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doktrmike

Nice smooth layers get rougher during print

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This may not be an issue that's limited to Cura, but since I was using it to do this print, I thought I'd post here to see if I can get some help. I'm still fairly new to printing. I built my home-grown MendelMax recently and have been using Slic3r until recently trying Cura (using v13.11.2).

When using Slic3r I got nice clean prints but gaps were left between the perimeters and also between solid infill lines in the top layers. I spent some time messing with the settings but wasn't able to get the upper surfaces to be smooth and solid, just smooth. Here's a pic:

https://drive.google.com/file/d/0B9pUEQQWjpRQUFZrdk5oN3Y0UE0/edit?usp=sharing

Now I've started using Cura, I'm having a different issue. The bottom layers are nice and smooth, but when it lays down solid top layers on the infill, the surfaces are far from smooth. Here's a pic of a Tardis model that I'm working on:

https://drive.google.com/file/d/0B9pUEQQWjpRQVlNEaHQ1ZTVQTGc/edit?usp=sharing

I aborted part way through after noticing the way the upper surfaces were turning out.

This also happens with much simpler models, like a simple cube. I can't post my full settings right now, but am using a 0.5mm extruder, PLA at 180C with a heated bed at 65C, layer height of 0.2mm, 1mm perimeters and 0.8mm top and bottom solid layers.

Any help greatly appreciated. I really like Cura so far and want to figure out how to get nice prints!

-Mike

 

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It's difficult to compare temps across different printers, but 180 is quite low for PLA; particularly when printing with thick layers - so depending on the throughput capability of your extruder, and the linear speed you are printing at, you might get better results printing at a higher temperature. Certainly the rough finish you're seeing there looks a lot like your smearing PLA paste onto the print, rather than extruding smoothly.

One of the differences of Cura is that it doesn't really provide any kind of interface layers between grid infill layers and the solid top surfaces. As a result, the first few layers on the top of objects tend to go down poorly. But if you give it more layers - I'd say at least 5 - then you can still get a smooth finish on the top.

Regarding the issue with Slic3r - I'm not really sure what is going on there. One thing to be wary of with Slic3r is that you really need to manually set your extrusion widths (=nozzle width) otherwise it can do some odd things that may over load your extruder; the resulting under-extrusion might cause the gaps you're seeing.

 

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Thanks for the guidance. I tried a higher temperature (210C) and things did seem to be coming out smoother. My first tests sliced using Cura had nice smooth upper surfaces.

However, after a short time I started to get pretty big blobs every few layers. The extruder would just spit out a blob around 2mmx2mmx2mm or so and continue printing. I tried various prints but this issue didn't go away. Could the higher temperature be causing this? I didn't have an opportunity to drop the temperature and try again yet.

 

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No, it shouldn't be causing those sort of problems unless your temperature readings are way off and you're heating the plastic to the point that it's breaking down and giving off steam or other gases. Or perhaps your filament has a lot of moisture in it. But I live in a humid place, and don't have that sort of problem, certainly not at 210º.

Do the blobs always happen in the same place? I wonder if its a gcode issue... could it be, for instance, that your printer isn't able to retract at the speeds that you ask for, so when it tries to de-retract extra filament gets pushed out of the extruder?

 

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Do the blobs always happen in the same place? I wonder if its a gcode issue... could it be, for instance, that your printer isn't able to retract at the speeds that you ask for, so when it tries to de-retract extra filament gets pushed out of the extruder?

Wow - I like that theory. Unless the filament is wet of course.

DoktrMIke - I recommend an experiment. This will help you with other issues as well as it provides you with a new set of tools. Download pronterface. It's free. Go half way down this page:

https://github.com/kliment/Printrun

And follow the installation instructions. Hmm - I got a different simpler version from somewhere.

Then experiment with max speeds for the extruder. It used to be that if you asked for 40mm/sec you got 20mm/sec but if you asked for 20mm/sec you got 5mm/sec or something like that but there have been changes in the firmware (not in Cura though) and if you somehow got the latest Marlin 40mm/sec is much too fast. My max speed is 25mm/sec for the extruder and it seems fine so when I ask for 40mm/sec I get 25mm/sec (I have the latest Marlin).

You need to learn the gcodes for setting the feedrate (F) and for setting max speed for extruder:

http://reprap.org/wiki/G-code

See M203 as in:

M203 E25

Sets extruder to 25mm/sec max so if you ask for 40mm/sec then it only goes 25mm/sec. BUT DON'T DO THIS PERMANENTLY for marlin that comes with cura as that one has a bug and 25mm/sec is much slower than you want.

Anyway you also have to save your final max speed which you can do with ulticontroller or with printrun:

M500

If you don't do M500 then when you power cycle it will go back to the previous values.

 

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This may not be an issue that's limited to Cura, but since I was using it to do this print, I thought I'd post here to see if I can get some help. I'm still fairly new to printing. I built my home-grown MendelMax recently and have been using Slic3r until recently trying Cura (using v13.11.2).

When using Slic3r I got nice clean prints but gaps were left between the perimeters and also between solid infill lines in the top layers. I spent some time messing with the settings but wasn't able to get the upper surfaces to be smooth and solid, just smooth. Here's a pic:

https://drive.google.com/file/d/0B9pUEQQWjpRQUFZrdk5oN3Y0UE0/edit?usp=sharing

Now I've started using Cura, I'm having a different issue. The bottom layers are nice and smooth, but when it lays down solid top layers on the infill, the surfaces are far from smooth. Here's a pic of a Tardis model that I'm working on:

https://drive.google.com/file/d/0B9pUEQQWjpRQVlNEaHQ1ZTVQTGc/edit?usp=sharing

I aborted part way through after noticing the way the upper surfaces were turning out.

This also happens with much simpler models, like a simple cube. I can't post my full settings right now, but am using a 0.5mm extruder, PLA at 180C with a heated bed at 65C, layer height of 0.2mm, 1mm perimeters and 0.8mm top and bottom solid layers.

Any help greatly appreciated. I really like Cura so far and want to figure out how to get nice prints!

-Mike

I just had to register after seeing the first pic. Try this:

Print the same object twice with some distance between them an lower your speed. To me it looks like the PLA cant cool down enough after one layer...

 

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Thanks for the suggestions. I tried a series of prints of a small cuboid (24mm x 12mm x 4mm) last night and got some decent results. The first thing I did is went back and made sure my bed was level, which I think it was not quite. Then I printed the cuboid using 0.2mm layers with following settings:

1) No retraction, 185C, 3 top/bottom layers, 20% infill

2) No retraction, 185C, 5 top/bottom layers, 50% infill

3) Retraction on (default), 190C, 5 top/bottom layers, 50% infill

4) Retraction on (default), 195C, 5 top/bottom layers, 50% infill

#2 was much better than #1. #3 was marginally better than #2, and was about the same as #4. I didn't see any blobbing issues in any of the tests. In #3, the top surface was pretty smooth, although there are still small gaps between the extruded lines, especially at the interface between the infill and perimeters.

I'm going to try a larger, more complex print with the #3 settings and see how it goes.

 

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What's a cuboid? It doesn't sound like something that has retraction.

 

In #3, the top surface was pretty smooth, although there are still small gaps between the extruded lines,

 

Please post picture. This could be underextrusion or play or cooling issues - a photo will say it all. Sorry if you already said: is this UM1 or UM2.

 

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A cuboid is a solid shape with 6 faces with a square or rectangle on each face. I tested with retraction because it was suggested above that these settings were causing the blobs. I recognize that it wouldn't make a direct different to the print.

I don't have a picture now but will post one later. I'm printing with a homemade MendelMax 1.5+, not an Ultimaker.

Thanks again.

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There were probably zero retractions for that part.

Well - it looks like serious under extrusion. Also the fact that your wall is wiggly is scary - makes me wonder if you parts are loose or if your rods are straight or what - something is all wobbly.

Anyway - the underextrusion is the main issue. This can have many issues. I'm going to guess you are printing too cold. For a cube, where I don't care about retraction, I would print at 230C. Just try it and print the cube again.

You might have the extruder miscalibrated. I mean it looks like you are getting a flow of 50% (half of what is needed). Consider doing a test where you extrude 10mm of filament and see how far the filament actually moves. Make sure you do this nice and slow.

What speed did you print these cubes? 185C to 195C is quite cold and PLA tends to be like thick toothpaste at these temperatures - some brands/colors won't extrude at all at 185C although usually it's fine if you print slow enough and if your extruder is strong enough. My extruder can pull 22 pounds of force on the filament. Consider testing yours. At 190C I print slow: 20mm/sec. Because any faster and the risk of grinding the filament to dust with the extruder increases.

 

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The walls were wiggly because I took the part off when it was cold. I printed this keychain this morning:

https://drive.google.com/file/d/0B9pUEQQWjpRQZURxYWstWWtKZ0E/edit?usp=sharing

which looks neat to me.

I'm surprised to hear you say you think I'm underextruding. The bottom few layers are very smooth and neat:

https://drive.google.com/file/d/0B9pUEQQWjpRQTEhLZkNGRndQY28/edit?usp=sharing

The perimeter walls are very smooth as well - if I drag a nail along the side wall it feels smooth. I used Triffid Hunter's calibration guide to fix the extruder steps and I thought it was correct. I'm also printing at 20mm/sec for perimeters and 30mm/sec for infill. This keychain took 20 minutes with 0.2mm layers.

Edit: I guess I'm saying I'm not convinced the temperature or speed is the issue, since the bottom layers are so nice. Is there a reason why you'd expect that to happen if your thinking is correct?

 

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Ahh - good - I'm glad the keychain isn't wavy/wobbly and it was just because the part was still hot.

BOTTOM LAYER GOOD:

The homing height is hard to get perfect. .1mm is the width of a piece of paper. If your bottom layer is for example .2mm and your bed to nozzle distance is .1mm closer than you thought then it will in effect over-extrude and you will get a beautiful bottom layer. Maybe you aren't off by 50% - maybe only 30%. Maybe your bottom layer was 30% closer to nozzle than you thought (.066mm if .2mm bottom layer .1mm if .3mm bottom layer - by default bottom layer is thicker (.3mm) in cura to compensate for errors in leveling).

Also Cura tends to print the bottom layer slower than other layers. Although maybe not for this case. Plus if you have heated bed set over 70C that might help the plastic flow nicely into a thinner flatter layer. But I doubt it is this last thing - more likely homing height.

When I look at the top of your cuboids and keychain I see huge gaps. Almost as wide as the filament. It looks just like underextrusion. I wouldn't mind seeing a side view to see if the sides look underextruded also - that's a different look that is hard to describe. If (on the fly) you set flow to 200% you would get a nice beautiful top. Also your walls seems to have a gap between each other - this also can be caused by underextrusion (and other things).

How did you calibrate your extruder steps/mm? Was it something they told you to do in the instructions? There are jumpers on the stepper board and if you add or remove one the steps can be off by 2X.

 

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I don't have a picture to share right now, but the side walls are very smooth. Having said that, I've tried to print a single-perimeter cube with no infill a couple of times and have definitely seen underextruded walls (though I've been messing with so many settings it's hard to recall the circumstances).

To calibrate the steps/mm I measured a stretch of filament then extruded this distance using Pronterface. It matched up pretty closely, and then I tried to dial it in further based on the Triffid Hunter calibration guide suggestions. I'm using the value 760, though have tried up to 820 without seeing much improvement.

I don't really have instructions as I didn't purchase a kit. I'm going largely by MendelMax documentation that is freely available on the web.

Your comments have given me some things to try, however, so I'll do a few more tests and report back. Your link discusses backlash, which I might revisit since it could suggest an issue, although I agree that temperature and extrusion steps are worth examining further.

Thanks again for all your help so far. Much appreciated!

 

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I don't think that backlash is what is causing the underfilled top surface in your prints, because you can clearly see the lines that the head is taking, and it's not overlapping itself at all (which is what happens to cause the under-extruded surface look). That said, I do see some signs of backlash in your top surfaces - in parts, you get two lines closer together, then the next one a bit further apart suggesting that the head positioning isn't as precise as it could be for some moves.

if you could upload or http://mailto:gcode@fbrc8.com the gcode for the keyfob thing, I'd be interested to take a look at it, and see what sort of settings you're using, so we can eliminate slicing problems.

 

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Side view looks good - it isn't extremely underextruded but you can get 30% underextrusion and still have the sides look that good. I'm still going to go with "raise the temp to 220C or so". You might get better adhesion between the layers also (i.e. stronger part).

 

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Okay, folks. Some big improvements here.

https://drive.google.com/file/d/0B9pUEQQWjpRQVHBtUGJDQnRpQlU/edit?usp=sharing

I did a number of things to get here. Your comments and especially gr5's link to the effects of temperature and backlash got me thinking of the mechanical issues that could be hindering the prints. I think, like a lot of folks, I tended to want a software explanation when in fact there were hardware issues. Here's what I did:

1) Cleaned the hobbed bolt. Not terribly dirty but a number of PLA flakes embedded in the teeth.

2) Adjusted the position of the hobbed bold on the motor shaft. I checked the correct position based on the extruder I'm using and it was: a) not in the right position and b) a little loose. I got it in the right place and tightened.

3) Checked the voltage on the extruder Pololu driver. I had it set to what was probably a high value.

4) Tightened up the x-axis belt.

I then printed the attached at 185C using slow speeds. The first print using my existing e-steps value of 760 had some little gaps on top. I increased to 770 and printed the attached, which looks great and feels very smooth on top.

I take your points, gr5, about using higher temps for PLA, and will try going a little higher and experiment with the speeds as well.

I'll leave it to you guys to figure out which of the things I did probably fixed the issues, but thanks so much for your help getting here.

 

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Glad you got it working! One thing I will say - changing you esteps from 760 to 770 would have made no discernable difference to your print. :-) The variation in extrusion rates due to back pressure at higher speeds, and the natural variation in filament diameters normally can easily result in variation in extrusion amounts that can easily be in the 10-15% range, and it's usually pretty hard to tell any difference.

 

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