is what is going on.
2: It ignores the minus sign. It's possible that instead of using -0.04 mm, it is using +0.04. If the test in 2.7.4 with zero doesn't pan out, I will try that. I don't recall it getting worse when I went from -0.02 to -0.04, but that wouldn't usually make a big difference.
One way or another, I will bail after that. 2.8.0 has already cost me enough time & filament, and I need to get some prints done.
RE: 2.8.0 Bug: Negative Deretraction Extra Length is Ignored When Re-Printing Projects
As I said you need to read the whole thing, it looks like its not doing a de-retract at all under some circumstances. So it doesn't matter if the value is positive or negative. The settings suggested in that specific entry are to try and force it to do a deretract. When it does actually do a deretract then it is using the correct value input in the field.
RE: 2.8.0 Bug: Negative Deretraction Extra Length is Ignored When Re-Printing Projects
2.8.0 is definitely doing something screwy. I ran a couple tests with 2.7.4 to see if I could find a de-retraction setting that would duplicate the mess 2.8.0 was making of my prints. A distance of -0.04 mm works well in 2.7.4. I tried a value of zero, in case 2.8.0 was ignoring the negative value completely. That was still much better than 2.8.0. In case 2.8.0 was just ignoring the minus sign, I tried a value of +0.04 mm. That was worse, but not as bad a 2.8.0, and the defects were in different places.
The bottom line is that 2.8.0 is making a mess of prints that work fine in 2.7.4, and I will uninstall 2.8.0.