Thin gap between outer wall and inner wall, only on small circular insets but not on the perimeter of the print...

[roykinn7 0]

Firstly, I love Cura, been using it for a year, it keeps getting better and better! Thanks

I've been going crazy over this issue for months now, I've posted asking for help on r/3dprinting and the wanhao duplicator i3 google group and nothing I've tried works, or at least what does work messes something else up.

I've built some game hex pieces that have circular insets built around the perimeter to allow for tiny magnets. Every other detail of the print comes out great but these particular insets keep printing with this gap between the inner and outer walls.

What baffles me is if I print the same size inset into a small piece of plastic like a tiny game piece they come out perfectly fine. These gaps appear all the way around the outer wall on each inset, sometimes slightly touching the inner walls but mostly there is a visible gap. Here is a blender mockup I built to visualize the problem better.

The STL looks fine in Cura, here are screenshots of the STL and viewed in Layer Mode.

I've tried many many things...

...adding an infill and skin overlap of .2 then .4mm

...playing with my retraction settings (I thought maybe as the printer retracted to travel from one inset to the next it was under extruding when it got to there.)

...I tried to give Compensate Wall overlap a negative value to increase overlap between inner and outer wall but the software is currently just a check box.

...I've got Fill Gaps Between Walls set to Everywhere.

...I slowed my Outer Wall print speed down to 10mm/s

The only thing that fixed the matter ruined every other bit of my print, by editing the Outer Wall Inset by about .2mm the outer wall overlapped the inner wall and printed with no gap. But not only does this throw off all of my tolerances which I had to recalculate it also makes for poorly printed small details, so I had to abandon that "fix".

The models are built in Fusion 360.

I'm printing on a Monoprice Maker Select V2.1

That's a .4mm nozzle.

I've tried multiple different brands of PLA, printing from 195-205f.

The insets have a diameter of 3.325mm, I'm wondering if this is causing a problem with the nozzle width, but even that doesn't make sense to me, again, these holes print out just fine one at a time.

Anybody out there that can shine some light on why I'm having so much trouble here? I think my hair is graying over this nonsense :/

[JasonC 1]

Did you manage to fix this issue? I'm getting the same problem.

[roykinn7 0]

57 minutes ago, JasonC said:

Did you manage to fix this issue? I'm getting the same problem.

It's been awhile since I used cura, upgraded to a prusa and have been using slic3r since so my recollection isn't perfect but here are two things that helped but did not completely rid me of the problem...

 

1. At first I had some success using what I think was called the inner wall offset setting and pushing the inner wall closer to the outer wall, or maybe it was outer wall offset pushing closer to the inner wall. I think I remember the problem with this is it changed the dimension of the hole, so it was likely the latter of the two. You can also play with the order in which it prints the walls too, outer before inner or vice versa.

 

2. What worked better was a new setting that came along, last time I used it the setting was in experimental. It was called something like wall print optimization, it would calculate the wall printing order so that, if say, the model had two holes or more on a surface like the print above it would print hole #1, outer to inner walls or inner to outer before moving to hole #2.

 

This worked best, I think the problem had something to do with printing all outer walls first and the time it took before it came back to each hole to print the inner walls would allow for the tiny outer walls to cool and contract, shrinking and creating the gap

 

Since the wall order optimization setting forces the printer to print each hole individually before moving to the next the outer and inner wall have the time to properly fuse together before the first wall retracts. That's just my guess, but iirc it seemed to help if not in some instances completely fix the issue.

 

Make sense? I'm not totally sure it does.

[JasonC 1]

Thanks for reply.

 

Yes that makes perfect sense. I've been experimenting with the optimise wall function but for other reasons so maybe that is what is helping on some models but not others. I will look into that further and see what I can find.

 

I also run a 2 Prusas but never tried slic3r so maybe I'll take a look at that if I can't improve things.

 

Thanks again for you help.

[AbeFM 32]

On 8/24/2017 at 7:14 PM, roykinn7 said:

 

I've tried many many things...

...I tried to give Compensate Wall overlap a negative value to increase overlap between inner and outer wall but the software is currently just a check box.

The only thing that fixed the matter ruined every other bit of my print, by editing the Outer Wall Inset by about .2mm the outer wall overlapped the inner wall and printed with no gap.

Did you find that shutting off Compensate Wall overlap altogether helped? I'm experimenting with shutting that off and also turning off combing (which may actually be fixed but not released yet).

 

 

On 3/3/2018 at 5:11 AM, JasonC said:

I've been experimenting with the optimise wall function but for other reasons so maybe that is what is helping on some models but not others. I will look into that further and see what I can find.

 

I also run a 2 Prusas but never tried slic3r so maybe I'll take a look at that if I can't improve things.

 

It's been years since I used Silc3R, but several objects just wouldn't come out usable, so generally after a day on the forums, I just bring prints I want to look good into slic3r. It breaks up my workflow to have to switch all the time, but it works.

[roykinn7 0]

4 hours ago, AbeFM said:

Did you find that shutting off Compensate Wall overlap altogether helped? I'm experimenting with shutting that off and also turning off combing (which may actually be fixed but not released yet).

Compensate Wall overlap never did anything for me, it wouldn't allow me to add a negative value to extend the overlap.

4 hours ago, AbeFM said:

 

It's been years since I used Silc3R, but several objects just wouldn't come out usable, so generally after a day on the forums, I just bring prints I want to look good into slic3r. It breaks up my workflow to have to switch all the time, but it works.

I use slic3r often now that I'm running a Prusa i3 MK2S, but like I said above, the smaller details like this print easier on the Maker Select using Cura's Optimize Wall Printing Order setting, this lets the printer concentrate on once section of the print at a time which I believe keeps the inner walls from shrinking while the print is working on other parts and before it travels back to extrude the outer walls. This, I think, was my problem. But I also kinda sorta gave up on tweaking it as I've found that, for what I'm aiming at with these specific prints (selling on etsy), an FDM machine just won't cut it... looking at purchasing an SLA printer sometime down the line.

[peterlecoz 0]

Inner wall printing speed is by default twice the outer wall printing speed. 

For some reason (defective noozle, defective extruder system, installation of a stepper damper on the extruder ... ) higher speed could lead to underextrusion. Therefore, inner wall gets printed too thin. That make gaps between walls. 

If you reduce inner wall speed (make it equal to outer wall speed), you might temporarily fix these gaps.

But the best way to solve this, is to find out why extrusion is too low at higher speed. 
  




 

[randyinla 12]

I used to have this issue when I first started using my U2 a few years ago. My settings evolved over the years and I eventually have come to the point of setting my Line Width to 0.015mm narrower than the nozzle, so .385mm for a .4mm nozzle or .235 for a .25mm nozzle, Wall Thickness between multiples of that (.77 for 2 walls, 1.155 for three etc.) and multiples of the nozzle width (.4, .8 or 1.2 etc.), and I make sure to print hot enough so the walls melt into one another better.  I also turn on the Outer before inner walls shell parameter.  Since you are only experiencing this on small holes, maybe try playing with the Horizontal Expansion parameter?  That allows you to increase/decrease hole sizes while also decreasing/increasing outer dimensions.  I imagine increaing the holes this way will have zero effect on the distance between the walls, but it's worth a try.  I haven't been able to force a fingernail in between walls for a few years now.  Good luck!

Edited June 5, 2019 by randyinla

[henderpa 0]

(Forgive the cross-posting, but this topic appears in several places in the forum and I've yet to find a solution.)

______

I have this problem as well, all the time, with Cura. I don’t experience it when testing other slicers. I don’t know what’s causing it, but I know what it isn’t (and I’ve searched and combed through various forum threads with no solution). Here's what I've eliminated so far:

 

—"Optimize Wall Printing Order" does not fix this problem for me, whether it’s checked on or off makes no discernible difference to this.

 

—It happens with curved lines/circles, but doesn’t happen with straight lines. So, amping up the flow rate/extrusion on walls does not fix the problem, because to see any difference I would have to turn it by 25% and by then all other walls (straight lines) become massively overextruded.

 

—It’s not a speed issue. I have tried printing at 20mm/s, 40, 60, 100—it happens at all speeds (it’s slightly worse at very high speeds, but it’s bad always).

 

—It’s not a gcode flavour mismatch; I’m running Marlin and have set Cura to Marlin firmware (as I have any other applicable slicers I’ve been using to test). Note: this was also happening on stock firmware, which is why I switched to Marlin in the first place.

 

—It’s not my hardware, given that the problem is limited to Cura slicer.

 

—It’s not layer height; I have tried 0.1mm to 0.4, and the only difference is how many layers have gaps, not the size of the gaps.

 

—It’s not nozzle width. I’m careful to set my nozzle width properly and have tried 0.2mm to 0.6mm nozzles. It persists on all of them (only the size of gap changes).

 

—It’s not wall width. I can set that to 5mm, it still will form a gap around the 5mm curved line.

 

—It’s not temperature; it happens across the range. Also, I’ve tried different cooling amounts (fan speeds).

 

—It’s not the filament; it happens with PLA, PETG, and ABS, and across manufacturers.

 

—If the solution is retraction/combing/coasting settings (big "if), then it’s some very precise combo of those three. I’ve tried a range of retraction/comb/coast settings on the above filaments and the issue persists across those ranges.

 

—I’ve tried "ironing" the top surface but this is a bandaid solution—the gaps exist throughout the print, just not in that one top ironed layer. So it can produce an okay surface, but it doesn’t fix the underlying structural problem.

 

—It’s not ambient moisture. Filaments are printed direct from a drier or from the spool holder if recently dried.

 

—It’s not the enclosure around the printer; it was happening before I put an enclosure around it (which I thought would help solve the issue).

 

—It’s not bed adhesion or leveling. This has happened across multiple levelings and in any case, it happens even at the top of tall prints where the circular hole is only in the top few layers.
______
 

Any other likely candidates for what might be causing this? Such a shame that an otherwise great piece of software would have trouble with such a basic thing.

Addendum: Horizontal Expansion does not fix it for me, and my Inner wall speed is always matched to my Outer wall speed.

[burtoogle 493]

Hello @henderpa, could you please provide a sample project file that exhibits the issue? Do File->Save and attach the .3mf file to this thread. Thanks.

[henderpa 0]

3 hours ago, burtoogle said:

Hello @henderpa, could you please provide a sample project file that exhibits the issue? Do File->Save and attach the .3mf file to this thread. Thanks.

Thanks, @burtoogle. Here's a sample file, but it's not exclusive to this one by any means.

GapHoleSample.3mf

[burtoogle 493]

What size nozzle are you using?

[burtoogle 493]

Anyway, it looks to me that you are trying to push a lot of plastic, can your extruder/hotend really deliver 16.8mm^3/S ?

The printing temp is hot for PLA so I would have thought that you would see quite a bit of shrinkage as it cools? Maybe it would be worth trying a lower print temperature and reduce the print speed and/or layer height to cut down the required extrusion rate.

[henderpa 0]

Hi burtoogle, thanks for your thoughts. I currently have a 0.5mm nozzle on it, and when equipped that way my lines range from 0.4 to 0.6mm in width, and heights from 0.1-0.4mm depending on what I want to achieve with the model. I sometimes print with a nozzle as small as 0.2mm and the issue remains (albeit with smaller gaps). Haven’t seen any other underextrusion issues apart from around the circles, and as I mention above the same model and machine via a different slicer doesn’t end up having the gaps (with same speed and temp, which I hadn’t pointed it out but when I was testing Prusaslicer, for example, it was set as close to my Cura settings as I could get). Also, it doesn’t matter how slow I go or where I set the temp—if the rest of the model is bang on, the circular holes are still an issue. (Oh, re: temps, the filament I was using on that one was a PLA that likes it a bit hotter. The temperature was arrived at after several bridging and retraction tests.)

 

Anyhow, I’ll see if I can lower the temp to as low as it will go and still allow adhesion, and I’ll drop the volumetric output accordingly, to see if those are the issue.  I suspect it’s some combo of the sequence in which Cura is programmed to prioritize the holes vs the rest of the structure; the way it handles travels (have tried a range of travel speeds between 90 and 150mm/s); and the amount to which the holes cool before their adjacent walls are laid down. I -do- notice that in a given layer, it will print each hole in its entirely (all walls) first before connecting them, so I gather they’re shrinking before the walls get built around them.

Edited August 1 by henderpa
A parenthetical was accidentally deleted

[Tomahawk_101 1]

Henderpa,

I saw you mentioned horizontal expansion. Have you tried using the hole expansion setting to improve your results?

There's more info on those settings here: https://support.ultimaker.com/hc/en-us/articles/360012512340-Shell-settings

Edited August 1 by Tomahawk_101

[henderpa 0]

Hi Tomahawk_101, I haven’t! I hadn’t realized there was a hole-specific expansion setting! I’ll try that out today and report back, thank you!

[henderpa 0]

Update: no luck with hole expansion—it appears to do the same thing as horizontal expansion, but applied only to holes. That is, it makes the hole itself larger or smaller, but does nothing to fix the gaps where the walls meet the rest of each layer.