Spiky edge on low slope surface caused by retraction
 
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PrusaTester2020
(@prusatester2020)
Estimable Member
Spiky edge on low slope surface caused by retraction

Hi!

I need to print a 3D model with a low slope edge using PrusaSliser. The problem is that if I print it using PLA and 0.4mm nozzle at 0.20mm layers the retraction causes very unpleasant spikes on the edge as seen on the pictures:

Here is the part of the 3D model that causes problems:  https://www.udoma.org/tmp/PrusaMini/SharpEdge.3mf

I have no option to change the orientation because it's a complicated model.

My obzervations are:
- Changes to retraction (Length) from 0.2 to 3.2 to 6.0 did not cause any improvement.
- Changes to retraction (Lift Z) from 0.2 to 0.4 did not cause any improvement.
- Changes to temperature from 200C to 220C did not causes any improvement.
- Changes to layer from 0.20mm to 0.10mm causes improvement BUT the print time jumps significantly.

Any idea how to move these retraction points to different part of the model OR other way to get rid of them WITHOUT changing the orientation, speed and layer thickness?

Posted : 17/02/2021 6:34 am
Neophyl
(@neophyl)
Illustrious Member
RE: Spiky edge on low slope surface caused by retraction

have you tried turning retraction off completely, ie set it to 0 ?

Posted : 17/02/2021 6:57 am
Diem
 Diem
(@diem)
Illustrious Member
RE: Spiky edge on low slope surface caused by retraction

The simplest is to use  small sanding block and fine grit wet and dry paper to give it a very light sanding - just enough to take off the points without affecting the rest of the surface.  It should take about ten seconds.  Think lf it as a quick, final, polish.

Cheerio,

Posted : 17/02/2021 2:18 pm
bobstro
(@bobstro)
Illustrious Member
RE: Spiky edge on low slope surface caused by retraction
Posted by: @prusatester2020

[...] Any idea how to move these retraction points to different part of the model OR other way to get rid of them WITHOUT changing the orientation, speed and layer thickness?

I'm assuming you're on a Mini based on the pic. The two things I've found to make the biggest difference with these sorts of issues are: 

  • Ensure the filament is dry. PLA doesn't absorb moisture as readily as nylon, but it can still happen. Dry the spool to make sure you're not fighting basic filament issues.
  • Calibrate your extrusion multiplier for each filament. If you are using Prusa filament profiles, this is less of an issue, but other brands often over or under extrude very slightly when using default extrusion multipliers. If your slicer settings don't accurately reflect your physical printer and filament parameters, a bit of over extrusion can aggravate these sorts of problems.

 

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 : 17/02/2021 6:45 pm
PrusaTester2020
(@prusatester2020)
Estimable Member
Topic starter answered:
RE: Spiky edge on low slope surface caused by retraction

Guys thank you for suggestions 🙂

1. @neophyl:  Turned retraction off completely and to my surprise I received a perfect result after 6 hours 3D print without any stringing/oozing - amazing!

2. @diem: I tried a very light sanding and also not so light sanding on one of my older 3D prints and after 20 minutes the result was satisfying but not perfect.

3. @bobstro:
A. I always make sure the PLA humidity is no more then 20% all the time - usually 15%. Is this OK? 
B. I did not recalibrate the extruder multiplier for this filament but will try setting filament multiplier to 0.9, 0.8 and 0.7 which should have similar effect - am I correct?

This post was modified 3 years ago 2 times by PrusaTester2020
Posted : 17/02/2021 9:31 pm
mrstoned
(@mrstoned)
Reputable Member
RE: Spiky edge on low slope surface caused by retraction

I use a small blowtorch a quick pass over and then i just run my thumb over it **CAREFULLY** as pla-tips are sharp.

https://www.biltema.se/fritid/friluftsliv-och-camping/gasolkok/minisvets-2000040527

Prusa Mini+ kit (4.3.4). BondTech extruder.
Prusa MK3S+ kit.

Posted : 17/02/2021 10:09 pm
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