Prusa Slicer First Layer Height Bug  

RE: Prusa Slicer First Layer Height Bug

I've done a lot of scaling in Plicer/Slicer, and never run into a problem like you've described.  ZIP and upload your STL and AMF of your configuration.  Perhaps there's something weird in your settings?

RE: Prusa Slicer First Layer Height Bug

The problem is not scaling inside Plicer. This works fine. The problem occurs when you change the dimension outside of Plicer and update the Model in Plicer with the context menu.

Models: Testcube

Setting are unchanged: "0.20mm Quality MK3"

RE: Prusa Slicer First Layer Height Bug

So, after you re-size your test cube in Fusion 360 and save the STL, do you go into Slicer and delete the old model before loading the new one?  You really should.  That forces Slicer to start over with slicing the new model.  It's really a different part now - whether or not you saved it under a different file name.  I think the problem is that "right click - reload from disk" step.  Just keep it simple:  delete the previous model from your slicer screen and load the newly created STL as if it were brand new (because it is).  The procedure is just the same as if you were changing from Benchy to Adalinda.

RE: Prusa Slicer First Layer Height Bug

Its not about if I should use "reload from disk" or not. I would like to do it, because it results in a faster Workflow, but I can't.

It is a bug, that should be fixed. Or the functions should be removed unitl it is working. Especially because this can crash Plicer completly or damage your Printer because it generates faulty G-Code.

RE: Prusa Slicer First Layer Height Bug

OK, following your workflow I was able to duplicate your results (to the point of seeing that the first layer becomes 0.8mm thick; I didn't try to print this).

I suppose that the feature to "reload from disk" might be intended to help you out if you did some modifications to the part within PrusaSlicer, such as varying the layer height and you then want to "undo" your modifications and start over.  It makes some sense because I note that the Edit menu in PrusaSlicer doesn't have an "Undo" entry.  However, this "reload from disk" evidently ASSUMES that the STL file you are reloading is the same file as you originally loaded.

Honestly, a safer workflow for you would be to give your modified part in Fusion360 a new name - at least for the STL file -  ("gizmo.stl" ->"gizmoV1.stl") and then delete and reload the part in PrusaSlicer.  It really doesn't take but a couple of seconds to do that, and then you know exactly where you are.  It will even show the version (new file name) in the descriptor box on the right of the PS screen.

I have to agree with you that PrusaSlicer shouldn't allow this "reload from file" error to happen, so in that sense it's a bug.  It wouldn't be practical for PS to examine the entire STL file to look for changes, but maybe the program could at least check for the "last saved date/time" and give you an error message if you are trying to "reload" a file that is no longer the same file.  You could submit this as an "Issue" to the software developers at https://github.com/prusa3d/PrusaSlicer/issues

RE: Prusa Slicer First Layer Height Bug

I can't reproduce the error - but then I don't have Fusion 360. But simply renaming the 24mm cube to 25mm before reload should accomplish the same effect.

I'm thinking whatever is happening is related to another "characteristic" of Plicer: it likes to retain part offsets. I think this is by design.  So reloading a smaller cube Plicer tries to maintain world position and adds 0.5 mm to the part Z.  Since Plicer also won't allow parts to be below the bed, it forces the minimal value to the old 0.2 layer one plus the 0.5 offset.  And gets to 0.8 simply by rounding somewhere.

Interesting artifact of an odd workflow - but I'm not convinced it is a flaw.   But submitting a bug report will at least ask the question in the right forum.

RE: Prusa Slicer First Layer Height Bug

I don't have Fusion 360 either.  The bug does not depend on the CAD system used to generate the STL.  I saved the STL for a 25mm cube from my CAD program (Alibre) and then loaded that STL into PrusaSlicer.  Then I modified the file in Alibre to 24mm tall, and saved it again under the same file name (which, by the way demanded that I confirm that I want to overwrite an existing file).  Then I tried to "reload" the cube in PS.

The bug arises strictly from PrusaSlicer trying to "reload" an STL file that has been changed. 

One could argue that this is not the intended workflow, and no one should ever expect to succeed "reloading" a file that is not the same as the original, but one can also make the case that an unorthodox workflow should be impossible by design - especially when the results can be so catastrophic.

RE: Prusa Slicer First Layer Height Bug

The argument for this workflow is if you have applied mesh modifiers and custom settings changes to the object and then want to update the object to the latest .stl without having to reapply the modifiers and custom settings.

I have a similar thing, but my process doesn't seem to have this issue. I have a project file for printing a filament swatch with a couple small sample objects. The swatch is printed at 0.1mm layer height, but the sample objects are printed at 0.2mm layer height. When I want to print a new swatch I don't want to loose the object specific settings (layer height), so I load the new swatch stl as a part to the swatch object. Then I delete the part of the swatch object that was the previously printed swatch. I do have to move the object around since the imported part came in physically offset in both x and y, but for my application the auto place works well. All my swatches are the same z thickness, so I'm not sure if I would see a similar issue.

I didn't think of using the reload because each of my swatch stl files have a different filename because the brand and color are embossed text in the swatch.

RE: Prusa Slicer First Layer Height Bug

Posted by: RetireeJay

OK, following your workflow I was able to duplicate your results (to the point of seeing that the first layer becomes 0.8mm thick; I didn't try to print this). [...]

I'm very puzzled by this, as the printer firmware won't let you go below 0.15mm using normal G0/G1 moves for that 1st layer before triggering software end stops. I suppose if you ... for some reason ... had calibrated your Live-Z so badly that it was close enough to the bed, going to 0.15mm would indeed gouge the PEI surface, but at that point, I'd expect homing and mesh bed leveling to do the same. I think this is more of a hardware (mis)calibration issue than software.

That said, it would be reasonable for PrusaSlicer to dump any assumptions about a reloaded part and start from scratch. I wouldn't expect it to figure out what the hell you were trying to do beforehand.

For the love of god, get that Live-Z calibrated properly! A move to 0.08mm or anything else shouldn't cause damage.

RE: Prusa Slicer First Layer Height Bug

 0.08mm or anything else shouldn't cause damage.

We are not talking about 0.08mm, but 0.8mm, which is possible. This does not damage your print surface. My Live-Z adjust is spot on. 

I damaged my printsuface as a combination of the bug and a wrong decision on my side before I understood what happend. I was irritated because the the skirt printed fine, so I thought my Live-Z was fine. But after the model didn't want to stick I lowered Z Height to compensate, which lowered the nozzle to much for the next print.

RE: Prusa Slicer First Layer Height Bug

Standing by my "can't reproduce" satement.  I loaded the 25mm cube into Plicer.  I then copied the 24mm file over the 25mm file I had just loaded. Then I used "reload from disk" to grab the updated file, which should simulate an edit.   There was no change in first layer height.