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Nicolinux

Inconsistent z-wobble

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Hi,

I am still fighting with z-wobble because my z-stage isn't stable (see http://umforum.ultimaker.com/index.php?/topic/2716-cannot-lower-bed-to-reach-endstop/ if you are interested).

However, I noticed that some models feature some inconsistent or invariable horizontal lines. I thought that when z-wobble is present, those lines would be always there.

This owl for example features some prominent horinontal lines around the waist, but not later on.

Owl zoom

Owl

Then I have models with zero wobble like this:

No Wobble 2

No wobble

And models where wobble is all over the place but still not consistently aranged:

Mini Zombie Hunter

Screwless Gear Cube

Toy Car right

Toy Car left

I also noticed that sometimes the surface is very regular where one layer is shifted backwards and the next layer positioned normally. This repeats itself for the entire model:

Weird uniform wobble

 

 

Sorry for so many pictures...

Any idea what it could be? Maybe the z-stage is very unstable and while the machine vibrates it also moves up and down.

 

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Then I have models with zero wobble like this:

 

Interesting!!!

This makes me think there is nothing wrong with your z stage. If that green part can look so perfect.

What was different about the green part? Did you print it much slower so that the machine shook less? Or slower could have caused more even extruding? Maybe the filament diameter for blue and white is too large and gets "stuck" in the tube? Maybe something wrong with the slicer? Maybe something to do with infill?

 

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Good question. I printed the green iPhone stand with the following settings:

 

  • layer height: 0.2
  • shells: 0.8
  • bottom / top: 0.6
  • infill: 20
  • speed: 75
  • temperature: 225
  • filament diameter 2.85

 

At least for the blue filament I have the same diameter. The white one is larger - 2.94. The other stuff I printed mostly with 0 infill. That might be it. But why on earth would zero infill make it worse? Except there are some complicated corner cases where, without infill the filament contracts/expands differently when cooling thus amplyfing z-wobble problems. Weird...

 

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Sorry, I can't remember. I do write everything else down, but I always forget to record the printing time. And since my OctoPrint installation doesn't work right now, I don't have any other records than the UltiController (until I start the next print that is...).

The print took several hours - that's for sure. Here are the printing parameters:

 

  • layer height: 0.2
  • shells: 0.8
  • top/bottom: 1.2
  • infill: 0
  • speed: 40
  • temperature: 230

 

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Because I am still trying to get a feel for the combination of speed and temperature. I wanted a high quality print so the speed is pretty low. And since the filament was rated with a relatively high melting temperature and because I wanted to reduce blobs that form due to too much pressure, I have chosen 230°. Still got a few blobs though. So I have no fool proof method for completely eliminating them.

 

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Are you absolutely sure that your filament is feeding smoothly...? I find that most if not all of my non-repetitive horizontal bands in prints are due to the filament not feeding smoothly off the reel, resulting in areas of slight, relative, under-extrusion until the tension on the filament is enough to pull it free again off the reel.

I really need to try and come up with an improved feed mechanism....

 

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I gave up on the filament coming off the spool gently a week ago. I'd hear the SPROINNNNNG and plastic crinkle of PLA popping off the spool and causing all sorts of neat knots. Now I have it on the floor under the table, so it gently pulls upward and gravity tends to reduce the tangling I was seeing.

 

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I think you should get a magnifying glass and look at the blue head carefully. Those lines in the blue head could be either:

1) Z stage moved down too much and so that layer got underextruded because the gap is taller.

or

2) underextrusion - potentially filament get stuck but layer is same height as other layers.

You can tell the difference because if it's #1 then the layer that looks like underextrusion will actually be a taller layer. And if it is #2 then the underextruded layer will be the same height.

 

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@illuminarti: Good idea, I'll check the spring tension on the feeder. I measured it a while ago and it was still at ~11mm. I also noticed that while assembling the extruder the plastic part that is pushed down by the spring sat very very tight on the contraption. I didn't believe at first that the spring would push it down at all.

@gr5: It is a baloon powered jet car :) (printed at 0.2 layer height). http://www.thingiverse.com/make:49558

Great idea about checking it with a magnyfing glass. Gota buy one - it is incredible but we don't have one here (I guess we are not old enough :) )

 

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It's not so much an issue with the feeder, as with the reel.

if the filament starts to get tangled at all - especially as the reel gets used up, and the radius of curvature of the filament is tighter, while there's more room for the filament to move around on the reel and get stuck between other loops of the filament, it can become hard to pull off.

Try pulling a meter or two of filament off the reel, and then letting it coil back loosely... and ideally keep doing that every so often so that the extruder never has to pull the plastic too hard.

 

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Btw, I highly recommend a loupe like this...

 

Or you can get "reading glasses" at any pharmacy (that sells bandages?). At least in the USA you can get reading glasses for less money than a bottle of wine.

 

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Alright, the magnifying glasses arrived. The layers seem to be the same height. So it might be underextrusion then:

zombie hunter 0.2

But some layers look weird, like the layer diameter changes. Also these plastic strands look bad and are not uniform:

zombie hunter 0.2 2

Could this be caused by too much movement of the bed?

Here is another print at 0.1 layer height. The layers here look alright except for some weird effects (huge blobs vertical ripples). I did print it fairly hot though (240-250° and 60mm/s speed).

zombie hunter 0.1

 

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Nice pictures.

1) Use your magnifier to look at your nozzle hole carefully. Is the hole round? Does the nozzle have a chunk missing from the tip?

2) Possibly water in the filament could cause this maybe? A pocket of steam adds extra pressure and pushes a little extra filament out, then a few seconds later you are underextruding when the steam pocket comes out?

- George

 

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My guess would be that the variability is due to variations in filament diameter, and the vertical effects may be due to local over-extrusion due to the head continuing to ooze at times where the head's linear speed is slowed to negotiate some complicated geometry with lots of short line segments.

 

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@George: The nozzle looks alright. Nothing missing or deformed. I have also watched some prints for prolonged periods of time (the fascination does not wear off, even after two months) and I don't see or hear the typical hiss and bubbling from bad filament.

@Simon: The filament in question is from Ultimaker. The blue one has a diameter of 2.85 and varies a bit. The white filament is also from Utimaker with a diameter of 2.94. This one varies more than the blue one.

So to sum up - this could really be just bad luck with inferior filament in combination with complicated objects. I have only printed with filament from Ultimaker because my old filament scrapes were very old and had worse diameter fluctuations than the Ultimaker stuff.

I'll try colorFabb filament next - let's see how that goes (will print the same objects with the same settings).

 

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It's not so much an issue with the feeder, as with the reel.

if the filament starts to get tangled at all - especially as the reel gets used up, and the radius of curvature of the filament is tighter, while there's more room for the filament to move around on the reel and get stuck between other loops of the filament, it can become hard to pull off.

Try pulling a meter or two of filament off the reel, and then letting it coil back loosely... and ideally keep doing that every so often so that the extruder never has to pull the plastic too hard.

 

To reduce friction inside the bowden tube, as an experiment you could also try to spray a tiny bit of oil/sewing machine oil in the bowden tube. It is recommended for flexible filament, and i have not noticed any side-effects in the print.

 

Alright, the magnifying glasses arrived. The layers seem to be the same height. So it might be underextrusion then:

 

But some layers look weird, like the layer diameter changes. Also these plastic strands look bad and are not uniform:

 

Could this be caused by too much movement of the bed?

Here is another print at 0.1 layer height. The layers here look alright except for some weird effects (huge blobs vertical ripples). I did print it fairly hot though (240-250° and 60mm/s speed).

 

250°C sounds very hot, for 60mm/s. I think 230°C should be sufficient. If your filament is not extruding properly at this temperature, maybe there are different problems. (Or your temperature is not displaying properly. Have you ever tested this? Do you have any indications this may be the case?)

I believe we offer high quality filament, but of course a flaw can occur.

Can you measure on about 5 different spots with a pair of digital calipers? (try to have some meters in between).

What are your measurements?

You could also try faberdashery, I solely here positive stories about their filament.

And personally, I never focus on the 11mm the spring needs to be tensioned at.

I always focus on the amount of friction I receive from the spring and filament.

Would be great to finally get this wobble of the table, right Nico?

 

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To reduce friction inside the bowden tube, as an experiment you could also try to spray a tiny bit of oil/sewing machine oil in the bowden tube. It is recommended for flexible filament, and i have not noticed any side-effects in the print.

 

Interesting idea about reducing friction inside the bowden tube. But from my quick tests, the friction seems to be fairly low (just moved the filament up and down in the bowden tube). It depends on the filament diamether of course. But apparently the filament I own is not problematic in this regard.

 

250°C sounds very hot, for 60mm/s. I think 230°C should be sufficient. If your filament is not extruding properly at this temperature, maybe there are different problems. (Or your temperature is not displaying properly. Have you ever tested this? Do you have any indications this may be the case?)

I believe we offer high quality filament, but of course a flaw can occur.

Can you measure on about 5 different spots with a pair of digital calipers? (try to have some meters in between).

What are your measurements?

You could also try faberdashery, I solely here positive stories about their filament.

 

 

I have not tested temperature readings thoroughly. Only briefly with a cheap ir/laser temperature probe.

And you are right about the filament. I measured it but apparently did a poor job at first because after I did it again the diameter is pretty stable at 2.94mm.

 

The wobble problem is pretty much gone. I fiddled with the brass nut holders and got it to fit perfectly centered on the z-coupler at the bottm.

 

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