Perimeter gap between Start and End  

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ruanlotter
(@ruanlotter)
Active Member

Heya!!

So I just got my first Prusa i3 Mk3s and really loving this printer - prints come out GREAT! Except for one small little issue. Very very small gaps on each layer where the walls start and stop. Now I think this is gCode related and NOT the printer, because I can see these gaps when I preview the print in PrusaSlicer. (see pictures below).

Now I sliced the same model in Cura (using my Ender 3) and it prints flawlessly. This is also not model related as it happens with everything I print.

PrusaSlicer:
https://imge.to/i/gsVgy
https://imge.to/i/gsJlt
https://imge.to/i/gsOtZ

Cura:
https://imge.to/i/gsbGG
https://imge.to/i/gso5x

Any ideas how to close these tiny gaps? Maybe a retraction issue? 🤔 

Thanks!
Ruan

Posted : 25/06/2019 10:32 am
joan.t
(@joantabb)
Veteran Member Moderator

Hi Ruan, 

are these gaps a problem in reality or a problem in the G code view...?

to my understanding of FDM 3D printing, there is always a stop and start position on every layer, except when using Spiral Vase mode...

Slic3r and Prusa control, tend to do each outline separately.   in  this Gcode Viewer ( https://www.gcodeanalyser.com/ ) there don't appear to be any gaps just adjacent start stops

view from G code Analyser

however the slic3r viewer makes more of an item of the stop starts... as below

Sliced in Slic3r PE and viewed in Slic3r PE   this viewer seems to show gaps at start stop positions

Kiss slicer crosses over between the outside perimeter and the inside perimeter to obscure layer stop start Sliced in KISS.  view from G code Analyser
starts and stops are inside the model and the extruder crosses over between inside and outside perimeter whilst travelling 
Your cura image seems to miraculously print without stopping and starting.

this could simply be a factor of the Cura imaging engine. have you tried looking at your Gcode in a different viewer?

sliced in cura and view from Cura4.1

above is what cura shows for the same STL there don't appear to be any stop starts

and below, is what a different gcode viewer shows for the same file

view from G code Analyser

in the other viewer you can see the cura layer stop start points...  about 12 o'clock position...

 

I also sliced in Simplify 3D

sliced in  S3D view from G code Analyser  which shows starts and stops at the 7 o'clock position
however if viewed in S3D, you get

which doesn't show starts and stops
All slicers handle these  points differently...

users select which  slicer suits them best, and use that.... (until they come across a problem, when they look elsewhere) lol.

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...
Posted : 25/06/2019 1:26 pm
ruanlotter
(@ruanlotter)
Active Member

Hi there! Thanks for the detailed reply.

It actually is visible in the real print, almost looks like tiny tiny holes. If you align the seems it appears as a line with tiny holes.
I have not tried printing the Cura Gcode, but I will test that tonight as soon as I get home.

Will reply here with my results.

If Cura works, then I will probably move over to Cura for my Prusa prints as well. Currently using PrusaSlicer for the Prusa and using Cura for my Ender 3.

Thanks again for the info.

Regards,
Ruan

Posted : 25/06/2019 2:41 pm
bobstro
(@bobstro)
Illustrious Member
Posted by: ruanlotter

[...] Any ideas how to close these tiny gaps? Maybe a retraction issue? 🤔 

Those gaps you're seeing in PrusaSlicer preview are the z-seam, where one layer stops and the next begins. They do leave a z-seam "scar" when printing. Unfortunately, that's just the way current consumer-grade FFF printing works. You can move the seam around under Print Settings->Layers and perimeters->Advanced->Seam position in PrusaSlicer, randomizing it (which tends to leave surface zits), or tucking it in corners if any exist (align or nearest). You can mitigate it by calibrating your extrusion multiplier under Filament Settings->Filament->Filament->Extrusion multiplier and by tuning Linear Advance. If you need a smooth surface, aligning it and sanding may be your best bet.

There's a more lengthy discussion here.

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 : 25/06/2019 3:51 pm
Neophyl
(@neophyl)
Noble Member

Actually it is possibly a slicer bug.  I opened an issue last week on github about something similar, https://github.com/prusa3d/PrusaSlicer/issues/2485 .  Yet to get an answer though.

In my case I have some single wall thickness parts that have several instances (some with the model added again and others duplicates) and a single part has gaps in the walls when printed, the duplicates do not.  When you examine the slice with show retract/unretract you can see that its not unretracting on the single problem part.  No idea why and if I slice it for a different printer it still has the gaps so I'm pretty sure its the slicer.

Posted : 25/06/2019 6:22 pm
vintagepc
(@vintagepc)
Noble Member
Posted by: Neophyl

Actually it is possibly a slicer bug.  I opened an issue last week on github about something similar, https://github.com/prusa3d/PrusaSlicer/issues/2485 .  Yet to get an answer though.

In my case I have some single wall thickness parts that have several instances (some with the model added again and others duplicates) and a single part has gaps in the walls when printed, the duplicates do not.  When you examine the slice with show retract/unretract you can see that its not unretracting on the single problem part.  No idea why and if I slice it for a different printer it still has the gaps so I'm pretty sure its the slicer.

Interesting, I've noticed this too and always thought oozing/idler tension was to blame. I just haven't had any prints where it's been a problem yet.

Posted : 25/06/2019 6:58 pm
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