Skin separated from fill.

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Doug68
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Skin separated from fill.

Post by Doug68 » Sat Dec 10, 2016 11:44 pm

So I printed off the bit below...
Was feeling proud of finally using the full printable envelope nearly and then...
Picking it up I realise the skin is detached from the fill, for the top 6" or so, with the part being all floppy and basically no use to me unless I magically fix it some how (this after a 63 1/4 hour run :( ).

Image
IMG_20161211_110718 by Doug Clark, on Flickr

So what did I do different on this to compared other prints?
Well I've seen the print typically slowing down as it gets taller, research led me to believe this was due to the min time per layer setting which i reduced from 40 secs to 5. As a result all the outside printed at 35mm/sec and the fill at 40mm/sec.

I thought it might be due to under extruding so I checked that as per the matter hackers guide and found I was about 2% under extruding, I don't think that's enough to be the issue at this speed?

HE temp was 220c as normal
Bed temp 70c as normal
Same PLA filament as used before (3DFillies.com)

So was the extra speed enough to cause the under extrusion to get to the point where the join wasn't formed due to a lack of material and or heat?
Do I just slow it down or is there another remedy?

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Re: Skin separated from fill.

Post by Doug68 » Mon Dec 12, 2016 9:22 pm

Nothing? :(

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Xenocrates
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Re: Skin separated from fill.

Post by Xenocrates » Mon Dec 12, 2016 10:20 pm

I guess I'll chime in a bit. I've been thinking about the causes, but didn't want to say anything until I had a decent guess.

First, it's not the minimum layer time. I usually don't see it interfering until I get to rather small (inch square or so) parts.
I believe that under extrusion and gradually reduced heat from the heated bed ended up combining with a low infill overlap value. However, I have no idea if this is the actual issue.
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Re: Skin separated from fill.

Post by nebbian » Mon Dec 12, 2016 11:08 pm

I've had similar happen to me as well. In my case it was due to poor choice of extrusion widths, meaning that the calculated fill width (on a thin part like yours) was well under the nozzle width. It meant that the fill didn't join to the perimeters, and resulted in a floppy part that was internally delaminated.

In my case it was a part that looked like a squat wide tube with walls that were around 2mm thick. Looking at your part I'd guess that this is a good candidate to check.

I fixed it by fiddling with the extrusion widths and looking at the generated preview, to ensure that the fill width was at least as wide as the nozzle, ALL the way up the part.

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Re: Skin separated from fill.

Post by Doug68 » Tue Dec 13, 2016 12:38 am

Thanks All,

That helps the fill overlap setting I didn't know existed.
I'll have a bit of a fiddle with it tonight and see how I go.
The part itself is 5mm thick with 1mm walls

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Re: Skin separated from fill.

Post by Doug68 » Mon Jan 16, 2017 8:02 am

So I'm still going with this issue, I've tried quite a few different things to no effect.
Running the extrusion width exercise made me think about that some more, even though the width was coming out fine for that at ~0.5mm, I went back and pulled apart a print to measure the layer width in that and got ~0.4mm, so I set the extrusion multiplier to 1.25 and tested again.
Again the outer layers (3 layers thick) were separated and again they measured ~0.4mm wide.
Going from 1 to 1.25 on the extrusion multiplier I'd have thought I should see some difference even if the result was horrible?

So where to now...
Some sort of clog in the HE?
Extruder slipping?

Here's a picture of what it looks like pulled apart, note the inner perimeter is bonded nicely to the fill and vertically the fusion is good i think.

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IMG_20170116_221909 by Doug Clark, on Flickr

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Xenocrates
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Re: Skin separated from fill.

Post by Xenocrates » Mon Jan 16, 2017 10:50 am

Since the extrusion multiplier hasn't helped any, I might try reducing the extrusion width, or else checking the nozzle for a partial clog, more likely both, to see if there's an issue somewhere. And if the result hasn't changed at ALL, I would make sure that the changes saved and that the model actually did get resliced (especially if running from an SD card). I've seen some people tweak and tweak for 2 hours on a part that failed 5 minutes in every time, because they didn't save the new Gcode to the SD card properly, and kept loading the original code.
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Re: Skin separated from fill.

Post by Doug68 » Mon Jan 16, 2017 6:13 pm

I run the prints mostly from my PC I've found things to go wrong from the SD card with big parts for some reason, not re-tried that in some time to find out what the heck is going on with that, but back on subject.

Re-slicing, yes I checked the extrusion multiplier setting was saved etc. but its possible the model did not get re-sliced.
I'll clear it all out and start again print-wise. Think I'll knock out a shape specific for the testing, rather than keep trying with 'real' parts, hopefully that'll speed things up.

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Re: Skin separated from fill.

Post by Polygonhell » Tue Jan 17, 2017 12:34 am

Infill not reaching the wall is usually a function of backlash/slop in the system.
Given you say it's only happening at the top of the print, I'd move the hotend to a position near where it happens and give it a general wobble test, comparing how it feels in areas that do not exhibit the issue.
If it's not mechanical, you might want to try a different Slicer to see if it produces different results.
Given the size of the part it's probably not practical to print a test piece, but a simple cylinder with similar wall spacing would probably be worth printing to see if it exhibits the same issue,

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Re: Skin separated from fill.

Post by Doug68 » Tue Jan 17, 2017 6:14 am

Polygonhell wrote:Infill not reaching the wall is usually a function of backlash/slop in the system.
Given you say it's only happening at the top of the print, I'd move the hotend to a position near where it happens and give it a general wobble test, comparing how it feels in areas that do not exhibit the issue.
If it's not mechanical, you might want to try a different Slicer to see if it produces different results.
Given the size of the part it's probably not practical to print a test piece, but a simple cylinder with similar wall spacing would probably be worth printing to see if it exhibits the same issue,


The fill is attached to the first perimeter layer but the next 2 perimeter layers are not attached to each other.
By that I mean when you are looking straight down on to the print the outside 2 layers can be pulled away from the print.
I've just run another test to make sure the high extrusion multiplier setting (1.25) was used and again got the same result as when it was set to 1.
I've checked in the G code and can see the new multiplier is being used, therefore I'm guessing its something in the hardware like a blockage?

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Re: Skin separated from fill.

Post by Doug68 » Wed Jan 18, 2017 5:25 pm

I think I found the issue, I think it was a partially blocked nozzle, which might have been cause by the nozzle not being fully tight, I'm not sure how it could have come a bit undone thermal cycling I guess, but it was not properly tight and that effects the tightness of the heater block and so on.

Anyway cleaned it all out from end to end and now the thing is printing like a champ.

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Re: Skin separated from fill.

Post by Doug68 » Fri Feb 10, 2017 8:34 pm

I've still not eradicated this issue. What I think is happening is the bowden tube is gradually being pushed out of the hot end.
This then causes the plug issue and under extrusion.
I've replaced the bowden tube and gave it some extra length to ensure its not getting tugged on.
Also did the thing with the extruder top undone 2 turns, push the tube in and then tighten up the top.
I've ordered a new connector bit to got in the top of the extruder also, but that's not here yet.

On the last print it start off fine but by the end (~50 hours later) it was under extruding again.

I should have marked the tube to see if I can measure it being pushed out, that'll be the next step to clean it all up and try again.

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Re: Skin separated from fill.

Post by tehwadeski » Sat Feb 11, 2017 8:53 am

Have you seen this article regarding the proper seating of the boden tube?

https://seemecnc.zendesk.com/hc/en-us/a ... lament-JAM

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Re: Skin separated from fill.

Post by geneb » Sat Feb 11, 2017 10:40 am

tehwadeski, I think that's what he was referring to by the "extruder top undone 2 turns", although I think he's talking about the hot end.

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Re: Skin separated from fill.

Post by Doug68 » Sun Feb 12, 2017 6:04 pm

geneb wrote:tehwadeski, I think that's what he was referring to by the "extruder top undone 2 turns", although I think he's talking about the hot end.

g.


Sorry yes that correct, undoing the hot end cap 2 turns.
On assembling the last time I've use lock wire to force up the locking ring on the bowden tube, I've been suspicious of the little black flexi clip. I think if there's any play in that at all as the filament is pushed - pulled then the thing can work its way loose.

At the moment the only way I've found to deal with this is to set the nozzle diam to 0.4mm even though its not, maybe the new nozzle that's on its way will fix it.

I'm re-running the print from the first post in the thread, hopefully it'll get to the end of that without an issue as currently set.

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Re: Skin separated from fill.

Post by adarcher » Sun Feb 12, 2017 8:44 pm

If you use the new cura (2.4 beta) you can check the extra alternate wall, which alternates an extra perimeter every other layer to help attach the infill. I've found it helps make much stronger parts.

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Re: Skin separated from fill.

Post by Doug68 » Thu Feb 23, 2017 6:16 pm

I've now got a new 0.5mm nozzle (stainless) and fitted that.
So far this has fixed the issue, quite what was going on inside the old brass one that could cause it to clog I do not know. I had flamed, scrubbed it clean, I suspect repeated bashing into the glass during auto-calibration might have modified it, but that does not sound too convincing a story to me.
Onward.

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Re: Skin separated from fill.

Post by 626Pilot » Fri Mar 03, 2017 10:18 pm

Brass nozzles can get deformed if they crash into the bed multiple times.

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Re: Skin separated from fill.

Post by Doug68 » Fri Mar 10, 2017 12:44 am

626Pilot wrote:Brass nozzles can get deformed if they crash into the bed multiple times.


Ha ha, well it got smashed quite a few times whilst I was on the steep part of the learning curve, so I guess that was it.

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