Looking to Solve Unwanted, Wide Perimeter Overhang Starts after Bridging
Hi All,
I encounter an unwanted perimeter overhang when my print reaches a bridge. Or at least that's my rookie observation. Since I can't explain well, I included photos to do the talking.
Depending on my Fusion model tweaks, I may experience less of overhang, but it's always present. And since the model looks fine in Slicer, I deduce it's the print and not the model
PRINTER: Mini+, but have encountered the same issue with I3 MK3S.
FILAMENT: Prusament PETG ...but experiencing this with all PETG brands.
SOFTWARE: Prusa Slicer 2.3.0
Best Answer by bobstro:
I *think* what you are seeing is the infamous "buldge" that occurs as layers transition:
- From solid infill to sparse
- From sparse infill to gap fill
Happily, this was described as a "buldge" in an early post and that misspelling has made the problem very easy to search for. There are 2 threads you might want to look through:
Unfortunately, no single fix has been identified that will work in all cases, but a few things that help:
- Slow down external perimeter speeds (and all speeds in general). If the nozzle is moving a bit too fast, you get slight under extrusion on some layers. These are apparent as adjacent layers print with slightly different extrusion rates. I use 25mm/s for external perimeters when appearance is important.
- Calibrate your extrusion multiplier for each filament. Any slight over or under extrusion can produce very small but noticeable variations in layers with different features (e.g. infill, gap fill, top solid infill). The closer your slicer settings match your actual printer and filament, the more accurate the gcode will be.
- Calibrate linear advance (LA) for each filament. LA adjusts the flow of filament to compensate for acceleration and deceleration. If it's not right, you may see artifacts even away from features such as bumps or hole on the same layer. In some cases, a hole on one wall causes imperfections on the far side of the print.
- Add an external perimeter if vertical walls allow it. The thicker combined perimeter allows the filament flow to even out.
- Tweak perimeter extrusion widths. The problem can appear when the slicer switches between gap fill, sparse infill, and solid or top infill. If you can find a multiple of perimeter widths that minimizes these transitions, it can work for a specific print.
- If you are the part designer, make vertical free-standing walls thicker. IME, at 1.5mm thick, the problem is less noticeable. You can try for a multiple of extrusion widths, although be aware the PrusaSlicer does some internal calculations for overlap between extrusions that can throw you off.
I've gotten to the point that I can usually eliminate the effect to my satisfaction. Dig through those threads for examples. You might want to follow the Cura slicer development. They've recently released an Alpha of their Arachne slicing engine that dynamically adjusts perimeters based on wall thickness. It's still early alpha, and not yet producing ideal results, but it's worth a look. There's a lot of cross-fertilization between slicers, so something similar may evolve for PrusaSlicer in the future.
RE: Looking to Solve Unwanted, Wide Perimeter Overhang Starts after Bridging
I should mention:
Using Prusament PETG default Setting at 0.2 Quality
Changed Printer Settings: Perimeters to 3 and Infill to 20% Grid
That's it 🙂
Apparently this is a "thing."
Here's a link:
https://help.prusa3d.com/en/article/the-benchy-hull-line_124745
RE: Looking to Solve Unwanted, Wide Perimeter Overhang Starts after Bridging
I *think* what you are seeing is the infamous "buldge" that occurs as layers transition:
- From solid infill to sparse
- From sparse infill to gap fill
Happily, this was described as a "buldge" in an early post and that misspelling has made the problem very easy to search for. There are 2 threads you might want to look through:
Unfortunately, no single fix has been identified that will work in all cases, but a few things that help:
- Slow down external perimeter speeds (and all speeds in general). If the nozzle is moving a bit too fast, you get slight under extrusion on some layers. These are apparent as adjacent layers print with slightly different extrusion rates. I use 25mm/s for external perimeters when appearance is important.
- Calibrate your extrusion multiplier for each filament. Any slight over or under extrusion can produce very small but noticeable variations in layers with different features (e.g. infill, gap fill, top solid infill). The closer your slicer settings match your actual printer and filament, the more accurate the gcode will be.
- Calibrate linear advance (LA) for each filament. LA adjusts the flow of filament to compensate for acceleration and deceleration. If it's not right, you may see artifacts even away from features such as bumps or hole on the same layer. In some cases, a hole on one wall causes imperfections on the far side of the print.
- Add an external perimeter if vertical walls allow it. The thicker combined perimeter allows the filament flow to even out.
- Tweak perimeter extrusion widths. The problem can appear when the slicer switches between gap fill, sparse infill, and solid or top infill. If you can find a multiple of perimeter widths that minimizes these transitions, it can work for a specific print.
- If you are the part designer, make vertical free-standing walls thicker. IME, at 1.5mm thick, the problem is less noticeable. You can try for a multiple of extrusion widths, although be aware the PrusaSlicer does some internal calculations for overlap between extrusions that can throw you off.
I've gotten to the point that I can usually eliminate the effect to my satisfaction. Dig through those threads for examples. You might want to follow the Cura slicer development. They've recently released an Alpha of their Arachne slicing engine that dynamically adjusts perimeters based on wall thickness. It's still early alpha, and not yet producing ideal results, but it's worth a look. There's a lot of cross-fertilization between slicers, so something similar may evolve for PrusaSlicer in the future.
and miscellaneous other tech projects
He is intelligent, but not experienced. His pattern indicates two dimensional thinking. -- Spock in Star Trek: The Wrath of Khan
RE: Looking to Solve Unwanted, Wide Perimeter Overhang Starts after Bridging
@bobstro
Thank you. I’ll get to it!
RE: Looking to Solve Unwanted, Wide Perimeter Overhang Starts after Bridging
I would say the thin area of your part is curling in a bit as it gets taller, and would suggest trying it with some type of support that maintains its distance from the body of the print, and see if it still happens.
also you could probably just measure and see if the distance has been maintained.
The Filament Whisperer
RE: Looking to Solve Unwanted, Wide Perimeter Overhang Starts after Bridging
@swiss_cheese
Thought the same at first, but too many deliberate bulges.
The links provided in the fist few replies tell the tale....and here’s another link:
https://github.com/supermerill/SuperSlicer/issues/796
thank you
RE: Looking to Solve Unwanted, Wide Perimeter Overhang Starts after Bridging
For anyone who is following, I've come across the infamous Benchy hull line - Perimeter bulging. While I have trouble explaining this issue myself, please look at the blue model within this string - VERY telling. Notice the perimeter shifts when Prusa Slicer detects a new pattern (holes, layers, angles).
Also, @bobstro provides links within this thread that are very helpful and a deep dive into the issue. I will consolidate links for you below 🙂
For my particular model, I couldn't find any option or combination of options within Prusa Slicer 2.3.0 that would solve or improve my situation. HOWEVER, I came across a link to Prusa Super Slicer (Beta 2.2). I didn't have to go beyond Super Slicer's default settings to achieve a PERFECT PRINT the first time. I can't guarantee this will work for all, but it did for me....and some others.
I LOVE Prusa Slicer, but I struggled through 17 print revisions (5 hours each) before I opened Super Slicer. Don't worry, it's identical to Prusa Slicer.....with more options.
NOTE: Perhaps, if you don't have the same luck as me, at least you will have more options to improve the problem.
-------------------------------------
Here's the link to Super Slicer 2.2. Just a note for beginners...your computer may not trust the file. It's ok...allow it : )
https://github.com/supermerill/SuperSlicer/releases/tag/2.2.53.4
-------------------------------------
These links are from @bobstro
Thanks,
Kent
RE: Looking to Solve Unwanted, Wide Perimeter Overhang Starts after Bridging
FINAL LOG : )
I gave Super Slicer such a rave review, but....
Whereas Super Slicer helped remedy my bulging perimeter, I noticed a few random artifacts on my print. Of course I need to dig deeper into Super Slicer options, but the default settings can generate some random results.
1. A random seam was generated in a location I wasn't expecting. I adjusted the seam option, but the seam remained. It was not a clean seam. I had to use and knife to cut away some of the mess.
2. My print created random worm-type objects extruding outward from the perimeter. They were very easy to remove afterward, but strange.
All-in-all, I can see some great things in Super-Slicer, but can see, literally, why it's in beta : )
Thanks
Kent
RE: Looking to Solve Unwanted, Wide Perimeter Overhang Starts after Bridging
Welp... switching to PETG to PLA...the bulging is back...even with Super Slicer. Throughout Forum Land, I can see this issue has not been solved, other than folks switching to Cura.
RE: Looking to Solve Unwanted, Wide Perimeter Overhang Starts after Bridging
Ok, I'm being beyond ridiculous, but....using Super Slicer and all its added options, I was able to dial in and get a perfect print for PLA. Ok, I'm gone forever......
RE: Looking to Solve Unwanted, Wide Perimeter Overhang Starts after Bridging
So how did you get rid of the bulge? Could you export your profile? Thanks