PLA random skipping mid print; hours spent troubleshooting

Hello everyone,

I have had my prusa i2 up and running for some time now, getting great prints out of it however recently I have come across a problem I can not solve.

After about 20 layers or so, the filament begins to "skip" or print in "dashed-like" lines. At first I thought this was a temperature problem, but im working at 192C at the extruder and 60-70C at the bed printing PLA only. I thought there was too much cooling involved so I removed that factor, and still the same problem.

I began investigating the effect of filament tension betweent the spool and the extruder, eliminating any tension that may exist, feeding the filament straight into the extruder, and still the problem exists. Using Prontrface to manually extrude the plastic never poses an issue! This seems to only happen while printing. Adjusting the print height seems to have no effect either, once the filament starts skipping it continues to skip! What a waste of plastic....

I am starting to think perhaps.. it could be the stepper-motor getting to hot? But to the touch the motor is only slightly warm..

Does anyone have any suggestions to why this is happening? I have tried using different colors of PLA, temperatures, spool setups etc. I have been battling this issue for some time now, I would really appreciate any help I have attached a few pictures to this post for refrence.

That looks similar to what I had with my old bad extruder. The heatshield got hotter and hotter until the extruder couldnt push enough anymore.

Some questions:

Can you easily feed filament manually into the hot end?
Could there be and obstructions in the way of the filament.
Are your esteps calibrated?
Have you tried overfeeding with 150% or similar?

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sungod3k
That looks similar to what I had with my old bad extruder. The heatshield got hotter and hotter until the extruder couldnt push enough anymore.

Some questions:

Can you easily feed filament manually into the hot end?
Could there be and obstructions in the way of the filament.
Are your esteps calibrated?
Have you tried overfeeding with 150% or similar?

Thanks for the response, Filament is easy to feed manually and comes out straight so I know there is no debris in the nozzle. I have a microfiber wrapped at the entrance of the extruder to ensure no dusts gets in.

I believe my esteps are calibrated properly. I have been rather satisfied with my prints up until now. I will try overfeeding, however this problem arose randomly. I have been printing for some time now and this never happened. Could it be due to old plastic? I usually use filament that has sat around for a while, un-packaged.

Personally I don't believe in aged filament, at least if you don't buy from a crap seller. I've got stuff that's over a year old [PLA and ABS both] and hasn't changed how it prints one bit the entire time I've printed with it.
I had problems with jamming when I switched over to my new E3D v5, if it had too many retractions in too short of a time it would jam due to thermal expansion of the PLA.
Can you move the filament by hand immediately after it jams?
Your second blue print texture, if it's not the filament, looks like the temp is too low. You can tell by texture when it looks less shiny. Some people like that texture if they have an extruder that can push out colder filament. For comparison, between different hotends I've printed PLA from 162C to 250C.

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Realizer- One who realizes dreams by making them a reality either by possibility or by completion. Also creating or renewing hopes of dreams.
"keep in mind, even the best printer can not print with the best filament if the user is the problem." -Ohmarinus

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MrDoctorDIV
Personally I don't believe in aged filament, at least if you don't buy from a crap seller. I've got stuff that's over a year old [PLA and ABS both] and hasn't changed how it prints one bit the entire time I've printed with it.
I had problems with jamming when I switched over to my new E3D v5, if it had too many retractions in too short of a time it would jam due to thermal expansion of the PLA.
Can you move the filament by hand immediately after it jams?
Your second blue print texture, if it's not the filament, looks like the temp is too low. You can tell by texture when it looks less shiny. Some people like that texture if they have an extruder that can push out colder filament. For comparison, between different hotends I've printed PLA from 162C to 250C.

I never really believed in aging filament either by means of absorbing moisture. My filament is kept in a cool dry place however, I really do not believe this is a jamming related issue. I can push through the extruder by hand, by turning the feed screw, or using prontrface to send the command. It always responds the way its supposed to. It always extrudes straight down, never to the side.

The second blue model I did start to print at a lower temperature. I went midprint from 192C to 185C to eliminate some warpage around sharp corner in that print. I do not do this often but have been able to successfully print as low as 182C with this extruder. I have always started to find discolored or burnt blobs of PLA extruding over 200C.

I had an issue similar to this a while back where the extruder motor wouldn't turn as fast as it was supposed to after a long while. I changed the motor and have printed fine for the last 8 months. I feel the motor shouldn't be the problem, it was warm to touch but no where near hot, and using an IR sensor on the HS of the extruder pololu I found 35C, with a cooling fan attached.

Do you look at the filament when it jams? Is the motor still turning? Can you hear skipping steps? Is the filament grinding?
To figure out where the problem is you're gonig to have to figure out where the jam specifically is.

---

Realizer- One who realizes dreams by making them a reality either by possibility or by completion. Also creating or renewing hopes of dreams.
"keep in mind, even the best printer can not print with the best filament if the user is the problem." -Ohmarinus

you don't mention the type of extruder - but - I'd check to see if your hobbed bolt or drive gear is worn or filled with plastic. also check your reference voltage on your driver, or swap it out. maybe the contacts have become dirty.

Possibly a broken wire to the extruder motor. The strands can be broken but it makes contact most of the time because the insulation holds the ends together.

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[www.hydraraptor.blogspot.com]

I had exactly the same issue.
Replaced the extruder motor (after many hours of systematically eliminating other things) and it now works perfectly.
I have since added a cooling fan & shroud to the motor.

I have the exact same problem with my Huxley. I did find out why it happens, you might check for the same: It seems that sometimes layers are uneven (bulging at some points) and the hotend scrapes through this causing a temporary block/jam of the movement.
I'm opening a new topic about this, because it might be totally unrelated to your problem, just with the same end result.

Thanks for all the repsosnes everyone, Sorry I was away for the weekend.

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MrDoctorDIV
Do you look at the filament when it jams? Is the motor still turning? Can you hear skipping steps? Is the filament grinding?
To figure out where the problem is you're gonig to have to figure out where the jam specifically is.

I have done many tests extruding the filament using prontrface: 100mm @ 50mm/min. When the filament starts skipping, yes the motor is still turning BUT it does not sound like it is skipping skips. I noticed while watching the extruder that after about 30-45 seconds the motor would momentarily slow down and then ramp back up again. The filament is not grinding, tangled or tensioned. The motor feels healthy for it locks hard when the leads are contacted or the coil is charged and rotates rather smooth when uncharged. I monitored the temperature of the pololu A4988 hs with an IR thermometer thinking it was getting to hot causing step skipping, however, after repositioning my cooling fan to maintain the sink at a temperature of 28-32C I still found the extruder motor to give the same results, skipping plastic.

Edited 1 time(s). Last edit at 06/22/2014 11:07PM by Prushead91.

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cat.farmer
you don't mention the type of extruder - but - I'd check to see if your hobbed bolt or drive gear is worn or filled with plastic. also check your reference voltage on your driver, or swap it out. maybe the contacts have become dirty.

I use an MKIV J-Head Extruder. my hobbed bolt is clear, O check it preiodically and I was at a refrence voltage of 0.5V, and using the basic Vref/0.4=Current I calculated about 1.25A. I am using PrimoPal http://www.primopal.com/web/Product4_GoodsID_22.html]PHB42S40-402[/url] stepper motors, rated for 1.7Amps. I even lowered the the Vref to 0.3V and still the motor gave the same effect I described in my previous comment

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PerformanceDefined
I had exactly the same issue.
Replaced the extruder motor (after many hours of systematically eliminating other things) and it now works perfectly.
I have since added a cooling fan & shroud to the motor.

I feel this may be the only solution to my problem. I had this same issue once before and changed the motor as well and found the problem to be solved. May I ask how long about did that motor last? Since you have added a means of cooling the motor do you think overheating or thermal failure of the servo is the cause of the malfunction? (and does it help keep the motor cooler to the touch?) and als