Almost always missing layers / underextruding

[chrisp 10]

Braddock,

I thought I was in the clear after my changes, due to having the same exact problems with under extruding as you, but now they are back!

After about 8 good quality prints that I could walk away from, my nightmare is back.

We will definitely get to the bottom of this.

I started thinking that the STL files I downloaded were bad, so I sat down and starting drawing them from scratch and once I pressed print, they starting failing after the first 20-30 layers. The under extrusion was so bad it was printing in air with nothing coming out.

I will be taking apart the entire hot end tonight once again and posting pics and my findings.

 

[chrisp 10]

 

Ok here we go......

This clog was the worst by far. I started out by trying the change filament option via the controller. Nothing but grinding away the filament is what happened. I tried heating up the hot-end to 250 degrees Celsius and then tried removing the filament via the control panel and with a slight pressure of me pulling the filament with no success. I also tried move material but the filament was already grinded away inside the extruder. So what else is left? Taking apart the hot-end to see what is going on.

I usually start by taking out the 4 side fan screws and I tie up the fans and brackets to the axis rod so I get them out of the way and prevent the wire shielding to get heated up by the heating element.

Then I made sure to mark with a pen, the distance the Bowden tube is sitting inside the Teflon fitting. You can see the line marked with 3 dots which is not exactly against the Teflon, but close enough for reference.

I then loosened all 4 screws out of the aluminum bracket holding the nozzle in place and every other time so far the Bowden tube has come out without a fight. This time was different. I had to heat up the hot-end starting at 190 and gradually moving up to 250 degrees celcius until I could finally loosen the Bowden tube up enough to pull it out.

This is how the filament looked once I got it out.

Then I cut off the filament so I could get the Teflon fitting to go back on the Bowden tube to make sure it is sitting all the way down.

It's perfect no issues here.

Next I took the Teflon fitting and observed it very closely only to find that there's a lip inside the end that is seated into the metal hot-end nozzle adapter. I took my digital caliper and measure 3mm in diameter for the opening at the top of the Teflon fitting and 2.5mm for the diameter at the bottom of the Teflon fitting.

 

 

This I noticed once before but didn't think to measure it, but there is definitely some orange plastic stuck inside where the lip is and extremely hard to remove. I would like to razor knife the lip or drill it very carefully, but I need confirmation before doing so if it's not normal.

I then cleaned out the nozzle and saw light through it, which is hard to see in the pic.

 

Everything else looks great and I can't find anything wrong here besides the Teflon fitting.

 

 

[IRobertI 520]

Wait, so the "exit" of the teflon tube, the part nearest the hotend, is only 2.5mm in diameter? That's... not good. I'm surprised you're able to print at all to be honest. I know that there were a few cases on the original where people reported that the teflon had deformed slightly over time to cause it to be a bit too restrictive.

I guess it has to be a very short part of the piece that is actually at 2.5mm? If you push a piece of PLA through it, can you make it go through all the way (when cold)? The only way I can see how you have been able to print at all is if it's just a small lip at the end and that the end gets hot enough to heat up the PLA so that it can squeeze through (while at the same time deforming the teflon outwards perhaps?).

Regardless, unless my 1AM brain is completely incompetent that is definitely incorrect and I would use a 3mm drill bit to open it up.

 

[chrisp 10]

After carefully opening up the Teflon fitting to be the same size at both ends I put everything back together only to get this failed print! Same issue, nothing has changed.

I'm totally lost here and there's absolutely nothing I can adjust to make a difference during the print to correct the under extrusion.

And btw, I have another massive clog to deal with!

 

[Nicolinux 288]

I think it is time to contact support directly (Sander I guess). This issue is really annoying because (for me) it is totally random. I tried putting the filament spool on a lazy susan, printing at different temperatures, with/without combing, with the fan off or delayed and there is no pattern :(

There are prints with massive underextrusion, some with only a little bit of it and some prints with seemingly no underextrusion unless you look closer.

 

I am postponing all prints that are going to take several hours until I can fix this issue because I'd hate to waste so much filament just because some layers are missing.

I marked the bowden tube at the bottom, right benath the metal spring. While retracting I saw the mark jumping up and down so the bowden tube isn't seated firmly and moves in the direction of the retraction. I will print a new taller clip replacing the red on top of the black spacers on the printing head.

 

[chrisp 10]

After cooling down from another night of dissappointment, I decided to try something else. I adjusted the milled fitting that the teflon adapter sits into so that there is a 1.5mm space. It was sitting at exactly 1mm for the spacing before the adjustment.

I then leveled the buildplate because this adjustment changes the level that the nozzle sits at. I also took out the brim feature for the second try.

My print went from this:

To this:

Perfection once again.

 

I will be testing other colors and different length prints to make sure, because I have seen this before, then everything fails 5-8 prints later.

 

[Nicolinux 288]

@ChrispCreator: How did you adjust it?

I got impatient and tried a longer print. As expected underextrusion was there. Again not uniform, just in some areas.

Something odd happened. On the back, at the top, the underextruded area appears only on the left side, although a layer is circular and was printed a once. How can that happen?

 

Print settings:

 

• layer height: 0.2
  
• shell: 0.8
  
• bottom/top: 1.2
  
• fill: 2.5
  
• speed: 60
  
• temperature: 230
  

I had to lower the flow rate to 90% because it skipped like mad. Then midprint it was stable and at the end it started skipping again. This coincided with the height of the underextruded areas.

 

[chrisp 10]

Nicolinux,

Cool print btw!

You can adjust it by using one of the allen wrenches that came with your ultimaker and stick it into one of the milled holes and turn gently. If its stuck or too tight, then don't force it. mine turned really easy. (I forgot to mention that I turned it while in place, in case that wasn't clear) I didn't have to take anything apart.

The milled fitting has female threads on the bottom which screw into male threads on the nozzle. There is room to adjust the two because of this.

Hope this helps you!

 

[Nicolinux 288]

Oh wait, forgot to add proper captions :mrgreen:

Thanks for the hint and thank god I don't have to take anything apart...

 

[chrisp 10]

Haha......Nice!

Here's the second test. A 5 hour print 80% fill that has failed 5 times. This is a bracket for the X & Y axis and I need 4 total. I even redesigned this object from a failed print. So far so good.

 

On the left side are failed prints with 1/2 of them already in the garbage, but you can see that the failures are all at random times.

 

[gr5 2,170]

 

• layer height: 0.2

• speed: 60

• temperature: 230

 

With thick .2 layers you really need to print a bit slower. I think 50mm/sec is pushing it (60mm/sec is too fast I think) for a UM2.

Try 30 or 40mm/sec - this should reduce the underextrusion.

If you were doing .1mm layers then 60mm/sec is fine!

 

[gr5 2,170]

Basically if you hear the extruder clicking back/slipping/losing steps - rather than reduce flow, instead reduce feedrate.

 

[Nicolinux 288]

60mm/s is too fast at 0.2 layer height? Why? I am asking for 0.2 x 0.4 x 60 = 4.8mm^3 filament/s. Isn't an Ultimaker supposed to deliver at least around 10mm^3/s?

Ian was printing at 90mm/s with a 0.25 layer height without problems (http://umforum.ultimaker.com/index.php?/topic/467-post-your-latest-print/?p=32926).

 

[Nicolinux 288]

Basically if you hear the extruder clicking back/slipping/losing steps - rather than reduce flow, instead reduce feedrate.

 

Ok good to know. I thing I missed the menu entry where I can reduce feed rate. I only saw "material flow".

 

[braddock 1]

Guys, I ended up adding a second red horseshoe clip to try and keep the bowden tube in place and have been getting much better results.

I loosened off the 4 long screws holding the head together, pushed down the bowden tube to make sure it was properly nested, then, while still pushing down, tightened up the screws and added the second clip, which greatly reduces the amount of movement. I ran a succesful 15 hour print overnight with no under extrusion.

Annoyingly, it failed 15 mins from completion due to a layer misalignment in Y due to overheating... 30 degrees celsius in Sydney at 9:00am this morning!

The print, just before is screwed up!

 

 

[chrisp 10]

Braddock,

I fixed the Bowden issue by taking off the red clip, then pushing down the gray connector so that it is flush with the black plastic and the Bowden tube slides in and out easily. While holding the gray bushing in place push the Bowden tube all the way down then hold the tube in place while you slightly push the gray bushing up until it gets tight then put your red clip back on. Mines been holding in place for about 15 hours worth of printing without budging. the gray bushing sits a little higher than usual, but it actually works.

That's a crazy neat print you got there!

 

[braddock 1]

Thanks! how are you going with it now? reading above, that still hasn't solved all the issues? you've also lowered the milled plate?

What's this piece you've added here? did it help?

http://umforum.ultimaker.com/index.php?/gallery/image/2620-20140108-221039/

 

Braddock,

I fixed the Bowden issue by taking off the red clip, then pushing down the gray connector so that it is flush with the black plastic and the Bowden tube slides in and out easily. While holding the gray bushing in place push the Bowden tube all the way down then hold the tube in place while you slightly push the gray bushing up until it gets tight then put your red clip back on. Mines been holding in place for about 15 hours worth of printing without budging. the gray bushing sits a little higher than usual, but it actually works.

That's a crazy neat print you got there!

 

[braddock 1]

I was thinking something similar, but your version is more simple, here's a mix of the two. I dont use cad or solid works, I use Maya and Zbrush, neither of which are ideal for this sort of thing, so this is just rough, but you get the idea.

My thinking was, you'd put this on in the same fashion you did yours, then use a cable tie such as what I've added here, to keep it clamped to the bowden tube.

 

 

[illuminarti 18]

Yes, what is that?

Just tugging on my bowden tube, I have a mm or two of movement as noted before. Normally, the grey ring moves with the tube as I pull it. If I hold the grey ring down tight against the red clip (which is what it looks like that part in the photo is doing) then the tube still moves just as much, but slides inside the grey ring.

The only way to totally stop the Bowden moving at all is to move the grey ring up as far as it will go - which seems to be what braddock did with two clips, and Chrisp did by pulling the grey part up before adding the red clip.

These clips as used on the similar fittings on the cold end of the UM1 bowden are probably as good a way as any to hold it in place:

https://www.thingiverse.com/thing:46157

I'm not entirely clear what the relationship is between the teflon part and the metal fitting. When you adjusted it, Chrisp, did the metal move down, or the teflon part go up? i really need to take mine apart so I can understand how it's supposed to work...

 

Thanks! how are you going with it now? reading above, that still hasn't solved all the issues? you've also lowered the milled plate?

What's this piece you've added here? did it help?

http://umforum.ultimaker.com/index.php?/gallery/image/2620-20140108-221039/

 

[chrisp 10]

Don't look at that pic, it was an idea that failed. It made things worse.

Illuminarti,

When the milled fitting is turned to add more space between the Teflon fitting and itself, the nozzle moves up while pushing the Teflon fitting up, because it is sitting against the tip of the threads on the nozzle. I should have taken more pics, this just sounds confusing as hell, lol.

Basically, the Teflon fitting sits against the threads on the inside of the milled fitting and nozzle.

[braddock 1]

Illuminarti, when you change material, what does the end of your filament look like? are you getting the same ringed mushroom from filament being forced into a gap between the bowden tube and teflon fitting?

 

[illuminarti 18]

I haven't changed filament lately - but I'll make a point of checking next time :-)

 

[braddock 1]

Cool, if you're not getting that, I'd say miniscule play is ok... once it's enough for melted PLA to actually be forced into the gap during retrations, then it's an issue.

 

 

I haven't changed filament lately - but I'll make a point of checking next time :smile:

 

[braddock 1]

Anyone know if this would fit a UM2? It's exactly what I meant by "mechanical chuck"

 

 

[simmonsstummer 0]

Well, the movement of the bowden tube is a drammatical issue with um2. Can we print a red clip higher so the gray holder pressure is more firm?