What caused this issue?

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What caused this issue?

Postby plexus » 2014-Mar-Wed-14-Mar

PLA, 500µm layers, 60 mm/s print speed

The issue has been solved. Can you determine the solution?
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What caused this issue?

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Re: What caused this issue?

Postby Stradawhovious » 2014-Mar-Wed-15-Mar

I don't really know being a rank noob and all, but if I had to guess I'd say failing hotend thermistor?
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Re: What caused this issue?

Postby plexus » 2014-Mar-Wed-15-Mar

Stradawhovious wrote:I don't really know being a rank noob and all, but if I had to guess I'd say failing hotend thermistor?


can you explain why you think this?
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Re: What caused this issue?

Postby Stradawhovious » 2014-Mar-Wed-16-Mar

plexus wrote:
Stradawhovious wrote:I don't really know being a rank noob and all, but if I had to guess I'd say failing hotend thermistor?


can you explain why you think this?



Kind of...

Here goes. It looks like at some point in the last layer of the print the temp was dramatically raised. I'm making that assumption because in spots closest to the camera it appears that the material was too hot and poured out and dragged around rather than nicely laid down by the extruder like the rest of the print. This leads me to believe there was a temp spike. In my limited knowledge of this outside of a malfunction this would have to be programmed in or manually input by the user. The only thing I can think of that would cause this in a malfunction would be the thermistor giving a false low temp.


Knowing that I'm not afraid to look stupid on the interwebz, how far off am I? (not looking for you to disclose an answer, just looking for a hot/cold... no pun intended)
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Re: What caused this issue?

Postby evanalmighty » 2014-Mar-Wed-16-Mar

Looks like layer height is too high. The layers aren't adhering well to each other. That or the extrusion rate is too low.
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Re: What caused this issue?

Postby Stradawhovious » 2014-Mar-Wed-17-Mar

evanalmighty wrote:Looks like layer height is too high. The layers aren't adhering well to each other. That or the extrusion rate is too low.


That's probably a far more reasonable theory than mine. Hard to consider a cause when you aren't watching the print.
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Re: What caused this issue?

Postby RetireeJay » 2014-Mar-Wed-17-Mar

This is a tough one.

The perimeters look perfect all the way to the top. And the infill toward the back left corner looks fine. But the infill toward the front right corner gets progressively worse and worse. And the problem goes down many layers below the top layer. So it's not a problem with the thermistor or temperature regulation of the head suddenly going awry because it repeatedly happened layer after layer in just a particular part of the geometry.
I'm leaning toward something physically near either the back left or the front right corner causing a pretty strong gradient, like a fan or a source of heat that is not tied to the extruder but is stationary relative to the moving printhead.

But truthfully I'm stumped.

EDIT: A 500 micrometer layer is 0.5mm, which is pretty thick. Were you using a nozzle at least 0.6mm in diameter? I guess trying to print a thick layer with a nozzle that's too small might cause some strange problems.
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Re: What caused this issue?

Postby redwood » 2014-Mar-Wed-17-Mar

The G code got corrupted?
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Re: What caused this issue?

Postby plexus » 2014-Mar-Wed-22-Mar

I am using a 0.6mm nozzle E3D hot end. it will actually even do down to 0.1mm layers pretty nicely although not as good as a narrower nozzle.

You can rule out the thermistor because you can see the problem occurs many layers down and if the thermistor were not working you would expect it to affect the whole print. or if it malfunctioned later in the print, there wouldnt be an issue with the lower layers.

This print was stopped before it finished after seeing the issue. That's why you can see the infill.

The print bed was levelled with the nozzle.

Gcode was fine.

There is nothing around the printer that changes airflow or temperature differently in one place vs another.
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Re: What caused this issue?

Postby Lemm » 2014-Mar-Thu-05-Mar

I had some issues which looks a bit like yours. When I fully extend my y axis the head swings a bit and make a crappy infill. I know you have a plus or lc so the head should not swing but maybe the hotend does when it's not tight. So the perimeters were clear cause the slower printspeed but the infill could become crappy
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Re: What caused this issue?

Postby DonaldJ » 2014-Mar-Fri-14-Mar

With that kind of infill you're actually bridging between the layers, so I would check those settings.

I prefer the honeycomb infill myself. Slower and uses more filament, but much more robust infill. 10 per cent or less is usually very acceptable, depending on the object.
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Re: What caused this issue?

Postby plexus » 2014-Mar-Fri-20-Mar

They way I solved the problem was to first consider obvious things. to me that was bed leveling. but that didnt help. next i considered the filament getting restricted as the extruder move to the right (filament was on the left) but that wasnt it. then i considered what has changed. i removed the fan. replacing the fan fixed the problem 100% completely as the infill printed even and shiny across the whole interior. never would have thought that would make such a difference. im still trying to sort out why. any ideers?
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Re: What caused this issue?

Postby RetireeJay » 2014-Mar-Fri-21-Mar

Umm... So you removed the fan and the print went bad. You put the fan back on and the print got good again. And you wonder why. Are you saying that when you put the fan back on it was mounted but not running? Because it would seem pretty obvious that if the fan is mounted and running it's for sure going to make a difference!
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Re: What caused this issue?

Postby plexus » 2014-Mar-Fri-21-Mar

We know that a fan helps. I have done numerous prints without a fan that worked out great, PLA, ABS, Nylon etc. I use the fan judiciously, or I used to, because I found sometimes it mattered and sometimes it didn't. But these days I just run it all the time because I have not found that it hurts. it either helps or has no effect. So this was a print that I didn't think a fan would make a difference on, but it did.

Why?

Do you know why a fan matters? we know that a fan helps. but do we know why? for example that infill... why does running a fan on it as it prints make such a difference? with PLA. with ABS it doesn't have much of an effect - the ABS will infill fine with or without.

So yes, I am wondering why? like the actual physical/chemical/mechanical reasons why it matters.
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Re: What caused this issue?

Postby DonaldJ » 2014-Mar-Sat-05-Mar

Seems to me that it has to do with the glass transition characteristics of PLA. Hot PLA seems "droopier" to me than hot ABS and the fan keeps it from sagging.

But too much fan and layer adhesion gets lousy, in my experience.
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Re: What caused this issue?

Postby plexus » 2014-Mar-Sat-12-Mar

ah yes, of course! PLA can get very watery too. that makes sense... the fan cools the extrusion as it comes out of the nozzle solidifying it to some degree making it stiffer so that it will bridge across and not just fall apart as it did in my print. i think you are right, DonaldJ. so many variables...
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Re: What caused this issue?

Postby DonaldJ » 2014-Mar-Sat-17-Mar

Variables, indeed.

I've given up on the quest for the perfect print. If the part functions as required and the layers don't separate, I'm a happy camper. I don't mind a little post processing with sandpaper, Dremel, or whatever. It's rapid *prototyping*...

I like fat nozzles, thick layers, and short printing times; works very well for the stuff I'm interested in.
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Re: What caused this issue?

Postby plexus » 2014-Apr-Tue-15-Apr

I wish clients that pay me to work on their prototypes and print them would be as forgiving as you. they don't like the visibility of the layers and other plastic anomalies caused by the printing process. oh well. but I have to try and get the best quality out of the printer for them otherwise its hard for customers to justify the cost. yes they know its a prototype but they don't care. they want it to look as good as possible. often they are using the prototypes as a way to secure interest in their project.
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Re: What caused this issue?

Postby spaceorange12 » 2014-Sep-Wed-19-Sep

I think it might be drive gear or hobbed bolt slippage. I had a similar issue, where certain areas came out funky, and I fixed it when I cleaned out the drive gear. If there is plastic jammed into the notches, the filament will routinely "skip" that part of the gear, so the issue is repeated each time the gear circles around. If you live in a hot and/or humid area, it is more likely because it softens up the plastic, which helps it squish into the notches.
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