ABS filament getting 'stuck' about 20 min into a large print.

Hi,

New to the 3d printing world and I just finished a Sintron 3d Prusa i3 kit. Trying to get ABS printing working.

I have a fairly ornate model (Slic3R estimates 14hours) that I need to print and I have been running into a couple of problems very consistently. It is about 170mm by 100mm and 150mm high.

I'm running the heat end at 240 with black ABS. I slowed down the print speed for the perimeter and support printing to 30mm/s after running into some consistency issues which seem to be cleared up.

I am still experiencing these two issues:

1) About 20-30 minutes into the print, I have noticed the extrusion of filament has stopped (while the printing motion is still going). Usually I find this out when it has been 1-2 hours of no filament extrusion and I have to start the print over. Once I was able to catch it when it happened - so when I pause the print, I try to wiggle and push the ABS filament down towards the hot end to get it to ooze - and it felt'stuck' where I have to reverse it back 5-8mm and then re-feed a few times before it can 'reach' the hotend and ooze a bit. Note that when this happens it is still inside of the threaded shaft immediately before the nozzle - like it is getting stuck inside (forgive me I don't know the proper name). I am not sure why it is stopping in this 20-40 minute window, but it is consistent. Curiously, smaller prints are just fine. I was wondering should the extruder fan be running 100% of the time or only partially or not at all? I wonder if there is a hardening/cooling issue inside of the threaded shaft just before the hot end.

2) I notice than when it is printing the skirt, which I made the height of the object, the extrusion material only seems to come out at certain parts of the 'wall' being formed - 2 opposite corners end up stringy and flimsy and 2 other corners of the skirt seem consistently printed.

I would welcome any feedback on this issue.

Thanks so much in advance.

Steve

Edited 2 time(s). Last edit at 05/24/2015 05:46PM by stevemeetswest.

1. With most types of print head, the hot end fan must run continuously to cool the heatsink at the top of the nozzle assembly. This fan is normally wired directly to 12V so that it runs whenever the machine is turned on. Make sure it doesn't also blow air on the print when you are printing ABS.

2. Common causes of feed failures include:

A. Hot end becoming blocked by a plug of plastic, caused by insufficient cooling, missing PTFE liner, excessive and frequent retraction, or bad hot end design.

B. Nozzle gets temporarily obstructed due e.g. to an overhang curling up, then the extruder drive grinds away some of the thickness of the filament, causing it to lose grip even when the nozzle is no longer obstructed. Fix is to reduce extruder motor current so that the motor skips steps instead of grinding the filament.

C. Overheating extruder motor driver.

D. Too little extruder motor current.

E. Hobbed insert clogged.

3. Your problem with the skirt suggests to me that either the bed is not level and is twisting slightly as it moves along the Y axis, or you are using auto bed compensation but it is compensating by the wrong amounts.

This advice isn't specific to your particular model of printer. Someone with the same printer and hot end as you may be able to offer more specific advice.

Edited 2 time(s). Last edit at 05/24/2015 06:39PM by dc42.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

Ok, so I decided to take everything apart while the filament was stuck and I did some research on how the extruder parts fit together.

What I found was a hardened piece of ABS in the 'PTFE' tubing, towards the end with the hotend, So somehow this area was hot enough for it to melt slightly and deform the ABS and this deformation widened the ABS in the tubing and kept the ABS from reaching it's destination in the hot end.

[swindon.hackspace.org.uk]

So, now I am wondering how does this happen and how do I fix

Edited 1 time(s). Last edit at 05/24/2015 06:45PM by stevemeetswest.

Hi - thanks for the quick reply - it was definitely 'A' - some deformed/hardened ABS in the PTFE liner. I am a bit confused though if the issue is that it is heating up there when it should not - almost as if the heat is travelling too far back 'up' the barrel and melting more than it should?

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stevemeetswest
Hi - thanks for the quick reply - it was definitely 'A' - some deformed/hardened ABS in the PTFE liner. I am a bit confused though if the issue is that it is heating up there when it should not - almost as if the heat is travelling too far back 'up' the barrel and melting more than it should?

Can you confirm that the hot end fan is running continuously, is blowing air the right way, and the air is directed over the heatsink? What type of hot end is it?

[EDIT] Also, what are your retraction settings?

Edited 1 time(s). Last edit at 05/24/2015 07:00PM by dc42.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

Yes - I can confirm the fan - as I manually set it to be on while I was troubleshooting. With that said, I did read somewhere it should be on 'for a while' after a print has stopped so it can cool down the parts.

I am using an MK8 extruder.

I stumbled on something just now in regards to the retraction - so I checked my retraction points and sure enough they are immediately before the 'weak' parts of the skirt wall.

I changed my default settings from 30mm/s in speed and 500mm/s acceleration to 10mm and 300mm respectively - printer is warming up now and I am going to give it a shot again.

Quote

manually set it to be on

Sounds like you connected it to the 'fan' output of your controller board. That connector is intended for a print cooling fan(s) and isn't a great place to connect the hotend/coldend fan, even though it seems like the obvious thing to do with most Prusa kits only having one fan supplied and a big connector marked 'fan' begging to have something connected to it. As dc suggested, connecting it directly to 12v power is your safest bet. Depending on your software config the 'fan' output may not be supplying it's maximum potential output, and will at the very least have a mosfet forward voltage drop on it. If you want to get fancy you can configure Marlin to use a spare pin to control the hotend fan and only run it when the hotend is heated, but to start with, simple is good.

James

Try reducing your retraction distance... I recently switched from a Ubis hotend to a Chinese E3D V6, and had to reduce the retraction distance from 4.5mm (the Cura default) to 0.5mm.

I think what's happening is that when the extruder retracts, it pulls some molten plastic back into the cool part of the heat break (the pipe connecting the heated block to the heatsink). If that plastic sits there too long, it spreads out and solidifies and sticks to the sides, strong enough that the extruder can't push it back down into the hot part again.

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stevemeetswest
I'm running the heat end at 240 with black ABS.

For kicks and giggles, try another color. Black filament is the industry's dumping ground for floor sweepings, regrinds, and anything else that they can try to use as filler in place of raw plastics. Not saying they all do this, but it is a standard warning any time someone has jamming problems with black filament.

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stevemeetswest
What I found was a hardened piece of ABS in the 'PTFE' tubing, towards the end with the hotend, So somehow this area was hot enough for it to melt slightly and deform the ABS and this deformation widened the ABS in the tubing and kept the ABS from reaching it's destination in the hot end.

[swindon.hackspace.org.uk]

If that is the exact hotend in use, it does not appear to have an adequate thermal heat break between the heater block and the heat sink. When the cooling fins reach the temperature where plastic turns rubbery, the filament expands out and grabs the inside walls of the tube. Look at the E3D design, where they use a tiny stainless steel heat break (because it is a poor conductor of heat). Even with that, they still need a fan on the hear sink or the heat creeps up into the fins and causes jams.....

Thanks for all the feedback. So I tried a few things and I am quite convince I have a heat creep issue, but I am still not sure how to resolve it.

- Tried a new transparent filament from a different manuf - and it works far better for a longer time then black. It still failed (stopped extruding) about 1.5 hours into a 4 hour print.

- I have taken apart and rebuilt the components of the MK8 just to be sure everything is connected and seated properly.

- I did move the power for the extruder fan to the 12v terminals so it is on when the printer is on. The end result is when the hot end is at 230c - i can touch the heatsink and surrounding area with no problem - only slightly warm.

When the extrusion stops, if I pause the print I can manually push the filament down past whatever blockage down to the nozzle - at which time it resumes extruding on its own but only for a short while.

I don't know what to try at this point - I know it is a heat issue but it seems like I am setup like everyone else.

[i01.i.aliimg.com]

The only thing I have changed that I didn't think would matter is the fan. I accidentally broke one of the blades and so I replaced the fan with this one:

[www.amazon.com]

I have left the temp at 230c. Any suggestions would be welcome.

Steve

Hi Steve,

exactly what happens when the filament fails to extrude? Does the extruder fail to turn (the stepper motor stalls & clicks, or maybe just stops without any noises) or does the motor keep turning and the filament slips? If you can push the filament through the blockage by hand then it suggests your extruder isn't producing enough force. If the motor stalls then you need to check the driver current - it might be too low and not generate enough torque (clicks) , or too high and overheating the driver (silent stop - I think, never actually seen it happen). If the motor keeps going but the filament slips then try tightening the tension adjustment screw to squeeze the filament harder.

What retraction settings are you using? You could try turning retraction off entirely as a test.

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stevemeetswest
The only thing I have changed that I didn't think would matter is the fan. I accidentally broke one of the blades and so I replaced the fan with this one:

[www.amazon.com]

The fan above is rated for 4.1 CFM. Amazon has others that are rated for 6+ CFM. Hint - "silent" fans usually don't move as much air as "loud" fans.....

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JamesK
Hi Steve,

exactly what happens when the filament fails to extrude? Does the extruder fail to turn (the stepper motor stalls & clicks, or maybe just stops without any noises) or does the motor keep turning and the filament slips? If you can push the filament through the blockage by hand then it suggests your extruder isn't producing enough force. If the motor stalls then you need to check the driver current - it might be too low and not generate enough torque (clicks) , or too high and overheating the driver (silent stop - I think, never actually seen it happen). If the motor keeps going but the filament slips then try tightening the tension adjustment screw to squeeze the filament harder.

What retraction settings are you using? You could try turning retraction off entirely as a test.

Hi there, The motor turns and grinds on the filament. I have tried adjusting the tension - and actually watched it with the heatsink/fan off to make sure I had it set tight but not too tight.

I have also at this point disabled the retraction altogether.

You have a point though - if I am able to push it down (with force) perhaps there is some other way to have a better 'grip' on the filament?

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stevemeetswest
Hi there, The motor turns and grinds on the filament.

If you think you have the tension right, then I suggest you reduce the motor current so that it skips steps rather than grind on the filament. That way, if the nozzle becomes temporarily obstructed, extrusion will continue when the obstruction is removed. I had a big problem with extrusion failing until I reduced the motor current on my Mini Kossel form 800mA to 500mA.

Edited 1 time(s). Last edit at 05/25/2015 06:27PM by dc42.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

That's one thing I don't remember having read about - how do you judge how much tension to put on the extruder? What constitutes too much tension?

What kind of hot-end are you using? Some are more jam-prone than others.

I disagree with the Fan always on concept. I let Repetier control the fan during my prints and I do not get jamming (anymore). I don't want the fan on during the first layer. Here is how the automated process goes with Repetier, and Prontrface:

This is the process that works for me without fail now:

Load STL.
Select print settings (layer height, speed, infill)
Slice
Hit print
Software will heat up the bed first
Then it will heat up the hot end
Prints the first layer with hotend fan off (hotend fand connected to D9 middle two connectors between bed and hotend power out. (*assuming ramps 1.4*)
Turns on Fan to set speed (mine is 50%) for the duration. I've noticed it will turn off the fan during infill and on during peremiters.

This is the process that was causing me the most jams:
Load STL
Preheat hotend
Preheat bed
Hit print
This would have the fan off during heating and always caused heat creep. It is also the worst way to start a print.

Now, I just let the software do it for for me. Those developers are smart cookies.

Edited 2 time(s). Last edit at 05/26/2015 12:33AM by thetazzbot.

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thetazzbot
I disagree with the Fan always on concept.

Different fan, I think. The hot-end fan, blowing air onto the fins of the heat sink, should be on all the time. The nozzle fan, blowing air onto the newly extruded filament, should be off for the first layer, then on as you described.

Frank

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JamesK
That's one thing I don't remember having read about - how do you judge how much tension to put on the extruder? What constitutes too much tension?

I have been eye-balling the gear and the bearing. If too tight you will see the bearing stop and start where as just the right pressure the bearing is in line with the gear movement.

So........

I am pleased to report I got this working. I changed 2 things before it started working again.

1) I took apart the extruder once more and positioned the heater barrel so it was more inside of the cold end - closer to the extruder gear. I was able to get the heater barrel to about 1-2 mm distance from the extruder gear. I figured that this way more of the barrel would be subject to the cooling.

2) I had stumbled on some articles claiming raising the temperature for ABS into the 260+ range has helped a bunch, so I adjusted my temp to 265c (previously 230c)

After these two changes, I have been able to have 2 prints totalling 16 hours with full extrusion - no interruptions or skips whatsoever.

I haven't taken the time to try a long print at 230c to see if it was just moving the barrel up further that fixed it - but for now I am back in business - thanks for all the suggestions and help!

- Steve

Edited 2 time(s). Last edit at 05/26/2015 07:24PM by stevemeetswest.