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Almost always missing layers / underextruding


Nicolinux

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Posted · Almost always missing layers / underextruding

Wow, thanks for the trouble you went through to test this. Very impressed.

And you are right, I think this could happen. I mocked-up this scenario from the image you linked:

teflon disaster

I imagine the grey filament gets caught in the space between the teflon exit (blue ring) and the nozzle entry (purple ring). It forms a bulge and makes it harder for the extruder to push through. And this is especially troublesome if retraction is involved.

To test this asumption I will print the retraction version and see if it fails earlier than the no-retraction version.

 

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    Posted · Almost always missing layers / underextruding

    Yeah. I wish I knew more about those simulations. Is there any way you/anyone could measure this area by taping a probe to it or something? If this is the problem it could explain why the filament snags in the head before hitting the inside of the tip, and why some filaments work better than others. If the differences in deformation temperature are right on the cusp of deformation some filament types my deform more readily into any interior surface deformations than other types. The XT should consistently work a little better for you if it can withstand higher temps in the hot-end, the manufacturers claim it can withstand temps up to 70C.

    Also, it's np; it wasn't much trouble to actually do anything. Typing everything up took the longest. I hope you figure out the reason for your troubles soon, the ending to this thread is killing me :smile:

    One more also, IF this is the problem it may be expressed at faster printing speeds if the extruder applies more column force to the filament via the bowden tube, forcing the filament to squeeze into surface deformations.

     

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    Posted · Almost always missing layers / underextruding

    Yeah. I wish I knew more about those simulations. Is there any way you/anyone could measure this area by taping a probe to it or something? If this is the problem it could explain why the filament snags in the head before hitting the inside of the tip, and why some filaments work better than others. If the differences in deformation temperature are right on the cusp of deformation some filament types my deform more readily into any interior surface deformations than other types. The XT should consistently work a little better for you if it can withstand higher temps in the hot-end, the manufacturers claim it can withstand temps up to 70C.

     

    I can't measure the temperature inside the teflon/nozzle connection. There is no way to reach in there even with the tiny temperature sensor I have here. I measured the temperature outside, around the height where the coupler and the nozzle should meet. It is about 110°. So PLA will definitelly expand if there is space left.

    temp

     

    Also, it's np; it wasn't much trouble to actually do anything. Typing everything up took the longest. I hope you figure out the reason for your troubles soon, the ending to this thread is killing me :smile:

     

    Haha, mee too :)

    I moved my UM2 to the living room because my Ultimaker happy corner is too small for tinkering. Good thing there are no ladies around right now, the WAF (woman acceptance factor) is way too low around here.

    By the way, printing the retraction variant didn't prove the theory. It even fared better than without retraction. Also the object on the left was at the front and features way more underextrusion than the on in the back. But I think that's just coincidence.

    retraction On

     

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    Posted · Almost always missing layers / underextruding

    Since the retraction length is so small, retraction may not exacerbate the problem. If it's that hot up there 110C, then the filament is definitely in a very pliable state and should yield to the retraction of the filament back into the head. It could be more of a function of material flow. I believe that because the machine is trying to pump out more material at the same temp and exit nozzle size the only thing that can change is the pressure inside the head. I may be wrong on this. This increase in pressure causes material to fill interior deformations which would otherwise be alright, but the material is almost in a snot like state creating too much drag at deformation interfaces and creating, I don't know exactly how to say it, some type of rubber band effect where the plastic filament doesn't yield fast enough to keep up with throughput anymore.

    If the head was hotter you should be able to print a little faster.

    Edit:

    Here is a "picture," I think this barley qualifies as a real picture. Now you know my horrible secret, the reason I use SW is because I have about zero art skills, this was done with my housemate's Wacom tablet.

    Anyway, what I'm trying to show here is that because the filament is under a lot of pressure and is also really long chains of molecule stuff that does not easily mix with itself at temps of 110 it can stick in the deformation and create drag on the remainder of the filament cross-section from there on down. Red indicating plastic molecules that move slower than the green plastic molecules, and yellow being somewhere in-between.

    1sYf0Co.png

    I should note that the filament is moving in the downward direction in this image.

    One more edit:

    Essentially the extrusion gets to the point where the motor has to not only push the filament through a 0.4 mm hole but also break the bonds between molecules in the filament and/or stretch them out a lot. And why I said if you print at a higher temp you should be able to print faster is because these bonds would be weaker at higher temps.

     

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    Posted · Almost always missing layers / underextruding

    Nicolinux - just posted something here. I suggest you increase your current a bit. It's not going to hurt anything. Add the following gcode towards the top of your gcode file:

    M907 E1350 ;increase extruder current from default of 1250ma to 1350ma

    More details:

    http://umforum.ultimaker.com/index.php?/topic/4222-pulling-force-of-um-extruder/?p=35887

     

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    Posted · Almost always missing layers / underextruding

    @AaronAlai: Hehe, call it a doodle and you might get away with it as "improvised art" :)

    @gr5: Thanks for the update, will test again.

     

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    Posted · Almost always missing layers / underextruding

    And another peculiar thing I noticed. Don't know how it could be related though. The teeth marks on the filament inside the bowden tube do not form a straight line but somehow rotate around the filament. I haven't noticed it before, maybe it is normal (and due to the filament curvature).

     

    Hm, for me this seems to be something mechanical rather than too less power of the extruder.

    In another thread someone noticed that the riffled wheel in the extruder got loose and therefore couldn't move the filament in the desired way.

    I think a misplaced riffled wheel can cause the teeth marks rotating around the filament.

    This is a picture I posted in the other thread to show how the riffled wheel should be adjusted:

    UM2 Feeder

    Maybe worth to check.

     

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    Posted · Almost always missing layers / underextruding

    Hey Siggi,

    Thanks for the idea. Already checked it. I put a mark on the stepper shaft and the knurled bolt mantle. The didn't move a notch since then, so I assume it doesen't move/slip.

    Um2 extruder teethmarks

     

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    Posted · Almost always missing layers / underextruding

    Is the Filament transported in the middle of the knurled bolt mantle?

    The 'teeth marks rotating around the filament' issue could be caused by a too outer placement of the mantle on the shaft.

     

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    Posted · Almost always missing layers / underextruding

    Hey you're right. The knurled bolt mantle is not centered on the filament. The filament sits on its edge. It could be that it doesn't always bite correctly.

    Ahh, I don't want to disassemble it again. The setscrew of the knurled bolt mantle is damaged. I might not be able to tighten it again properly. I think I'll order one on Ebay first.

    But thanks for the hint. This could be it.

     

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    Posted · Almost always missing layers / underextruding

    If you take a screw and not even the same diameter.

    You cut off the head and you make a notch.

     

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    Posted · Almost always missing layers / underextruding

    Tried it and failed. Even with a dremel - the outer surface wasn't clean enough.

     

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    Posted · Almost always missing layers / underextruding

    Wrote!

     

    So it will commancer a new piece :(

     

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    Posted · Almost always missing layers / underextruding

    Hi Stefan,

    Do you need a new set of screws?

    I can sent you a couple so you can replace the current one with a new one :)

     

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    Posted · Almost always missing layers / underextruding

    Wow, what a service. I have many of them, but they are too long. If it is not too much trouble to pop some in an envelope - then yes. Many thanks Sander!

     

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    Posted · Almost always missing layers / underextruding

    Ran the extrusion test again. This time I heard the skipping right from the start. And it started to underextruder at 3mm^3/s.

    I don't even..

    early fail

    I decided to stop tinkering and put the UM2 in its hapy corner until the parts arrive.

     

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    Posted · Almost always missing layers / underextruding

    Interesting results, I saw gr5's suggestion before I went to bed and hypothesized this would happen. I'm not saying it's definitely the teflon coupler, none of us seem to have enough information to make that assessment, and the hypothesis could just be a coincidence. I think that because you increased the current in the stepper motor, you also increased the amount of column force the motor can exert on the filament, thus forcing the filament into the interior deformations sooner into the print, causing under-extrusion. I like @ Sigi's comment above, if it is the teflon coupler then adding a rotational component to the assumed linearly displaced filament could exacerbate the under-extrusion issue as a function of deformations to the interior of the hot-end. Again, I'm very interested to see the consequences of replacing the teflon piece, if anything so I can start focusing on different hypotheses. Every time I think it could be this or that I reread part of the forum and haven't been able to come up with anything else that explains all the issues you've been having.

     

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    Posted · Almost always missing layers / underextruding

    Wait, forgot to say. I didn't increase the current. Just moved the knurled bolt mantle and printed the extrusion test.

    Makes it even weirder right? One possible explanation could be that the filament guide inside the extruder is bent or ground up for some reason. And now that the knurled bolt pushes the filament with full force, it does apply even more pressure on the (hopefully) broken teflon coupler.

     

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    Posted · Almost always missing layers / underextruding

    Blarp, well I still have the hypothesis nonetheless :smile:, I like your hypothesis as well, although only because it supports a broken teflon coupler :cool:. Are you planning on running the motor at higher current? I think it's worth a shot at least to see what kind of difference, if any, it makes.

     

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    Posted · Almost always missing layers / underextruding

    I do, but I'll wait for the new digital scale first. Yet since Amazon changed the delivery date to mid february I don't know if I can wait so long :)

     

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    Posted · Almost always missing layers / underextruding

    Double Blarp, well since you moved the knurled filament wheel to be more inline with the filament itself; could it stand to reason that you got lower load values earlier because of this phenomena? Do you think it would be worth redoing the tests you had already performed?

     

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    Posted · Almost always missing layers / underextruding

    I very much hope so!

    Still - I want to use a digital scale because I don't trust the cheap analog one. I'll see if I can borrow something from my friends.

     

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    Posted · Almost always missing layers / underextruding

    Hi guys,

    Got a delivery from Ultimaker today but I it was the wrong part :/

    Got this (1310 Hot End Isolator):

    No teflon inside

    But was expecting the teflon coupler for the UM2:

    teflon coupler 1

    @Sander: Could you take care of it? If possible please add the grub screw to the next delivery (if it is not already on the way). Also, where can I send the worng part back?

    Thanks.

    Stefan

     

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    Posted · Almost always missing layers / underextruding

     

    Geeks posted photos of a new design for the UM2 extruder - very interesting design. Simple. Maybe it's better.

    http://umforum.ultim.../3361-img-3791/

    He said he will post on youmagine shortly so it should appear here:

    https://www.youmagine.com/users/geeks

     

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    Posted · Almost always missing layers / underextruding

    Thanks. I will keep an eye on it _after_ I swap the teflon piece :)

     

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