Almost always missing layers / underextruding

[mr.-waldorf 0]

Hey Nico, we are dead in the water again!!

It seems that you have the correct nozzle diameter and gr5 only can make some measurements on monday. This will not help your problem but could explain george's extrusion rates, if he has a bigger nozzle hole.

I saw that Ultimaker R/D team posted some comments on "Ultimaker2 Extuder System - Improvements and Ideas" topic so it seems that they also suspect of the extruder being the cause of some problems. Since they didn´t post anything here I can imagine that they don´t share with some of us the theory that a smaller nozzle hotzone is also causing the underextrusion at higher speeds.

I really hope that new teflon coupler can solve your underextrusion problem, but i really don't believe it

Meanwhile you realy have to change your UM2 rear, get a lazy susan or other way to feed the filament, because the stock way definitely cause underextrusion at higher speeds

 

[Nicolinux 288]

Hey Nico, we are dead in the water again!!

It seems that you have the correct nozzle diameter and gr5 only can make some measurements on monday. This will not help your problem but could explain george's extrusion rates, if he has a bigger nozzle hole.

 

 

Waiting... my least developed character trait

 

I saw that Ultimaker R/D team posted some comments on "Ultimaker2 Extuder System - Improvements and Ideas" topic so it seems that they also suspect of the extruder being the cause of some problems. Since they didn´t post anything here I can imagine that they don´t share with some of us the theory that a smaller nozzle hotzone is also causing the underextrusion at higher speeds.

I really hope that new teflon coupler can solve your underextrusion problem, but i really don't believe it

 

Personally, I don't believe that it is the extruder. This thing is strong enough. Something's wrong somwhere between bowden tube, teflon piece and nozzle. Or the board/stepper driver is broken and doesn't provide enough current at times. Looking at the last underextruded piece, the regular underextrusion pattern might indicate such a problem. Or maybe it is way less intricate and there is "only" some electrical interference due to a broken/damaged wire between the stepper and the board.

 

Meanwhile you realy have to change your UM2 rear, get a lazy susan or other way to feed the filament, because the stock way definitely cause underextrusion at higher speeds

 

Been there, done that.

I now use an exquisite swiss_design™ filament spool holder (courtesy of Robert - link). But I still experience underextrusion (another hint that it is not the extruder in my case).

 

[mr.-waldorf 0]

Waiting... my least developed character trait

 

:lol: :lol: :lol:

 

Personally, I don't believe that it is the extruder. This thing is strong enough.

 

I don't believe that is the extruder either, after some tweaks works fine.

 

. Or the board/stepper driver is broken and doesn't provide enough current at times. Looking at the last underextruded piece, the regular underextrusion pattern might indicate such a problem.

 

I was looking more carefull to the extrusion test photos, trying to understand your correlation. I can´t make that assumption/correlation just because of the regular pattern. However I agree with you, the source of the underextrusion problem could be there.

I noticed that between underextrusions you have a few layers well printed (no underextrusion) which sends a little bit my nozzle theory down the drain. If the nozzle didn't have enough time to heat the filament at higher speeds It shouldn't have good extrusion between underextrusions.

 

Or maybe it is way less intricate and there is "only" some electrical interference due to a broken/damaged wire between the stepper and the board.

 

Don't think so! This is not an isolate problem on your printer. Did you noticed the views/replays of this thread? This is a widespread problem...

 

Been there, done that.

I now use an exquisite swiss_design™ filament spool holder (courtesy of Robert - link). But I still experience underextrusion (another hint that it is not the extruder in my case).

 

Wow RESPECT Robert!! Awesome design and it works great. I will print one Thanks

 

[mr.-waldorf 0]

HA HA! Caught on camera on Valentine's day...

The underextrusion occurs at:

3.23s

4.03s

4.30

4.50

5.23

Illuminarti's UM2 - Extrusion Test 3-10mm3

UM Gold PLA

230ºC

Test failed at 4mm3/s

The stepper motor is jumping backwards it seems a defective or underpowered stepper motor.

 

think I have to further investigate, but not today. Happy valentine's day!

 

[geeks 1]

HA HA! Caught on camera on Valentine's day...

The underextrusion occurs at:

3.23s

4.03s

4.30

4.50

5.23

Illuminarti's UM2 - Extrusion Test 3-10mm3

UM Gold PLA

230ºC

Test failed at 4mm3/s

The stepper motor is jumping backwards it seems a defective or underpowered stepper motor.

 

think I have to further investigate, but not today. Happy valentine's day!

 

I noticed the same thing when the nozzle cools.

 

Look at the electrical level:

The temperature drops at the level of nozzle. The engine grows and requires more power. The nozzle has not resumed an adequate temperature and engine as the current request.

 

The power supply is strong enough?

 

[shurik 87]

The stepper motor is jumping backwards

 

A-ha! That's exactly what I had while trying to print some buildings! Solved the problem by reducing the flow to 80%.

Not sure what it means, probably some inperfect overflow handling by the machine itself.

 

[aaronalai 2]

HA HA! Caught on camera on Valentine's day...

The stepper motor is jumping backwards it seems a defective or underpowered stepper motor.

 

think I have to further investigate, but not today. Happy valentine's day!

 

Thanks for the video upload Mr. Waldorf, I have a rather specific question for you or anyone that has uploaded a similar video and I hope it comes across clear enough.

Alright, I've been watching a lot of videos where these extrusion motors "JUMP" backwards. It was my belief that the motor current circuitry was designed in such a way that if the motor did not have enough current to facilitate the displacement of the filament, the motor would stall but keep it's approximate location with respect to the rotational motion it provides, and to not jump backwards loosing stored pressure in the nozzle causing under-extrusion.

These jumps backwards indicate to me that there is the storage of potential energy inline with the filament somewhere, or potentially the bowden tube; upon the motor stalling the filament pushes back against the knurled wheel spinning it in reverse. I think this is quite clear; the question is though, where the potential energy is stored within the filament or filament encasement. I think it can be stored in several locations, but currently I believe it is the result of a deformation in the teflon coupler; I'm very willing to concede that there are other locations of potential energy storage though.

So the question I have for you or others is this, do you observe under-extrusion before or after the knurled wheel spins in reverse? If under-extrusion happens before the motor spins backwards, I would be more incline to believe it is a problem with the nozzle head, and potentially the teflon coupler. Imagine the extruder motor trying to push the filament, but the filament not being able to flow out of the nozzle creating more back pressure (potential energy) than the system was designed to handle, and bam the motor spins in reverse. If under-extrusion happens after the motor spins backwards, I would be more incline to believe it is a problem with the circuitry that controls the motor. Imagine the motor trying to keep an almost static load applied to the filament while pressure is being released from the nozzle end, but due to an electrical problem the motor looses all capacity to hold a static load on the filament and spins in reverse as a function of the release of stored potential energy somewhere in the filament or filament encasement system.

I don't think answering the question will yield a definitive conclusion, but I believe it will help the UM community home in on the problem because of the more detailed cause and effect relationships between the nozzle dispensing material and the feeder feeding material. This relationship is unclear, to me at least. I also understand that my question may be difficult to answer, you can't watch both the nozzle and the extruder motor at the same time; but I'm hoping that the sound the extruder motor makes is clear enough to note the exact time it occurs with respect to the nozzle depositing material.

Edits; grammar and clarity.

 

[yellowshark 153]

Hi Mr Waldorf, I do not have any definitive answers as I have not specifically done any testing between the same/similar colours between manufacturers. What I will say is

 

1. 
   I have not detected any major differences between Faberdashery and Colourfabb filaments in terms of temperature needed.
    
   At one point I did think that Colourfabb ran cooler by 5 degrees but that was before I determined the impact of different colours, so I am not sure now. Someone else posted a couple of months ago that they found Colourfabb to run hotter.
    
   

 

I will try to do some “comparative” testing in the next couple of weeks.

 

 

1. 
   Similar colours from the same manufacturer can show significant differences
    
   

 

Arctic white from Faberdashery runs

200 microns 30 m/s at 210

300 microns 60 m/s at 220

Pearly white from Faberdashery

300 microns 40 m/s 230

300 microns 60 m/s 250

 

For me Pearly white is a strange one, as other Faberdashery filaments I have used I have run at the Arctic white temps or very close.

 

[Nicolinux 288]

Thanks for the video upload Mr. Waldorf, I have a rather specific question for you or anyone that has uploaded a similar video and I hope it comes across clear enough.

Alright, I've been watching a lot of videos where these extrusion motors "JUMP" backwards. It was my belief that the motor current circuitry was designed in such a way that if the motor did not have enough current to facilitate the displacement of the filament, the motor would stall but keep it's approximate location with respect to the rotational motion it provides, and to not jump backwards loosing stored pressure in the nozzle causing under-extrusion.

These jumps backwards indicate to me that there is the storage of potential energy inline with the filament somewhere, or potentially the bowden tube; upon the motor stalling the filament pushes back against the knurled wheel spinning it in reverse. I think this is quite clear; the question is though, where the potential energy is stored within the filament or filament encasement. I think it can be stored in several locations, but currently I believe it is the result of a deformation in the teflon coupler; I'm very willing to concede that there are other locations of potential energy storage though.

So the question I have for you or others is this, do you observe under-extrusion before or after the knurled wheel spins in reverse? If under-extrusion happens before the motor spins backwards, I would be more incline to believe it is a problem with the nozzle head, and potentially the teflon coupler. Imagine the extruder motor trying to push the filament, but the filament not being able to flow out of the nozzle creating more back pressure (potential energy) than the system was designed to handle, and bam the motor spins in reverse. If under-extrusion happens after the motor spins backwards, I would be more incline to believe it is a problem with the circuitry that controls the motor. Imagine the motor trying to keep an almost static load applied to the filament while pressure is being released from the nozzle end, but due to an electrical problem the motor looses all capacity to hold a static load on the filament and spins in reverse as a function of the release of stored potential energy somewhere in the filament or filament encasement system.

I don't think answering the question will yield a definitive conclusion, but I believe it will help the UM community home in on the problem because of the more detailed cause and effect relationships between the nozzle dispensing material and the feeder feeding material. This relationship is unclear, to me at least. I also understand that my question may be difficult to answer, you can't watch both the nozzle and the extruder motor at the same time; but I'm hoping that the sound the extruder motor makes is clear enough to note the exact time it occurs with respect to the nozzle depositing material.

Edits; grammar and clarity.

 

Hey Aaron,

my obeservation is that underextrusion occurs slightly after the extruder jumps back.

Another seemingly related factoid I noticed while performing the extruder pulling force test (link) - the sound from the stepper changes its pitch when it is maxed out (e.g. before it slips back due to the weight). While printing I have never noticed this change in pitch (but this on the other hand might also be due to overall increased noise level).

 

[aaronalai 2]

Hmm, interesting. I'm not abandoning the teflon coupler explanation just yet; even with your reported observations the sequence of events may be too close to identify causality. There is a chance that potential energy stored in the head (as a function of a teflon deformation) is reaching a critical point, but the stepper yields and spins in reverse before under-extrusion can be observed at the head. But your observation has lead me to think about the problem a bit differently nonetheless. Let's see if we can rule out the stepper controller circuitry.

I'm looking at the board schematics found here: https://github.com/U...aker/Ultimaker2

mnis suggested through our communications that he thought the chips were too small to not be actively cooled, I've also seen others question if not having an active cooling system on the board can cause any problems. So I thought I would look at the schematics to find the chip type (I agree they do look too small to not be actively cooled); but without a data sheet I can't do any calculations that could tell me anything conclusive.

The pdf of the board does not specify the chip model, if someone could post a chip model number, I'll see if I can find the datasheet and do some calculations using the thermal resistance information.

After doing some calculations with the default current allowance of 1.25 amps Ultimaker sets in the firmware, and some assumed thermal resistance and RDS(on) values; I don't think those chips can overheat very easily. Even if the thing had a Junction-to-ambient temperature of something like 80 C/W (just making up numbers here, a pretty large value nonetheless), an RDS(on) value of 0.04 ohms, and it was suspended in free air, the thing would probably rise only 5C in temperature. Without anything more to go on then estimations, I can't follow this line of rational to it's conclusion though.

Edit:

This is an image of the board:

If someone could tell me what the chip labeled U12 under the E1 interface is, I'll do my best to do some worse case scenario thermal calculations.

 

[mr.-waldorf 0]

Hey Aaron,

my obeservation is that underextrusion occurs slightly after the extruder jumps back.

 

Same here. Few milliseconds after the extruder Jumps backwards

 

[mr.-waldorf 0]

Right before the stepper motor jumps backwards it seems to be a slight increase in nozzle pressure. That´s the reason why if we deacrease the flow we can avoid a litle bit the underextrusion. But doesn´t mean that the filament is not being able to flow out of the nozzle creating more back pressure. To me it seems that there is more back pressure but only due to higher flow rates and the stepper motor is underpowered.

I have the feeling that the problem isn´t the nozzle head but the stepper motor or motor driver/Board. Meanhile I have to prove that! :mrgreen:

 

[mr.-waldorf 0]

Also noticed that the 'backward jumps' are different in length. it's not a controlled movement

Not saying that is this the problem but as the behavior of an electric motor with defective magnets, it slips under stress

 

[aaronalai 2]

Yeah, I did notice the jumps were not all of the same rotational distance; I understood this to help prove the teflon hypothesis though; as putty like filament gets crammed into any interior deformations at higher pressures/flow rates (the temperature and nozzle diameter cannot change so the only thing that can change is the pressure inside the nozzle) I wouldn't expect to see the extrusion motor spin backwards until the material stretched to a certain extent which would have some variability to it because of the constant release and build up of pressure from the extrusion motor.

I can also see it being a function of a defective stepper motor as well. I think until I get a datasheet for the controller chip of the feeder stepper, I can conclude that the circuitry is pretty sound; leaving the motor as the next suspect.

I wouldn't expect the motor to be allowed to rotate that far backwards; the folks at Ultimaker would have to know that it would cause an extreme release of pressure in the nozzle causing under extrusion while the head built up pressure again. I believe it was their intent to have the motor stall but still apply a load to the filament until the motor could spin again. I see what you are saying, if the motor itself if faulty then it could explain why the backwards spin is so great resulting in under-extrusion. It's like once the stored potential energy (from wherever it is stored) is released the motor just gives up and takes too long to move the filament again.

It's just a thought, and admittedly one that just came to me so I haven't had much time to really think it though. But when the filament is at room temperature, I think it would be rational to conclude that it wouldn't have much of a capacity to build up potential energy, it's too stiff. If you could hold a very short segment of the filament at the very exit of the extruder (take off the bowden tube and hold the filament in your hand very tightly, I really don't know how feasible this is) you could see if the motor just sits idle trying to move the filament (I wouldn't expect any springy action to push the knurled wheel in reverse), or if it just gives up when it reaches it's current limit and you can move the move the filament freely for an instant. If the ladder happens I would guess the motor is missing steps (something I don't think it should do), potentially being a way to test your hypothesis. Essentially this would tell you if the motor was always applying a load to the filament but the filament pushes back too much, or if the motor simply looses power momentarily.

 

[mr.-waldorf 0]

Hi Aaron,

I made the extrusion test with the filament out of the bowden tube just running free in my hand and the motor didn´t jump backwards

Made a second extrusion test and I tried to push the filament with my hand and then with a pliers and the motor didn´t step backwards. I was able to stop the filament and the motor just chewed the filament.

Not the results that I was expecting... and I am not sure if this test results can mislead us

I will repeat this test more times to see if there is consistency in the results

 

[Anders Olsson 136]

I had severe under-extrusion on long PLA prints on my UM2 upon delivery.

After reading through the 24 pages quickly I did not see anyone mentioning the nut that sits behind the stepper motor for the feeding mechanism (or did I miss that post?):

On my UM2, the hole in the chassis plate was not deep enough to fit the nut.

This made the stepper motor sit with a slight angle.

The resulting angle on the motor shaft moved the knurled gear away from the ball bearing.

This resulted in:

1. Less pressure on the filament, making friction in the spool unwinding mechanism more of an issue.

2. The filament not centered, making it grind towards surfaces inside the housing.

3. The ball bearing positioned too far out, making it grind on the plastic housing.

4. The mechanism more sensitive to filament thickness, since there is less play in the bearing spring available to compensate for thinner filament.

5. The chance of the filament getting stuck when slightly grinded much higher.

The solution in my case was to simply remove the screw and nut.

Since then I have not had any under extrusion issues. Although I have mostly been printing ABS since the repair and under extrusion happened with PLA, so I should try a long print with PLA some day to confirm that it works with PLA too.

I also experienced that the noise of the feeding motor decreased significantly after removing the nut.

Here is a video of my feeder mechanism, loading ABS, after the nut was removed:

 

As you can see, the ball bearing is pushed in significantly when the filament is inserted. This was not the case before I removed the nut, the bearing was barely pushed in at all then.

Regarding the filament spool holder, there was an extra "knob" delivered with my UM2. The manual said nothing about it, but using it as a guide for the filament improved feeding (before i found the nut behind the stepper motor):

(the knob in the lower left corner)

 

[IRobertI 520]

The springiness is stored in the PLA and bowden. The filament acts as a spring inside of it. As the extruder pushes, the PLA will in turn bend and twist and push itself into the walls of the bowden tube. The bowden has a slightly larger ID than the OD of the filament so the filament can bend sideways a little bit. I'm trying to come up with an analogy but my 3:30AM brain is telling me to shut up and go to bed...

As for the motor allowing the filament to slip through. Imagine yourself pushing with all your might against something until your footing gives way, can you immediately regain your footing and keep pushing? Nope, you slide a bit until friction becomes your friend again. Same thing with the motor. You've got filament shooting out at velocity the same way your legs will kick out because your muscles have built up pressure that gets released. Well, ok, not the _same_ way, it's a silly 3AM-brain-tired-wants-sleep-why-am-I-still-up-analogy, but you get what I mean.

I have no idea if any of that made any sense. Bed.now.go.

 

[mr.-waldorf 0]

Hi Anders Thanks.

 

On my UM2, the hole in the chassis plate was not deep enough to fit the nut.

This made the stepper motor sit with a slight angle.

The resulting angle on the motor shaft moved the knurled gear away from the ball bearing.

 

Not the case here.

 

Regarding the filament spool holder, there was an extra "knob" delivered with my UM2. The manual said nothing about it, but using it as a guide for the filament improved feeding (before i found the nut behind the stepper motor):

 

(the knob in the lower left corner)

 

the filament guide even horsted the underextrusion

Print illuminarti´s extrusion test at 230ºC. Maybe you have underextrusion but you didn´t notice because you are printing with lower extrusion rates if not it's always interesting to know that there is UM2 that can achieve higher extrusion rates

 

[mr.-waldorf 0]

Hi Robert,

Do you thing that it's the springiness stored in the PLA and bowden that causes the motor steps backards?

I will print the some underextrusion test with lower flow % and play a bit with that.

My teflon coupler and nozzle seems to be ok, so maybe its just a question to find a better flow% than the default 100%

 

[mr.-waldorf 0]

Hi Nico

Before changing the teflon coupler try printing the extrusion test with 90% flow

With 100% flow I have underextrusion at 4 - 5mm3/s and with 90% flow I Made 10mm3/s without underextrusion.

It's a way to overcame the motor jumps backwards and of course the underextrusion.

Should be very interesting if you have the same results as I and after that you could change the teflon coupler and test the extrusion rate again with 100% flow

 

[aaronalai 2]

Definitely interested to see the results of such a test, a 10% reduction in the flow rate from other peoples print seems reasonable; the difference could easily be from the summation of assembly/parts tolerances. I hope the problem is as simple as this :mrgreen:

 

[Nicolinux 288]

I don't think so:

It's hard to see, but underextrusion started at 6mm^3s. Printed at 230° and 90% flow.

 

[aaronalai 2]

Shoot! It's hard to tell who has what type of exact problem; perhaps most of the under-extrusion problems are a function of settings but you have a somewhat different problem. When are you suppose to get that teflon coupler?

 

[Nicolinux 288]

Don't know. Asked Sander about a week ago and he said the teflon coupler is on its way. I'll ask again tomorrow.

 

[Anders Olsson 136]

I have done some tests now.

The ABS came out perfect on first try.

When trying PLA, I suddenly realized why I never switched back to printing things in PLA after I tried ABS..

PLA certainly has a more sticky surface. I added an extra pulley before my extruder to guide the filament into the feeder, just to avoid potential problems with the spool unwinding:

This thing has not been tested for normal printing though. I don't know how it will handle the filament retracting.

With ABS I never had problems with this part of the printer.

The version in ABS came out perfectly fine on standard settings (260C) as you can see here:

 

When running the PLA at 210C the feeder started skipping and underextruding at 6mm3/s.

I quickly increased the temperature to 230C, which I read people here had been using for printing this thing in PLA.

It worked until 10mm3/s, when it underextruded again and I increased to 240C.

 

I then tried another time at 240C, but the filament unwinding jammed a bit in the end of the print.

 

Next try at 240C worked well except when going from 9-10, where I had some underextrusion.

 

I then tried at 250C, which seemed a bit better, but still there was some slight underextrusion the first layers at 10mm3/s.

 

My conclusion is that maybe we should have a look at the extrusion properties of PLA, trying to determine if it is really suitable for flows rates this high.

Many plastics has kind of a non linear viscosity. (I am not a chemist, there are probably better words for this).

This property of the plastic will make the extrusion force increase more in an exponential way than in a linear way, when pushing the plastic through a small nozzle at an increasing flow.

 

This is my current thought about why the force needed to extrude PLA seems to increase rapidly as flow is increased.

As I said, ABS came out perfectly fine on standard settings, but ABS is a different plastic too which most likely has different extrusion flow properties.

 

Particularly interesting is how underextrusion occurred for both 240C and 250C the first few turns when going from 9-10mm3/s.

I don't see exactly how this would happened if it was a mechanical problem.

Looks more to me like there is something going on with the melting and the viscosity of PLA at these flow rates.

 

So maybe in the end you are just trying to defeat the extrusion-properties of PLA when running it at this high flow?

 

For me this is a bit of a non problem in the end, since I am not going to print PLA at this rates anytime soon anyway.

 

..time to get back to my experimental HDPE extruder..