Visibly thicker lines  

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Royk
 Royk
(@royk)
New Member

Hi,

 

I've decided to make a post simply because I'm getting fed-up with my Prusa MINI, support and Prusa altogether.

Let's start at the beginning of the year (literally 01-01-2021) when I contacted support for a problem which was bugging me for a while. While printing on my MINI I get thicker lines, seemingly randomly.

With the help of support and after testing, disassembling the printer, reassembling it and testing it a whole lot more, I got the OK to send the printer to Prusa HQ on 6th of March and shipped in on the 23rd to review the issue. Prior to sending the printer I was working on the hotend (it clogged up again, like so many times before) and I decided to install the Bondtech Heatbreak to resolve the clogging issue. I also installed an original E3D steel nozzle at the same time, for more printing options in the future and since the hotend was disassembled anyways (this was all done on the 4th of March).

 

After loads of mailing back-and-forth, asking for information and promises from the support tech (that were not kept) I received a few pictures with test prints that looked promising on the 18th of May (almost 1,5 months after sending the printer to Prusa HQ). The support tech had issues with my Bondtech Heatbreak and nozzle which required extensive testing (although I was told that sending the printer with these parts would cause no issues). He replaced these with the original parts from Prusa to test the printer and noticed the problems (thicker lines) stopped.

 

The printer was finally shipped on the 25th of May and I received it on the 28th. I've been running small prints ever since but decided to launch a 10 hour test of a castle today to verify that everything is ok (I had been noticing thicker lines in some prints, but those can happen, right). The printer is now in original condition, as received.

The print finished today at 5:30 PM as I arrived home from work. Upon inspecting the print I must say that I'm back to square one... So, hopefully some of you know what to about this, because my gut feeling says (and as you can imagine after half a year of testing and support from Prusa) that I'm done with the MINI and Prusa and I want my money back since it doesn't perform like expected.

 

Please review the pictures in my shared Google Photos folder:

https://photos.app.goo.gl/9a8Nuc4vVfy9rEZZ8

This topic was modified 2 days ago 2 times by Royk
Posted : 10/06/2021 6:57 pm
Royk
 Royk
(@royk)
New Member

I want to add to this that I'm using Prusa Slicer with all the default settings and profiles for the MINI.

Posted : 10/06/2021 7:06 pm
bobstro
(@bobstro)
Illustrious Member

I believe you are referring to those variations in what would be vertical surfaces as they print. Do you get the same variations when printing a perfectly vertical surface like a cube? There is a common phenomenon that you'll encounter as vertical surfaces vary ever so slightly during a print. This is the infamous "buldge" that occurs as layers transition:

  • Between solid infill and sparse infill.
  • Between sparse infill and gap fill
  • When the number of perimeters increases or decreases between layers.
Happily, this was described as a "buldge" in an early post and that misspelling has made the problem very easy to search for. It's not truly a bulge but can give that appearance in some circumstances. There are several 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:
  • Be sure you're not just seeing the effect of minor warping/lifting/curling along edges or in corners. This can really throw troubleshooting off. Rotate the print and verify the problem occurs in the same place.
  • 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.
Unfortunately, with the current state of FFF consumer-grade 3D printing, we still have to do some hand-tuning for specific prints. I've gotten to the point that I can usually eliminate the effect to my satisfaction. Dig through those threads for examples. Contrary to some theories, this is not exclusively a PrusaSlicer thing.
 
In your specific example, slice the part and spend some time in preview mode checking to see if the defect aligns with any shifts in infill, solid layers, transition from perimeters to sparse infill or gap fill, etc. If you'd save your part & settings off in a 3MF project file, zip it up, and attach it to a reply here, we may have better suggestions.
 
The Prusa Benchy hull line notes might also be interesting.
 
Looking at your pictures, it appears (to me) that you might be able to tune this issue out a bit, but pictures under specific lighting conditions -- particularly from above -- will highlight surface inconsistencies. Sanding may be required if you need a truly consistent surface. 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.
This post was modified 2 days ago by bobstro
My notes and disclaimers on 3D printing 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...
Posted : 10/06/2021 10:50 pm
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