Extruded filament is "pulsing" out of the nozzle

Hey reprap community,

i'm running my printer (prusa i3) for the last 3 month, but i still can't get it print correctly.

Some background:
I am printing with PLA at 195°C, heated bed at 60°C
Speed: 30mm/s perimeters and 50 mm/s infill at 20%
Using the E3D V6 hotend with 0,4mm nozzle.
Selfmade Direct Drive extruder, but no special Design.
Filament diameter: 1,75mm

There are many things that make me worry.

1) Holes are not round, although the axes are rectangular and the belts are tight. The steps per mm are ok.
In x and y-direction the diameter is nearly perfect with 20,04mm. In one diagonal direction it is 20,07mm and in the other 20,5mm?? Really strange.

2) The major problem right now: When extruding filament, it doesn't come out smoothly, but pulsing in a constant frequency.
I experimented with the temperature from 190° - 220°C at the nozzle: no difference.
I also tried Slic3r and Cura with similar settings, but the result is the same.
Also tried different kinds of filament.
At the beginning i thought, that the problem is the microstepping. Because of the less steps/mm compared to the geared extruder I used in the first month, the drive gear can't really turn smoothly.
So I thought this kind of "stop and go" of the drive gear results in pulsing filament. But the frequency doesn't match. I normaly use 1/8 microstep but I tried full-, half-, and 1/4-step because I expected a different behaviour, but it also makes no difference in pulsing frequency or anything else..

The reason for the pulsation has to be a lack of pressure inside the nozzle. But I don't know where it comes from.





I posted some pictures of my prints.
As you can see, the prints arent bad.
My main problem is that it is impossible to make parts for constructions with these uneven surfaces.

Does anyone have a possible solution for this problem?


Best regards

Puckit

It might be worth checking the hobbed bolt in your extruder (if there is one, otherwise the drive gear) for consistent diameter. Changes in the amount of grip it has on the filament may cause the pulsing you're describing. I would also look for any misalignment of the hobbed bolt and drive gears. Also check your filament diameter along a reasonable length to see if the diameter is consistent.

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[3DKarma.com] - suppliers of quality, affordable 3D printer kits and filament for the UK market.

Check your stepper driver, have you adjust the trimpod? Have you swap drivers? Sounds to me like your driver is at the barrier of been overpowered, does the stepper gets hot?

Thanks for the answers.

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3dkarma
It might be worth checking the hobbed bolt in your extruder (if there is one, otherwise the drive gear) for consistent diameter. Changes in the amount of grip it has on the filament may cause the pulsing you're describing. I would also look for any misalignment of the hobbed bolt and drive gears. Also check your filament diameter along a reasonable length to see if the diameter is consistent.

I will check the filament tomorrow. Doesn't the drive gear has to have an inconsistent diameter because it is hobbed...?

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ggherbaz
Check your stepper driver, have you adjust the trimpod? Have you swap drivers? Sounds to me like your driver is at the barrier of been overpowered, does the stepper gets hot?

Yes i did adjust them. I increased the current because the extruder was not able to handle 1/16 microsteps.. It couldn't feed the filament into the nozzle and lost steps.
I watched the temperature of the pololus while adjusting and they are cold during the print. I have a heatsink on them and a fan for cooling.
But you're right, the stepper of the extruder gets very hot.. I can still touch it, but doesn't feel comfortable.
Is there a certain temperature where the steppers loose torque?

I can't answer that, but constant high temperatures will deteriorate the enamel protection on the coils and once gone your stepper is dead. Try to bolt a 40x40x10 aluminum heatsink in the back of the stepper if you have space or use self-adhesive thermal tape and put the heatsink on top of the stepper and see if that helps.

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Puckit
Doesn't the drive gear has to have an inconsistent diameter because it is hobbed...?

The hobbed part has a smaller diameter than the rest of it, but I'm talking about checking whether or not the hobbed part is oval in cross-section or circular.

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[3DKarma.com] - suppliers of quality, affordable 3D printer kits and filament for the UK market.

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ggherbaz
I can't answer that, but constant high temperatures will deteriorate the enamel protection on the coils and once gone your stepper is dead. Try to bolt a 40x40x10 aluminum heatsink in the back of the stepper if you have space or use self-adhesive thermal tape and put the heatsink on top of the stepper and see if that helps.

I will try. I just have to find a heatsink form my old computers that fit.

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3dkarma
The hobbed part has a smaller diameter than the rest of it, but I'm talking about checking whether or not the hobbed part is oval in cross-section or circular.

The hobbed part is perfectly round.. the same diameter everywhere. It is also coaxial to the shaft of the stepper.

I made a video of a print, so that you can see the problem yourself.
I will upload it this weekend on youtube.

Here you can see the problem pretty well.

Printing Issues

It looks like your stepper motor is skipping steps. I can see that you've got a direct drive extruder - it may be that your stepper motor isn't strong enough to push the filament through. Can you post the model number of the motor? We should be able to look up how strong it is from that. You will possibly need to consider switching to a geared extruder or swapping out the motor for something stronger.

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[3DKarma.com] - suppliers of quality, affordable 3D printer kits and filament for the UK market.

If the extruder stepper is getting hot it can only mean one of 3 things which I would test in this order:

1) Too much current, turn down trim pot in very small steps and test. I had this issue when I built my first 3d printer. Using a multimeter or ohm meter with micro-clips makes the process very easy.

2) Faulty stepper driver. Try swapping the extruder stepper driver with one of the other sticks. It's not uncommon to receive faulty stepper drivers.

3) Faulty stepper motor (bad bearings, bad coils, partial internal short, etc). It's possible that your stepper was running too hot for an extended period and suffered damage as a result. A few of the cheper stepper motors I purchased a while back had dry bearings and were revived with a little lubrication.

I do 1/16 microstepping on my extruder without issue but I use a wade style geared extruder. Geared extruders are more energy efficient, they're easier on the motor and of course they provide much more torque. The only better option would be a geared stepper motor with direct drive.

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3dkarma
It looks like your stepper motor is skipping steps. I can see that you've got a direct drive extruder - it may be that your stepper motor isn't strong enough to push the filament through. Can you post the model number of the motor? We should be able to look up how strong it is from that. You will possibly need to consider switching to a geared extruder or swapping out the motor for something stronger.

Here is my model number: 47002350/0214RoHS NEMA17
There is the data sheet: Datasheed

I thought this is the "standard" stepper for extruders. Most of the makers use them also for the other axis. I used NEMA23 with 0.9Nm torque for x, y and z-axis.

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DeltaDroid
If the extruder stepper is getting hot it can only mean one of 3 things which I would test in this order:

1) Too much current, turn down trim pot in very small steps and test. I had this issue when I built my first 3d printer. Using a multimeter or ohm meter with micro-clips makes the process very easy.

2) Faulty stepper driver. Try swapping the extruder stepper driver with one of the other sticks. It's not uncommon to receive faulty stepper drivers.

3) Faulty stepper motor (bad bearings, bad coils, partial internal short, etc). It's possible that your stepper was running too hot for an extended period and suffered damage as a result. A few of the cheper stepper motors I purchased a while back had dry bearings and were revived with a little lubrication.

I do 1/16 microstepping on my extruder without issue but I use a wade style geared extruder. Geared extruders are more energy efficient, they're easier on the motor and of course they provide much more torque. The only better option would be a geared stepper motor with direct drive.

1) Well i did increase the current, but that was to see if that will solve the problem. I will check the current with my multimeter again and adjust the suggested 0.4A again.

2) Need to buy a new one first.. but i will test it.

3) I tried to get back to a geared extruder but i wasn't able to produce a circular gear. So there was an enormous difference in the extruded amount of filament during the print.. So i had to assemble the direct drive again until i solved my problem with the circles.... (my other big problem besides the extruder, as mentioned in my first post).

What voltage do you run your stepper drivers at? The datasheet specs that as a 12V motor (hence the low 0.4A current rating). The stepper drivers can't microstep accurately unless they get into the current limiting regime, which with that motor it won't unless you are using substantially more than 12V drive voltage.

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JamesK
What voltage do you run your stepper drivers at? The datasheet specs that as a 12V motor (hence the low 0.4A current rating). The stepper drivers can't microstep accurately unless they get into the current limiting regime, which with that motor it won't unless you are using substantially more than 12V drive voltage.

I am running the RAMPS with an ATX at 12V. So i think there can't be more than maybe 8V at the driver..
I didn't mention the Voltage when i bought the stepper.. well as mechanical engineer I'm more interested in the mechanics than the electrics ;D

I will measure the voltage that goes into the driver.

So usually the NEMA 17 steppers in combination with the A4988 stepper drivers are driven with about 8V?


Thanks for the answers.

In hindsight, I overstated my case. It might not get into current limiting, depending on the vref setting on the a4988. If the voltage measured at the test point (or on the wiper of the pot) is 0.22V then that would match the current rating of the motor (with the /70% adjustment), and the 12V almost certainly wouldn't be enough to drive it. But if you went for about 1/2 that, say 0.1v then you'd have a decent chance of staying current limited throughout the cycle. Of course, it might not produce enough torque then... It would be interesting to know what the Vref voltage currently is.

The resistance of the mosfets in the driver is given as less than 1/2 Ohm, so if the drivers are maxing out I'd expect you to see about 0.4V less than the stepper supply voltage across the motor coils.

If this has anything to do with your problem, then I'd guess the frequency of the pulses ought to be related to a full rotation of the stepper motor. I wonder if it's possible to make that connection or not? 4 pulses/rotation would be dead suspicious!

I have a similar problem only mine is limited to when I print PETG. When I print, some sides of a box are very smooth, but part of one of the sides is not smooth at all, it seems that when Z is incremented the plastic is not extruding smoothly when the new layer starts. The photo shows the defect. My setup prints smoothly for PLA, no problems. I am using Slic3r and Pronterface for the slicer and printer controller respectively. Speed does not seem to matter for PETG, I have varied speed and temperature but the defect is still there. My extruder seems to move freely. at least as far as I can tell. If I do random starts at each layer it helps a little, but I would rather be able to print smoothly. Any hints or suggestions?

SOLVED:

I bought a new Stepper for the extruder.
This one: New Stepper Motor

It runs smoothly, makes nearly no noise and doesn't heat up during the print.
I measured Vref at the Polulu with 0.45V so there should be a current of 1,125A (just in theory).

Thanks a lot for all ideas and help