Inconsistent extruder feed, jams - tried new hotend with no luck
Posted by geemoto
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Re: Inconsistent extruder feed, jams - tried new hotend with no luck June 21, 2015 09:52PM |
Registered: 9 years ago Posts: 70 |
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Re: Inconsistent extruder feed, jams - tried new hotend with no luck June 21, 2015 09:57PM |
Registered: 9 years ago Posts: 1,873 |
It's kind of difficult to tell from the photo - can you see where the gap starts and stops? If it's the extruder then the start/stop would probably be random compared to x/y, but as far as I can see the missing filament seems to always be for a complete layer. That almost suggests a Z axis problem rather than the extruder?
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Re: Inconsistent extruder feed, jams - tried new hotend with no luck June 21, 2015 09:59PM |
Registered: 9 years ago Posts: 70 |
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JamesK
It's kind of difficult to tell from the photo - can you see where the gap starts and stops? If it's the extruder then the start/stop would probably be random compared to x/y, but as far as I can see the missing filament seems to always be for a complete layer. That almost suggests a Z axis problem rather than the extruder?
It's hard to say, it looks like either the z-axis moved too far or the extruder wasn't extruding enough for that layer. I didn't think it was a Z issue because 0.3mm layers print no problem, but I guess it's a possibility.
Edit: on second glance, it really seems like full layers are missing. So the Z-axis is probably a reasonable suspect. No idea what to try for that though =/
Edited 1 time(s). Last edit at 06/21/2015 10:09PM by geemoto.
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Re: Inconsistent extruder feed, jams - tried new hotend with no luck June 21, 2015 10:26PM |
Registered: 9 years ago Posts: 1,873 |
OK, so here's a really tough thing to try and work out - can you count layers and see if the missing layers are preceded by one or more squashed together layers? That might indicate that your z axis is binding. How thin a layer are you using, and more interesting, how many steps does that work out to?
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Re: Inconsistent extruder feed, jams - tried new hotend with no luck June 21, 2015 10:33PM |
Registered: 9 years ago Posts: 70 |
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JamesK
OK, so here's a really tough thing to try and work out - can you count layers and see if the missing layers are preceded by one or more squashed together layers? That might indicate that your z axis is binding. How thin a layer are you using, and more interesting, how many steps does that work out to?
I'll give it a shot tomorrow with bright daylight, I don't know if my eyes are up to the task though
The problem starts at 0.2mm (barely) and is quite noticeable at 0.1mm(the resolution of the picture I posted). I don't think the z-axis is binding though, I would probably hear that. I have 4000 steps/mm and the layers are 0.1mm so it's exactly 400 steps.
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Re: Inconsistent extruder feed, jams - tried new hotend with no luck June 21, 2015 10:38PM |
Registered: 9 years ago Posts: 1,873 |
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Re: Inconsistent extruder feed, jams - tried new hotend with no luck June 22, 2015 10:39AM |
Registered: 9 years ago Posts: 70 |
Yep, I'm at a loss. If the layers were sticking together, I could believe the stepper was skipping steps, but is it possible for the stepper to take too many steps?
Could it just be run of the mill z-axis wobble? =/ I have the thing tightened down pretty good with Z-stabilizers, barely moves when I force it. The threaded rods are M3 as well so they shouldn't force the axis too much. The belts are pretty tights, they make a nice guitar string sound when plucked.
I don't know if this is relevant, but the first 1cm seems pretty good, and then after that the problems start.
Could it just be run of the mill z-axis wobble? =/ I have the thing tightened down pretty good with Z-stabilizers, barely moves when I force it. The threaded rods are M3 as well so they shouldn't force the axis too much. The belts are pretty tights, they make a nice guitar string sound when plucked.
I don't know if this is relevant, but the first 1cm seems pretty good, and then after that the problems start.
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Re: Inconsistent extruder feed, jams - tried new hotend with no luck June 22, 2015 10:48AM |
Registered: 9 years ago Posts: 1,873 |
Ah - do you use any sort of Z hop/Z raise between layers? Everything you describe makes me think of a binding Z axis, and if it hops up between layers it might not always come back down again under gravity. I'd be very tempted to disconnect the threaded rods and see how easily the Z axis runs (without changing anything else, like the X-axis belt tension). If there is no Z hop then I'd have to invoke a lot of flex in your frame or threaded rods to explain how the axis could stick and then pop up under elastic force. Random extra steps aren't impossible, but much more of a stretch. You'd need something like an intermittent connection of the micro-stepping jumpers, or random weirdness on the part of the microcontroller. Stuff happens, but simple mechanical explanations are usually going to be more likely.
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Re: Inconsistent extruder feed, jams - tried new hotend with no luck June 22, 2015 10:54AM |
Registered: 9 years ago Posts: 70 |
Nope, no z-hop (I assume this is lift-Z in retraction settings in slic3r). When the Z-axis isn't energized I can turn them quite easily with my hand, just a tap with my finger is enough.
I don't buy that it is the belt tension, because an entire layer seems missing, rather than just a misalignment on either the X or Y faces.
I agree that having some sort of elastic force in the frame is unlikely, it's pretty rigid. Not a metal frame but a ~0.8mm thick acrylic frame with M8 Z-frame stabilizers (Prusa i3).
I'm out of ideas for things to test.
I don't buy that it is the belt tension, because an entire layer seems missing, rather than just a misalignment on either the X or Y faces.
I agree that having some sort of elastic force in the frame is unlikely, it's pretty rigid. Not a metal frame but a ~0.8mm thick acrylic frame with M8 Z-frame stabilizers (Prusa i3).
I'm out of ideas for things to test.
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Re: Inconsistent extruder feed, jams - tried new hotend with no luck June 22, 2015 11:04AM |
Registered: 9 years ago Posts: 1,873 |
The reason I mentioned the belt tension is that on a standard Prusa the X axis belt tension can be transmitted to the Z bearings. Over-tensioning the x axis is a classic way of causing the Z to bind, as is getting the two threaded rods out of step. Still - the mystery continues!
Any chance of capturing the problem on video? That might give someone the insight they need to help. Might be tricky to get a good view though. We'd probably need a good view of the print head, the Z motors and the nuts where the Z threaded rods connect to the X axis, all at the same time!
Any chance of capturing the problem on video? That might give someone the insight they need to help. Might be tricky to get a good view though. We'd probably need a good view of the print head, the Z motors and the nuts where the Z threaded rods connect to the X axis, all at the same time!
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Re: Inconsistent extruder feed, jams - tried new hotend with no luck June 22, 2015 11:07AM |
Registered: 9 years ago Posts: 70 |
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Re: Inconsistent extruder feed, jams - tried new hotend with no luck June 22, 2015 06:59PM |
Registered: 9 years ago Posts: 70 |
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JamesK
Any chance of capturing the problem on video? That might give someone the insight they need to help. Might be tricky to get a good view though. We'd probably need a good view of the print head, the Z motors and the nuts where the Z threaded rods connect to the X axis, all at the same time!
Is there a benefit to having them all in view together rather than in separate prints? It'll be hard to get a good view of all of them simultaneously. I'm upload a video of just the print now, I'll add it to this comment shortly.
Edit: here's the video, it starts to skip about halfway through. 0.2mm layer height 200C [www.youtube.com]
Edited 1 time(s). Last edit at 06/22/2015 07:49PM by geemoto.
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Re: Inconsistent extruder feed, jams - tried new hotend with no luck June 22, 2015 09:53PM |
Registered: 9 years ago Posts: 70 |
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Re: Inconsistent extruder feed, jams - tried new hotend with no luck June 22, 2015 10:09PM |
Registered: 9 years ago Posts: 1,873 |
Wow, that's really strange. It sure starts off nice, and the speeds look very moderate. It's obviously a single perimeter wall, so what's actually in those gaps? There must be something or it would just fall apart. Is it that the filament has just changed colour, or become more transparent, or is there actually much less of it? As far as I can tell from the video the head movements don't look any different in the good areas and the bad. Does the extruder temperature vary much during the print?
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Re: Inconsistent extruder feed, jams - tried new hotend with no luck June 22, 2015 11:06PM |
Registered: 9 years ago Posts: 70 |
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JamesK
Wow, that's really strange. It sure starts off nice, and the speeds look very moderate. It's obviously a single perimeter wall, so what's actually in those gaps? There must be something or it would just fall apart. Is it that the filament has just changed colour, or become more transparent, or is there actually much less of it? As far as I can tell from the video the head movements don't look any different in the good areas and the bad. Does the extruder temperature vary much during the print?
I didn't notice during that particular print, but it seems that they're usually +/- 2C. There's still filaments in those 'weird' looking areas, it's just not aligned with the outer 'true' perimeter. I thought it might be Z-wobble so I wrapped some electrical tape around my threaded rod and reattached the coupler to allow some wiggle and tightened down my frame even further. Still no help. I've attached some more pics of the build in case it may provide some more insight.
This problem has been off and on, at one point it was printing perfectly (I'm not too sure why, it seemed almost random). Then, it started printing poorly again and I assumed it was wobble so bought some stabilizing rods. Then I thought it was the extruder so replaced the hot end. Now, I'm back to not really being sure.
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Re: Inconsistent extruder feed, jams - tried new hotend with no luck June 23, 2015 08:29AM |
Registered: 9 years ago Posts: 1,873 |
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Re: Inconsistent extruder feed, jams - tried new hotend with no luck June 23, 2015 08:47AM |
Registered: 9 years ago Posts: 70 |
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Re: Inconsistent extruder feed, jams - tried new hotend with no luck June 23, 2015 08:48AM |
Registered: 9 years ago Posts: 344 |
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Re: Inconsistent extruder feed, jams - tried new hotend with no luck June 23, 2015 11:08AM |
Registered: 9 years ago Posts: 70 |
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cristian
If you try to pull and release the wires of the thermistor repeatedly during the print (without damaging them of course), does the temperature read change abruptly?
I'll give it a shot this evening. Another thing that has come up, could it be backlash: [reprap.org]
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Re: Inconsistent extruder feed, jams - tried new hotend with no luck June 23, 2015 12:36PM |
Registered: 9 years ago Posts: 344 |
If you clearly noticed that the filament stopped flowing from time to time, then it is not backlash.
Moreover, backlash is not "cumulative" in the sense that if at some point you have some apparently missing extrusion, at some other point you must have an excess of extrusion that compensates for that, and according to your description this is not the case.
Moreover, backlash is not "cumulative" in the sense that if at some point you have some apparently missing extrusion, at some other point you must have an excess of extrusion that compensates for that, and according to your description this is not the case.
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Re: Inconsistent extruder feed, jams - tried new hotend with no luck June 23, 2015 12:43PM |
Registered: 9 years ago Posts: 70 |
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cristian
If you clearly noticed that the filament stopped flowing from time to time, then it is not backlash.
Moreover, backlash is not "cumulative" in the sense that if at some point you have some apparently missing extrusion, at some other point you must have an excess of extrusion that compensates for that, and according to your description this is not the case.
Based on your description, that does seem to be the problem. There is a region of layers that seem to be either misaligned or underextruded, and then another region that seems OK, and this repeats. It could still be the extruder under-extruding for those regions (see attached picture).
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Re: Inconsistent extruder feed, jams - tried new hotend with no luck June 23, 2015 12:55PM |
Registered: 9 years ago Posts: 344 |
Looks like jamming, so it may be any of the problems previously mentioned. You already excluded some of them, the next to try is for sure temperature.
To do that, I usually connect another thermistor to the board and I make it slide inside the hotend in the place of the filament. Then I make a dry print to see if the two thermistors give consistent reads during the whole print. It is not a 100% sure procedure but it can spot some faulty wiring/thermistors.
To do that, I usually connect another thermistor to the board and I make it slide inside the hotend in the place of the filament. Then I make a dry print to see if the two thermistors give consistent reads during the whole print. It is not a 100% sure procedure but it can spot some faulty wiring/thermistors.
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Re: Inconsistent extruder feed, jams - tried new hotend with no luck June 23, 2015 01:06PM |
Registered: 9 years ago Posts: 70 |
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cristian
Looks like jamming, so it may be any of the problems previously mentioned. You already excluded some of them, the next to try is for sure temperature.
To do that, I usually connect another thermistor to the board and I make it slide inside the hotend in the place of the filament. Then I make a dry print to see if the two thermistors give consistent reads during the whole print. It is not a 100% sure procedure but it can spot some faulty wiring/thermistors.
That'll be difficult, I don't know if I can jam another thermistor into the hotend without it getting stuck. I posted the temperature profile, does it seem suspicious?
I guess I could take the hexagon apart, but I don't know if I'd really be able to see any obstructions by eye.
Edit: I take a reading every 100ms for the extruder and average 8 readings (in the sprinter firmware).
Edited 3 time(s). Last edit at 06/23/2015 01:11PM by geemoto.
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Re: Inconsistent extruder feed, jams - tried new hotend with no luck June 23, 2015 02:09PM |
Registered: 9 years ago Posts: 344 |
If the fan is blowing constantly and you correctly tuned PID parameters, the graph looks suspicious to me. There is something wrong with either temperature or its detection in my opinion. Or your thermistor is very, very imprecise but accurate (unlikely).
I had an issue with wrong temperature detection once, and in the end I had to re-wire the thermistor: temperature reads were drifting by 20-30 degrees, but the graph of course did not show it because of PID corrections. Besides jamming, the problem is that if the temperature is drifting a lot and you don't notice, you may melt something near or inside the hotend.
I had an issue with wrong temperature detection once, and in the end I had to re-wire the thermistor: temperature reads were drifting by 20-30 degrees, but the graph of course did not show it because of PID corrections. Besides jamming, the problem is that if the temperature is drifting a lot and you don't notice, you may melt something near or inside the hotend.
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Re: Inconsistent extruder feed, jams - tried new hotend with no luck June 23, 2015 02:30PM |
Registered: 9 years ago Posts: 70 |
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cristian
If the fan is blowing constantly and you correctly tuned PID parameters, the graph looks suspicious to me. There is something wrong with either temperature or its detection in my opinion. Or your thermistor is very, very imprecise but accurate (unlikely).
I had an issue with wrong temperature detection once, and in the end I had to re-wire the thermistor: temperature reads were drifting by 20-30 degrees, but the graph of course did not show it because of PID corrections. Besides jamming, the problem is that if the temperature is drifting a lot and you don't notice, you may melt something near or inside the hotend.
Hmm, that's interesting. I could take the bed thermistor and kapton tape it to the hotend, it probably won't read the same temperature - but at least it should remain stable. I'm wary of suspecting the thermistor/hotend/heater cartridge because they were just changed and I was having the similar problems with my old one as well. I could try to tune the PID again, maybe the settings aren't optimal. The cooling fan is always on, but the nozzle fan may be turning on and off.
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Re: Inconsistent extruder feed, jams - tried new hotend with no luck June 23, 2015 02:37PM |
Registered: 9 years ago Posts: 344 |
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Re: Inconsistent extruder feed, jams - tried new hotend with no luck June 23, 2015 02:40PM |
Registered: 9 years ago Posts: 70 |
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cristian
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geemoto
but the nozzle fan may be turning on and off.
May you produce the same graph with the nozzle fan also constantly on (or off)?
It is not optimal for printing quality, but it may remove some noise from the graph.
Sure, I'll give it a shot tonight. The object that was being printed was pretty homogeneous with no bridging gaps, so turning on and off may have been an overstatement. It is more likely that it could have turned on at some point during the print and stayed on for the duration.
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Re: Inconsistent extruder feed, jams - tried new hotend with no luck June 23, 2015 05:19PM |
Registered: 9 years ago Posts: 344 |
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geemoto
Hmm, that's interesting. I could take the bed thermistor and kapton tape it to the hotend, it probably won't read the same temperature - but at least it should remain stable.
I overlooked this sentence.
First, if you chose the bed thermistor beware that you may trigger a MAXTEMP for the bed, depending on your firmware settings. In that case, either you increase MAXTEMP in the firmware or rather you attach the thermistor as if it were in a second hotend.
Then, If you stick the thermistor externally, there might be considerable difference with respect to the other one, even of the order of 20 degrees or more, depending on how well it is touching and how well you isolated it with kapton (you may also consider using some aluminium foil to wrap it before kapton). It will be very sensitive to air fluxes, so it may be stable or not. But of course it is the easiest thing to try: if you see that the temperature is stable enough on that thermistor, then you can exclude temperature as a cause of the problem. Conversely, if the reads are not stable, you still won't know whether you can exclude temperature or not.
Good luck!
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Re: Inconsistent extruder feed, jams - tried new hotend with no luck June 23, 2015 05:24PM |
Registered: 9 years ago Posts: 70 |
I realized that I actually have the extruder output data as well, so we'd be able to see if the extruder was simply outputting more power to compensate for the temperature swings, it doesn't seem to be the case - at least not to a huge degree
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Re: Inconsistent extruder feed, jams - tried new hotend with no luck June 23, 2015 05:27PM |
Registered: 9 years ago Posts: 344 |
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geemoto
I realized that I actually have the extruder output data as well, so we'd be able to see if the extruder was simply outputting more power to compensate for the temperature swings, it doesn't seem to be the case - at least not to a huge degree
Too noisy to tell...
BTW, what nozzle diameter are you using?
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