Looseness around holes

[henderpa 0]

That’s... disconcerting. Haha.

[Adam324 13]

When I have had this problem, heat or nozzle clogs have been the culprit often.

 

-  I  had the heat too high and filament was leaking out of the nozzle before it moved to the parts where there were larger travels to other parts.

- The heat was too low and the extruder had problems pushing filament out but that was also noticeable in other areas.

- Nozzle partly clogged... also noticeable in other areas.

 

If it is heat related for that one printer, Maybe the thermistor is not working properly and showing the temperature a lot higher or lower than what the actual temperature is.  My thermistor has changed over 2 to 3 years and now the temperatures are about 10 to 15c lower than what it shows (Duplicator 9 printer).  I have used a fluke meter with a temp sensor to check it over the years.   (After realizing this awhile back, I have just adjusted my temperatures up 10 - 15c to compensate and finally recently ordered a new thermistor).  Maybe your temps on that one printer are way off from the other printers.

 

At the end of the print, after the nozzle has cooled on all 3 printers, Is there a big difference with how much filament is hanging out of the nozzle with the printer that is having the problems?  You need to use the same material of course on all 3 for the test with the same filament.  I usually get about 10mm or so with my printer after it cools.  That is specific to my printer, filament, and temps of course and can't be used for comparison to anyone else's printer.  You are just trying to compare between your 3 printers though and use your other 2 printers as a reference.

 

If the temp reading is off and reading too high for the actual temperature, you will likely get a lot more oozing out of that 1 printer after the print.  If that is confirmed, try reducing temps on that one printer by 5 degrees at a time and see if it helps.  If it isn't oozing at all, then maybe try increasing the print temp by  5 degrees at a time.

 

Edited August 2, 2020 by Adam324

[Arak0n 0]

I unfortunately see this exact same issue. It may be related to how using a concentric pattern on top and bottom will also leave very specific gaps, causing a flat print to have "hinges" cause there's a gap through the entire print.

90% of the circles I print on 2 very different printers (Mendel90 and Ender 3) exhibit this issue, no matter the settings, originally in Cura 4.1.0, still happening in Cura 4.6.2 now.

Note the peg on the left.. it drew 3 very distinct, seperate lines that are much smaller than wall line width. Right hole, also gaps. 

 

 

[henderpa 0]

@Arak0n, this is the best example of this that I’ve seen so far, and shows why it’s so frustrating—that peg is going to be very weak indeed, because the slicer turned it into pastry. It also demonstrates to me that it’s not an issue of cooling time between parts of a layer; my theory at one point had been that it’s due to Cura telling the printer to print interior of those hole-walls first, which then cooled (and contracted) while the printer did the rest of the layer before returning and doing the others, which no longer contacted the now-contracted lines.

 

But since on your model there’s only the peg part for those higher layers, there’s nowhere for the nozzle to go to let the lines cool and yet it’s -still- happening.

 

This furthermore tells us that it’s nothing to do with infill. Because if too little infill were pulling the walls away from each other on the holes, the peg wouldn’t be a problem.
 

I am increasingly convinced this is a bug within Cura; that there’s some calculation it applies when determining line width or extruder flow for rounded edges that causes it to underextrude only curved lines, and only at certain scales.

 

(Since you posted your printers: I was seeing this on an Anycubic Mega S, both with stock and Marlin firmware. It happens even if I print with default settings [0.2mm Normal] from Cura.)

[Arak0n 0]

Got an even better picture. First layer. You might say it's bed leveling, but I'm using a BLTouch and the issue wanders if I rotate the model. Adhesion is bad cause the lines are so thin and have barely the surface to attach.

On top of that, it also happens if I print on support, so it's not "lack of squish". Mind you, I can close the gap by making the nozzle drag on the bed, but that's kind of not the idea.

It's literally drawing two very thin walls around the hole and completely skipping the third wall., even though it's showing in the slicer.

But not on all holes, and you can see that other lines around it were drawn together properly.

Edited August 19, 2020 by Arak0n

[burtoogle 513]

Hello @Arak0n, could you please provide the project file for that print? Do File->Save and attach the .3mf file to this thread. Thanks.

[burtoogle 513]

15 hours ago, henderpa said:

I am increasingly convinced this is a bug within Cura; that there’s some calculation it applies when determining line width or extruder flow for rounded edges that causes it to underextrude only curved lines, and only at certain scales.

 

I'm reasonably acquainted with the Cura innards and I don't believe that to be the case. In the situations where I have seen under-extrusion in my own prints the problem has always been due to some bad combination of settings that resort in too much demand being placed on the extruder.

[Arak0n 0]

1 hour ago, burtoogle said:

Hello @Arak0n, could you please provide the project file for that print? Do File->Save and attach the .3mf file to this thread. Thanks.

 

Attached.

 

CE3_Mendel90_BFPTouch.3mf

[burtoogle 513]

Thanks for the file but, unfortunately, it wasn't a project file. Please do File->Save (not Export). Thanks.

[Arak0n 0]

Ah, sorry.

Here you go.

 

CE3_Mendel90_BFPTouch.3mf

[burtoogle 513]

Thanks for that, I'll take a look later. In the meantime, I printed your model on a Sovol SV01 (budget printer) using 0.2 layers and 0.4 nozzle, 15% gyroid infill. Took 31 mins and came out like this...

 

 

 

 

Look at the speeds, here...

 

 

The walls around the holes are printed SSLLOOWW..

 

How to get that?

 

 

One other thing. I am printing using Octoprint and in there I am specifying a flow rate of 108%. I could have specified it in the slicer but, it makes no difference. Why? Well, when I calibrated my extruder at a typical extrusion rate, it under-extruded by around 8%. The point is that you have to calibrate your extruder using a realistic feedrate and temperature for the material in use. It's not good calibrating your extruder without actually pumping plastic at a typical rate. Some firmwares (e.g. RepRap) can do non-linear extrusion which is nice but, otherwise, you just have to pick a suitable flow rate for the target extrusion rate.

 

Hope this helps, will take a look at your project later....

 

 

 

[henderpa 0]

Perhaps "small feature speed" is the crucial factor, here. Because I've tried upping the extrusion, even just around holes or on walls, but that makes it _overextrude_ any straight lines... because the underextrusion is only happening (for me) on curves. Anyhow, thanks for the suggestion, I'll try pulling "small feature speed" way down.

[burtoogle 513]

Hi @Arak0n, I looked at  your project file. I can't see anything really obviously "wrong" but a few things I would change (personal preference only) is to disable coasting and also disable the acceleration and jerk control. I would reduce the max comb distance without retract to 10 and use the not in skin combing mode. Print the inner and outer walls at the same speed. As I mention above, it pays to slow down the walls around the small holes and, above all, make sure that at the print speeds you are using, the extruder is really pushing out the right volume of plastic. Hope this helps.

[Arak0n 0]

Thanks, I'll try those. However, what's wrong with coasting? As far as I'm aware, that should reduce blobs at the end of a line or layer change, no?

I'm not using linear advance on the printer.

 

[burtoogle 513]

27 minutes ago, Arak0n said:

However, what's wrong with coasting?

 

I like to maintain as constant extrusion pressure as possible across retracts/primes. Coasting deliberately reduces the pressure so it's going to increase the likelyhood of under-extrusion at the start of the next line. I know that you can set a prime extra amount to compensate but I'd rather not and, anyway, the extra prime doesn't occur if the travel move didn't use retraction.

[henderpa 0]

I've tried adjusting some of the settings suggested above, and I can confirm that it's not that my speeds/temps are too high. I tried a print at 190 degrees (the lowest temp advised for this particular PLA, confirmed with an external thermal sensor) and 30mm/s print speed, line width of 0.4mm and layer height of 0.2mm, no combing, no acceleration, no jerk control, etc. Still came out with crummy round inner walls and perfectly good straight inner walls. I know burtoogle is skeptical that it's anything but a setting issue, but then I really don't understand why it also happens at default Cura settings, and why it's only curved lines and not straight ones (or why it's only inner curves and not outer curves).

Also: tried a brand new hot end with a brand new nozzle, so it's not from clogging...

[henderpa 0]

Hoping the comb setting burtoogle suggests above produces a change! Trying that next...

[burtoogle 513]

And you have calibrated your extruder steps at a sensible print speed?

[henderpa 0]

36 minutes ago, burtoogle said:

And you have calibrated your extruder steps at a sensible print speed?

Thanks! I have. I did that when I switched firmware and checked it when I put on the new hotend.

[burtoogle 513]

2 hours ago, henderpa said:

190

 

That's coolish for PLA and will tend to make under-extrusion more likely. Also, try printing the small hole outlines slower, e.g. use 50% small feature slowdown to print at around 15mm/S.

[henderpa 0]

18 minutes ago, burtoogle said:

 

That's coolish for PLA and will tend to make under-extrusion more likely. Also, try printing the small hole outlines slower, e.g. use 50% small feature slowdown to print at around 15mm/S.

Thanks, I had been printing with a range of higher temps and was told the temps were abnormally high and that that was a likely cause (which didn't make sense to me, but process of elimination... I can't remember if it was this thread or another, as this topic is plastered around the Ultimaker fora). So I tried lowering it as low as I could still print, and the issue is still happening. I have also been running with a 50% small feature speed but that hasn't fixed it. At any rate, my main question is still: why is extrusion noticeably (almost unusably) worse specifically with curved holes, and only in Cura? I'm not having any other extrusion-based problems whatsoever. Not even on other (straight edged) hole-walls.

[burtoogle 513]

10 minutes ago, henderpa said:

I have also been running with a 50% small feature speed but that hasn't fixed it

You checked the layer view speed colouring to verify that those small circles are really being printed at 15mm/S ?

[henderpa 0]

15 minutes ago, burtoogle said:

You checked the layer view speed colouring to verify that those small circles are really being printed at 15mm/S ?

Yup, the walls of the holes are blue; the rest is green.

[henderpa 0]

Update—the only single setting that has worked so far to eliminate the gaps is 

On 8/20/2020 at 2:24 AM, burtoogle said:

I would reduce the max comb distance without retract to 10 and use the not in skin combing mode.

Thanks burtoogle!

I have just tested with these settings and so far they're the only thing that has gotten rid of the gaps around the holes. I just did two prints; the first one was after I'd tried a bunch of stuff and it still made swiss cheese of interior round holes. For the second print, I _only_ added comb distance without retract as 10mm and switched combing mode to not in skin. Printing the same model with only those two settings changed, and I'm not getting any problems with my round holes. They are perfect.

So... anyone willing to venture a theory as to why those two small tweaks in particular solved it when everything else I tried didn't? (I'm admittedly still cautious in my optimism, and will certainly want to reprint some old troubled models with these two things changed to see if that fixed it on them as well...)

[burtoogle 513]

4 hours ago, henderpa said:

Printing the same model with only those two settings changed, and I'm not getting any problems with my round holes. They are perfect.

 

Good, that's progress!

 

4 hours ago, henderpa said:

So... anyone willing to venture a theory as to why those two small tweaks in particular solved it when everything else I tried didn't?

 

If you're using combing you will get under-extrusion after a long (> 10mm or so) travel move unless retraction is used.