Almost always missing layers / underextruding

[woofy 12]

Nicolinux,

I'm using the Faberdashery spool holder I put on Youmagine yesterday.

https://www.youmagine.com/designs/spool-holder-for-loose-filament

That's Faberdashery Arctic White wound on there at the moment.

 

[aaronalai 2]

Hey WoofysPlace, can you post an image of your damaged teflon coupler?

Very glad to hear about your success!!!!

 

[pikey 0]

Where did it crack?

This is the ring that went around the bearing, It cracked in half. I prefer the bearing against filament directly personally. Getting the spacer out of the inside of the bearing was a huge hassle too.

 

[gr5 2,172]

Perfect 10/10

Wow!! :eek: Wow :-P . This is important.

So...

Please go back and put one of the old parts back on. Whichever is easier. The bowden maybe? Not this minute but when you get a chance. Here are my odds:

60% problem was with nozzle

40% problem was with bowden

 

[IRobertI 520]

This is the ring that went around the bearing, It cracked in half. I prefer the bearing against filament directly personally. Getting the spacer out of the inside of the bearing was a huge hassle too.

Ok, thanks. The guide ring can probably be "optimized out" of the design as it's a remnant from my first attempt where it was needed to keep the filament in place. The spacer slides in and out of my bearing without any effort.

And I guess I could fatten up the area around the nut.

But meh, interest is too low to bother. You're the only one who has tried it besides me, which I appreciate.

 

[pikey 0]

No problem, I love these designs. The yoke on your feeder was awesome, I used it all the time to give the printer a helping hand when testing different spring tensions and had to bypass a chewed up portion of filament. Interest is high from me!

 

[takei-naodar 0]

Just wondering does anybody bother doing the extrusion test with retraction?

I just printed that one with 140% Speed.

 

 

[gr5 2,172]

I just printed that one with 140% Speed.

 

show off!

 

[takei-naodar 0]

You just envy me. Admit it

 

[Nicolinux 288]

Hey guys,

I have found/documented something else that hast to do with pressure. Sometimes when I start a new print, pressure seems to build up and a big blob of plastic is extruded. After that, the print pretty much fails because there isn't enough filament comming out (even with two or three outer loops of skirt).

This usually happens when tha printer is "cold". So my assumption is that the deformation inside the teflon coupler is very much a concern when it comes to underextrusion because it can manifest in such a extreme way at the begining of a print.

Check out this video (sorry for the focus fail at the begining):

 

[Nicolinux 288]

Hey Markus, thanks for the ideas. I can move material just fine (and when I do that before a print, this problem never occurs). The bowden is clear and well seated. This problem appears sometimes between perfect prints.

 

[mnis 11]

Sorry, maybe I've just edited while you've already answered. Please read the previous again.

I've just viewed your video again enlarged. The thing with the Blob I do not understand so completely, that could be a sudden tension degradation. Does the rear fan correct? I also believe that the nozzle too far could be away from the glass surface.

Markus

[Nicolinux 288]

Hey Markus, as I said. This happens between perfect prints. So other prints are really fine and I don't change anything between them. The 3rd. fan works correctly (well it is broken because it is loud as hell, but at leas I know it is spinning fast).

The blob forms right when the first extrusion occurs. After that the skirt is printed but as you can seen in the video, there isn't a continuous filament strand. Eventually (if I let the print continue) the plastic flow stablizes but by then the first layer is half through (and not smooth as it should be).

 

[mnis 11]

You could be print more Skirt-lines around your object, and the starting distance increase, maybe it stabilizes then still in time.

But also some loose connection could temporarily cause problems.

Oh, you could try by means of the adjusting screw of the feeder, to increase the pressure of the filament against the knurled wheel. It is not recommended in general, but trying does not hurt.

good luck

Markus

[geeks 1]

I have the same problem! :twisted:

 

This effect occurs because the force applied at the beginning of the impresion, when touching the plate is too large.

 

Stage of start print:

- I think that if the head is close to the plate.

- The head is hot. 

- It should be a step in the extruder. 

- Then add 2ms (time to warm up the nozzle) 

- Start the displacement of the filament with the displacement x and y. 

So I think a fix on Marlin to avoid this.

 

There is no cap, but a little too much pressure while the head is not ready to print.

 

To work around this problem. Go to "move material" menu, leave up to 210 ° C and then manually extrude a bit of material. Exit this menu and start a print. It will no longer appear this defect.

 

[mnis 11]

Yes exactly that I have Nico suggested in my first reply:

"Have you ever tried using the "Move material" function a few strands manually extrude? The manual extrusion should at least give a nearly continuous filament strand."

I do not know if he has already tried it.

Markus

[illuminarti 18]

On the video there seems to be a clunk sound right at the point of blobbing - what is that? It doesn't seem pressure related or bed/head closeness - it's more like an un-needed de-retract that makes the feeder skip back, so there's subsequent under-extrusion. I'd say it's a slicing or firmware bug, rather than something mechanical. It just looks like it tries to massively over-extrude in place, right at the start of the print.

[Nicolinux 288]

@mnis: I tried this solution. If I move material and then start a print, the blob won't appear.

@illuminarti: Exactly, it tries to overextrude too much at the begining. Don't know why. It is not related to a single model.

 

[illuminarti 18]

Does it always do it with the same gcode? Is there anything odd in the gcode? Does it only do it after you've already completed a print (without power cycling in between)?

[pikey 0]

I'm having the exact same problem. I think that the nozzle stays too hot for too long (or while heating up). I think there is still pressure in the bowden tube.

 

[Nicolinux 288]

Does it always do it with the same gcode? Is there anything odd in the gcode? Does it only do it after you've already completed a print (without power cycling in between)?

 

I can't say for sure, but I think it happens randomly and it is not tied to a specific model. And since I am shutting off the printer while it cools down (3rd fan broken and loud), I think I power cycle before most prints.

 

[illuminarti 18]

Next time it happens, send me the gcode to take a look at and/or try out.

[gr5 2,172]

I think this is caused by air in the nozzle or maybe an air bubble sealed in solid PLA retracted up into the head away from the heat a bit.

When a nozzle is hot but not extruding, filament drips out and eventually presumably air gets in. Or maybe when you retract at the end of the previous - maybe that is when the air gets in.

When you heat the air, it expands and pushes some liquid PLA out.

 

I can move material just fine (and when I do that before a print, this problem never occurs). T

 

That's my solution also. I'll even do "move material" cold and move it until I see the PLA touching the top of the bowden.

 

[Nicolinux 288]

@gr5: Meh... I don't want to always have to move material before a print...

@illuminarti: It just happened again. The printer was on and waited after the print was done. I removed the object from the glass plate and started another print. Then the blob occured. I have attached the "offending" gcode file (the stretchy bracelet - link).

I don't think it is related to an object because I had it with all sorts of prints. It is either what George said or maybe a firmware bug. Maybe the extruder extrudes too fast at the beginning. These kind of bugs are not impossible. I remember another bug where the head traveled too far when one selected something in the ulticontroller while the head was homing home.

 

[illuminarti 18]

Gcode looks ok... did the printer do it's pre-extrusion thing as it moved over towards the bed to start the print? Any reason to think that was getting hung up, or building pressure? In your video it looked like that happened ok, and then it did extra extrusion right after?

What firmware version are you running?