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mvo

nozzle touching surface: Z-movement problem / too much material?

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Hi everyone,

I've got a problem with my quite new UM2 - perhaps someone can push me in the right direction, because at the moment I have no clue where to start searching. After successfully printing some small tests, I went for some bigger parts:

All printed with a high resolution (layer height: 0.06mm) at a quite low speed (50 mm/s; 70mm/s for the infill; 10mm/s for the bottom layer).

The start looks fine, however, when the print reaches a height around 5-10 mm the nozzle starts to hit the surface. The first time I didn't really realized that fact, because the overall height of the object was around that size. The result were massively pillowed top layers, because the infill didn't get covered but rather a 'hairy edge' was added.

The second time i could hear the nozzle slightly sratching over a previously printed top layer (when moving), the following layers get distorted. In this case I quickly turned the 3 screws at the printbed a bit to not damage the mechanics. As this did not help, the print was aborted.

My first thought was that too much material gets extruded. I'm printing with the blue ultimaker filament 2.85mm². I printed the extrusion test cone (http://umforum.ultimaker.com/index.php?/topic/3976-almost-always-missing-layers-underextruding/page-8&do=findComment&comment=33427) with a filmament diameter setting of 2.80mm², which resulted in under-extrusion after 2cm of printing. Resetted it back to 2,85 and it went up quite well (after the '7mm/s' mark the feeder starts clicking and jumping back and there is underextrusion in the object).

So where can I tweak the printer - could this be a problem with the z-axis movement? Or is this a common problem with small layers?

Thank you in advance for your input.

Moritz

PS: By the way: There is no problem with the object peeling from the glass surface - had this at the corners first, but a brim solved it. So this should not be the reason...

 

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Usually I only get the nozzle hitting the layer below when there are overhangs and only in those regions. There is a lot of discussion. There are a few possible fixes - the most common and most successful is more fan. But I suggest you read over some of this:

http://umforum.ultimaker.com/index.php?/topic/4094-raised-edges/

Look at the first picture in the first post to see if this is the same problem you have. Then skip right to "page 2" and look at foehnstrum's video and read all the posts after that possibly. It's not until around post #39 and later that we really begin to understand what causes the issue. That video was important and looking with "reading" glasses.

 

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Thank you for your resonses.

The objects I was printing were of a simple block-ish structure - no overhangs and no visible up-bending of whole parts like in the video. Also the fans were already running on 100% when printing the top layers :-|...

The reason it looks pillowed is due to the nozzle crashing in the topmost layer of the infill when trying to overspan the holes. As a result there are no continuous strings but a hairy edge is created. And yes: After some layers this border curls up (see the following picture for a closeup).

scratchy_surface.jpg

What looks like a deformed bottom is only the rest of the brim not properly cutted away - the lower structures are perfectly even. This image is kind of extreme, because that is after manually lowering the platform a little bit during the print (see the horizontal lines that look a bit under-extruded) and drastically reducing the flow at the end to prevent damage.

Perhaps I try printing a solid and a 'infilled' high test block to see when the problem occurs and if it has something to do with the infill. What do you think?

 

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My feeling is that .06 layer depth, 20% infill and 70mm/s print speed are not a good match. IMHO for the geometry you have there I doubt that using such thin layers will give you any advantage. I suggest you go to at least .10 layer depth, raise your infill to 40% and drop your print speedS to 30mm/s. That will probably fix it and then you can take it from there. No idea what your extruder temp. is but you can probably get away with the same temp. for those changes. Personally I would print them at 200-205 depending on filament (never used UM blue).

 

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Hi, thanks for your advice. I will give it a try today and then let you know.

(My nozzle temperature is currently set to 210°, previously 220° - I will have to experiment with lower values. Shortly I had some problems with a clicking/slipping feeder stepper and had the feeling that slightly raising the temp and current helped to avoid that problem. But it could have been the way the filament was rolled up as well.)

 

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Nope... :(

uneven-top-layers1.jpg

The top layers of this plane are completly messed up (image above: after ~3layers, image below: after ~6layers). I think it is the nozzle touching the surface.

uneven-top-layers2.jpg

A lower plane on the same object (~1,5mm from the ground) got printed without that effect. This one sits 0.9mm higher....

What could this be? I am printing with 40% infill, 0.1mm layer height, 0.8mm shell thickness, 0.8mm bottom/top thickness at a speed of 30mm/s...

 

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Thank you! These are good aspects.

1) I just measured the filament. Seems to be around 2.9mm rather than the specified 2.85mm - so that might be the reason for the over-extrusion. In the current print, I therefore reduced the flow to 98% in the tune menu. If I understand correctly this should compensate the over-extrusion? (Before the next print I will then try to adapt the filament size property. At the moment I don't understand how flow/diameter/... interact - are these all parameters for the same property?)

2) I did not lower the temperature before - so probably the transferred amount of heat was bigger (because the nozzle sits over the parts for a longer time). Good point. I try to reduce it to 203° now.

 

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Obviously there is a HUGE difference between the photo in post #4 and #9. It looks to me like a huge improvement. You gto rid of the pillowing completely.

There are hundreds of printing issues. Please don't confuse the 2 issues above with each other. I'm pretty sure any problems in post #9 is completely different than issues in post #4.

I doubt there will be any difference between printing at 210C versus 203C.

Also printing 40% infill should be unnecessary. I usually print 20% infill and never get pillowing. The 30mm/sec and the .1mm layer is what I believe fixed the pillowing.

Now what is the problem with your latest print in the latest photo above? Is it the central area that is a problem? Or the border? I have to say that I have no idea what is going on at the border. That looks like infill for walls that haven't been printed yet. Is that correct? I'm going to guess that's not the problem, right?

So the problem is in the center area? Can you explain the problem better please because it looks like a huge improvement over photo in post #4.

 

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Hi,

yes you are right - there is a huge difference, but the height of the planes differ as well. It seems to get worse the higher it is (which led to my first over-extrusion assumption).

Look at the photo below. Its the same model (around the same printing stage, still in progress) - but the version above is printed with 203° instead of 210° and a flow setting of 98% instead of 100%. However, I also changed two parameters in cura: I reduced the infill to 30% (instead of 40%) and disabled combing to get rid of the crossing strings through the infill.

I keep on watching, but maybe the last changes did the trick. (Uhh, and don't look at the glue fragments below the current print ;-)...)

version_b.jpg

 

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Hi I think you mean " the version BELOW" printed at 203? I would normally agree with George that a difference in temp of 7 degrees is not going to make a great difference BUT I have found with whites that reducing from 210 to 205 can make a large difference, in terms of correcting over extrusion. Reducing from 40% to 30% infill will not improve your print - but may make no difference either. It has been my very limited experience that using a layer height < .100 can prove problematical when covering sparse infills with solid layers. With .100 you may even get away 20% infill but I do not really know as I normally use 100% and never go below 40%. In certain cases 100% gives you faster speed as there is no retraction. I do not use the flow setting either :)

I think you said you were using solid layers for a depth of 0.8mm. If you want to go to thinner layers I think you will find that increasing that to 1.2mm minimum will help (to a certain extent dependant on the infill %)

Anyway the last picture looks good so pleased to see that you seem to have got there!

 

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... of course it may be that that has nothing to do with it. Take the filament out of the Bowden and run your finger along it- if you have very noticeable teeth marks then your drive wheel is set too tight and continuous retraction will almost certainly give you what you have just experienced. The filament in my Bowden tube is pretty much as smooth as the filament waiting to go into the Bowden tube

 

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Hi everyone,

there are already a bunch of very helpful infos in this thread! Thank you all!

First of all, I was able to finish the print in the 3rd attempt. I therefore had reenabled combing (to reduce the amount of retraction). To see what difference the infill rate makes I also lowered that value to 20% again. I lowered the printbed temp to 50° after printing the first layer. To me it seems that having the bed at 60-65° and printing very slowly (50%) for the first layer results in good adhesion, so thats why I started a little bit higher.

case-1.jpg

Finished. And right after that, I printed the top part...

case-2.jpg

Yei.. fits! :-)

case-3.jpg

And now for the BUT part:

Blame it on the infill*?

I think there is still overextrusion happening. The filament diameter is already set to 2.9mm - should I increase that value or adapt the flow as the filament is not thicker than that? (Does this make a difference?) I also think of lowering the nozzle temp to 200° for the next test. I have the feeling the temperature was the main course for the too high layers. Even if it was only 7 deg difference.

When the infill (20%, so the '<25%'-algorithm) was ready to get covered, the nozzle again crashed into it. I could hear and feel the vibration of the printbed. The depth, however, was not too critical, so the filament strings made their way over the holes. After a while the effect was gone. The '>25%'-version seems to be less critical to the problem. I'd love to have a parameter for the flow that only affects the infill... I would lower it a bit. The next part I'll be printing will be 1-2cm higher, I hope not to get the effects of the image in post #4 again then.

*) it is a bit off-topic (maybe?), but I am not completly happy how the infill is layed out by the algorithm: Assume you have a shape like the box (image above). When the infill is layed out it covers both the bottom part and the wall parts. When the bottom part then gets closed the strings end in mid-air because, at the xy-pos where the inner edge of the walls will get put on, there are holes from the infill under it. Not good, because this leads to a slightly curled/not nice edge of the bottom part. Although this effect evens out after putting lots of layers onto it, it is not ideal and it would be better if at least the outer line of the plane of the first covering layer would be put on as a continuous one. What do you think? Or are there better option to circumvent that problem?

Grinding and the feeder

My material has 'bite marks' on it after leaving the feeder unit. Not too severe, but could be less. On the other hand the pressure is already set to near-minimum. I wonder how a 3mm filament will work then... Ok I have to tweak that part. To get rid of the feeder clicking I raised the current to 1,3A and put the filament roll at the floor and unrolled a bit of it (to get a bigger radius). That looks like a much easier job for the feeder than on the back of the device. A bit less pressure for the next print, now.

Is there a way to tweak the retraction settings, that no grinding occurs? Like "please don't retract the same 5mm of filament 1000 times" - this should be easy to simulate from the gcode. And well, taking 100% infill might be a working solution in some cases ;-). Good point.

 

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Personally I would print a test cube at 200 and then again at 195. I do not know the characteristics of this blue filament but .100 at 30mm/s with 200c is OK on most of the filaments I use. See how low you can go then give that temp. a try.

It may be that 40% infill will not cause retraction, it will depend on the geometry and object size; worth a try, you can always kill the print after a few layers.

Most of the stuff I print is smallish engineering items and using 100% infill neither adds significantly to the time or the material used so it is not a subject I ever really think about. I did print the base for a building which almost covered the entire bed and I used 40% for that, which probably gave similar spacing to the holes in your 20% print. I did not suffer the problem you are finding; I was using .200 layer depth

 

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