Can anyone explain why Bridges generated by PrusaSlicer are SUPER THICK?? (and super slow due to my VFR limitations)
Trying to understand the reason for some strange problem.
All of my prints (different print profiles) generate strange settings for the Bridging. It appears that all the bridges are enormously thick, and due to limitations of VFR (~12mm3s) are printed at extremely slow speed and don't act as bridges at all.
Checked my settings 5 times and don't find any reason. Any guess?
P.S. "Thick bridges" is OFF. (and actually does not affect the result)
Best Answer by Neophyl:
That thick bridges is a legacy setting that slices all bridges with the same thickness as the nozzle width as you noticed. So regardless of your layer height it assumes the bridging layer will be the nozzle diameter, precisely for the reasons Joan enumerated.
However that slicing assumption while logical on the surface didn't always hold up which is why many of use raised and supported a software change request for them to make it possible to turn off that assumption and slice it with an assumed layer height the same as what is configured. In many cases turning that option off results in better bridging.
While we managed to persuade them to give us a setting for this, they decided NOT to apply that logic to bridge infill for some bizzaro reason. As such it doesn't effect that and there is zero you can do about it in PS. It will apply for an actual bridge where its printed in air though.
It's one of the reasons I was using Super Slicer previously and am anxiously awaiting a new version that will have the PS 2.6 and 2.7 features rolled into. Until that time I sort of swap between PS and SuSi.
RE: Can anyone explain why Bridges generated by PrusaSlicer are SUPER THICK?? (and super slow due to my VFR limitations)
UPDATE: made slicing for 0.05 layer height, all speeds 65mm/s to ensure all the print lines will be at the maximum speed. We can see that Bridges are still slow due to enormous thickness, and limited VFR
Looks like at all layer height slicer generate the SAME thickness of the bridges. In the case of low layer height - we can see the very different speed. In case I will set 0.4 layer height, everything will be printed at roughy the same speed (so the VFR/Thickness of Perimeters will roughly be the same as Bridges)
Tests @ 0.05 layer height:
RE: Can anyone explain why Bridges generated by PrusaSlicer are SUPER THICK?? (and super slow due to my VFR limitations)
total guess,
layers are constrained by space between nozzle and layer below, bridges are not constrained from below so the extruded filament will not be squished to a thin film. and will appear thicker than desired and poorly bonded to adjacent strands.
regards Joan
I try to make safe suggestions,You should understand the context and ensure you are happy that they are safe before attempting to apply my suggestions, what you do, is YOUR responsibility. Location Halifax UK
RE: Can anyone explain why Bridges generated by PrusaSlicer are SUPER THICK?? (and super slow due to my VFR limitations)
That thick bridges is a legacy setting that slices all bridges with the same thickness as the nozzle width as you noticed. So regardless of your layer height it assumes the bridging layer will be the nozzle diameter, precisely for the reasons Joan enumerated.
However that slicing assumption while logical on the surface didn't always hold up which is why many of use raised and supported a software change request for them to make it possible to turn off that assumption and slice it with an assumed layer height the same as what is configured. In many cases turning that option off results in better bridging.
While we managed to persuade them to give us a setting for this, they decided NOT to apply that logic to bridge infill for some bizzaro reason. As such it doesn't effect that and there is zero you can do about it in PS. It will apply for an actual bridge where its printed in air though.
It's one of the reasons I was using Super Slicer previously and am anxiously awaiting a new version that will have the PS 2.6 and 2.7 features rolled into. Until that time I sort of swap between PS and SuSi.
RE: Can anyone explain why Bridges generated by PrusaSlicer are SUPER THICK?? (and super slow due to my VFR limitations)
Thanks Joan! I've got the same response on our local forum, and you're fully right, but this is not what is wrong 🙂 Yes, the "geometry of the line that is only supported by the air is expected to be not ideal 🙂
Wrong is that PrusaSlicer due to some reason tries to squeeze 5-8 times more plastic in case of Bridges.. And I can't find any Settings or explanations to this. It acts like if Flow Ratio for Bridges is 5-7. But it is 1. (actually I temporarily set it to 0.35 and that somehow hacked by problem)
total guess,
layers are constrained by space between nozzle and layer below, bridges are not constrained from below so the extruded filament will not be squished to a thin film. and will appear thicker than desired and poorly bonded to adjacent strands.regards Joan
RE: Can anyone explain why Bridges generated by PrusaSlicer are SUPER THICK?? (and super slow due to my VFR limitations)
Spot on! I started to have exactly the same feeling, and you 100% confirmed it!! Thanks mate!
I just made Bridges Flow to 0.35, but will have to fine-tune this for every Nozzle/Layer/Etc settings
P.S. Re-read Joan answer and now I can at least understand what was the reason for such a strange algorythm..
That thick bridges is a legacy setting that slices all bridges with the same thickness as the nozzle width as you noticed. So regardless of your layer height it assumes the bridging layer will be the nozzle diameter, precisely for the reasons Joan enumerated.
However that slicing assumption while logical on the surface didn't always hold up which is why many of use raised and supported a software change request for them to make it possible to turn off that assumption and slice it with an assumed layer height the same as what is configured. In many cases turning that option off results in better bridging.
While we managed to persuade them to give us a setting for this, they decided NOT to apply that logic to bridge infill for some bizzaro reason. As such it doesn't effect that and there is zero you can do about it in PS. It will apply for an actual bridge where its printed in air though.
It's one of the reasons I was using Super Slicer previously and am anxiously awaiting a new version that will have the PS 2.6 and 2.7 features rolled into. Until that time I sort of swap between PS and SuSi.
RE: Can anyone explain why Bridges generated by PrusaSlicer are SUPER THICK?? (and super slow due to my VFR limitations)
I notice if you turn on verbose gcode output that the bridge infill lines look like thios
G1 X108.735 Y107.585 E.08606 ; infill (bridge)
G1 X108.735 Y108.225 E.03387 ; infill (bridge)
G1 X108.023 Y108.938 E.05332 ; infill (bridge)
With the relative extrusion values I'm wondering if the regex gcode replacement function or a post processing script could isolate those lines and say divide the E value by 3 or similar. That would get you the thinner extrusion on Bridge infill without having to mess with the basic bridging ratio.