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Looping Extrusion E3D V6 Kossel Mini

Posted by drentsoft 
Looping Extrusion E3D V6 Kossel Mini
April 13, 2016 07:33AM

I've got a Think3DPrint3D Kossel Mini with a 1.75mm bowden E3D v6 running reprapfirmware-1.09x-DC42 firmware (first printer) and I've started getting extrusion issues with PLA. When I extrude with the filament in the hot end, the motor stutters but does push filament through but the filament is coming out in a loop.

Originally the head had stopped extruding altogether so I tried dismantling the head as much as I could, shone a torch down the nozzle and the light came out clean the other end. After this I assumed the problem might be with the filament so I retracted and cut the filament where it had already gone through the extruder. When I extruded again it started extruding except for the issue described above where the filament comes out in a loop and the motor stutters. I cut both filament ends to points but the first end that wouldn't extrude never seemed to melt past a couple of mm.

The first picture is the result after 2 10mm feedrate, 10mm feed amount extrusions, the second is the comparison between a single 10mmx 10mm extrusion and the double extrusion. The last picture is just a close up of the nozzle because it doesn't look set up the same way I see most E3D v6's (it came pre-assembled with the kit). I'm printing around 200-205 though I'm not sure the thermistors are reading as accurately since I upgraded the firmware to 1.09x from 1.09k. In k the bed and heater seemed to be at most 0.5 degrees out from each other and seemed pretty close to the ambient temperature, since the upgrade they seem to be about 2 degrees apart and both seem to be several degrees above the actual ambient temperature (I have a thermometer in transit as I post this to check the difference). Changing the H values in config doesn't seem to help with this.

Any help would be appreciated. I'd just got my printer working properly with some help from a friend then this happened.
open | download - looped.jpg (416.5 KB)
open | download - singleDouble.jpg (565.5 KB)
open | download - headCloseUp.jpg (594.1 KB)
Re: Looping Extrusion E3D V6 Kossel Mini
April 13, 2016 08:23AM
The loops don't matter. Nice as it is when it extrudes cleanly in free air, it's common for it to loop like that. When you're extruding for real the plastic is pushed into a constrained space with plenty of surface area to adhere to.

The motor stuttering is bad however. You need to figure out why that is happening. Have you checked the Vref on the stepper driver for the extruder? Does the motor run hot, cold or warm? If the motor is cold then you have room to increase the Vref which will increase the force the motor can generate.
Re: Looping Extrusion E3D V6 Kossel Mini
April 13, 2016 08:33AM
I had similar problem with my extruder , turn out its was the thermistor that was not calibrate, like a 200C was giving me only175C and make my extruder grind,jam,skip step.

If you have a thermocoupler on a multimeter get the sensor into your nozzle and do some test to rule the thermistor calibration error out.

Mine was a clone E3D so the thermistor was kinda unknown, if your is a original with the original thermistor there probably some setting for RRP floating around to have it calibrate.

you need to find the value for B and H and L other user of that thermistor have ( M305 P1 T100000 B3950 R4700 H0 L0) The R will depend of your version of your duet board if you board have a sticker "4.7K" or not ( then its R1000)
Re: Looping Extrusion E3D V6 Kossel Mini
April 14, 2016 07:09PM
Thanks James,

I assumed the looping was an issue because it had always come out perfectly straight before (sometimes curling back up but never coming out in an actual loop) but thanks for the assurance. The motor is stone cold even after about 15 minutes of printing. Just to be clear, the stutters mainly happen when doing a 200-205 degree test extrusion at any feed rate/feed amount (mainly doing 10x10mm) it's less common when I'm printing though I think after about the 10-15 minute mark I do get the odd stutter. I'm wondering if this isn't as big an issue as it seemed. That said, during the test extrusion the PTFE tube between the motor and the hot end does seem to pull tight when it stutters. If you still think it's worth it I'll have a look at the Vref on the motor.

Thanks again
Re: Looping Extrusion E3D V6 Kossel Mini
April 14, 2016 07:18PM
Thanks GroupB,

Mine is an official E3D but since the firmware upgrade the temperatures do seem to have been a bit off. I found that when the firmware was upgraded the R was reset to 1000 instead of 4700, which lead to the values being wildly out. When I changed it back, checking all the values matched the previous firmware they seemed to get better but still seem a bit off. I'm still waiting on a thermometer that I can use to measure the temperature more accurately, unfortunately my multimeter doesn't have a thermocouple.
Re: Looping Extrusion E3D V6 Kossel Mini
April 14, 2016 07:48PM
I'd definitely dig in to any sign of the motor not turning smoothly. If the motor stalls then you won't get the expected amount of filament extruded and it will likely produce noticeably problems in the print. For the most part steppers tend to run at least warm (sweeping generalisation), so the chances are that the Vref is a bit on the low side and the motor isn't getting as much current as it could usefully handle. That said, a lot of experienced folk will recommend that the motor should stall in preference to chewing a semi-circle into the filament on the basis that you can recover from a stall and keep printing, but a divot in the filament usually spells the end of the print.
Re: Looping Extrusion E3D V6 Kossel Mini
April 15, 2016 12:49AM
So after you change back your R 4700 , do you still have problem ? Did you try to UP the temps see if its flow better and give less problem on the extruder motor?
Re: Looping Extrusion E3D V6 Kossel Mini
April 15, 2016 12:31PM
I did still have problems with R at 4700 but I think I've found the issue, the new firmware had the extruder motor at 500mA instead of the original 1000mA. I just changed it back and it seems like the extruder is working properly now.

Thanks for the help guys.
Re: Looping Extrusion E3D V6 Kossel Mini
April 15, 2016 05:29PM
I dont get it , you upgrade your firmware but why change your config.g ? Motor current and temp and such are set in config.g ... Updating firmware should not change your setting.

you dont really need to redo the config.g every firmware update...

I upgrade maybe 12 time already doing testing of firmware for the radds and I always keep my config.g
Re: Looping Extrusion E3D V6 Kossel Mini
April 15, 2016 06:48PM
I was just following the manufacturer's instructions for upgrading the firmware, I don't know why they said to do it that way but that's what they said so that's what I did. I assumed their firmware had the same settings as the stock DC42 firmware but apparently not. Next time I won't bother doing it that way and I'll keep the config file like you said.
Re: Looping Extrusion E3D V6 Kossel Mini
April 15, 2016 10:17PM
If the extrusion loops consistently to one direction, then it signals a partial jam. Try purging it at the highest safe temperature, or give the nozzle an acetone bath.

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