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sbob

Underextrusion when printing uneven surfaces

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I am having problems with underextrusion that are a bit different than the other recent thread about underextrusion.

I am trying to print a rather largish box for a CNC circuit board. With my normal settings it would take 15 hours to print according to Cura (Which probably means 30 hours IRL). In order to get it down to reasonable levels I have printed it at:

0.2 mm layer height.

90 mm/s

230C

0.4 mm wall thickness, 0.6 mm bottom and top thickness and 20% infill.

When first experimenting with these setting there was no problem at all printing a 20mm cube, it was even possible to print at up to 150 mm/s.

When I printed the box everything was OK to start with. However, the problems started when there were details and not only smooth surfaces. I got lots of ugly underextrusion, see picture. After the details it was back to smooth walls, but then it got even worse! As you can see in the picture the top layers are hopelessly under extruded.

While printing the top layers I tried to change the settings while it was printing to see what was wrong:

- I slowed it down to ~30mm/s - no change.

- I then looked at the filament and the extruder and changed flow up to 150% - it was making deep marks in the filament so I think it has strength enough but is slipping on the filament. The spool was running smoothly.

The funny part is that it was working fine until after the details halfway up. So it seems that my settings were ok.

Have there been any previous problems with the temperature regulation? Might the reason for my problems be the same as for random underextrusion? I would really appreciate some help. I could of course revert to printing really slow, but since it works sometimes it would be nice to not prinitng for 15+ hours.

 

Underextrusion

 

 

 

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1) um1 or um2?

2) This looks like it could be a slicing issue. Did you look at it carefully in cura layer view? If you didn't use cura try repetier host (it's free) to view the gcode. Remember that in cura layer view the blue lines are non-extruding lines. Look at the bad areas carefully in cura. Maybe post your gcode - upload it somewhere and post a link to it - and I'll look at it with repetier host.

I've seen underextrusion when you go from slow to fast but not this much! This is excessive.

 

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I suspect it's just due to the high pressure caused by relatively fast printing, and then when you slow down for the detailed bumpouts, the head oozes and becomes under-pressurised.

It would be helpful if you could post the gcode somewhere so we can take a look at it.

How big is the STL file that you're working from?

 

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It is a UM1.

I have posted the Gcode at:

https://www.dropbox.com/s/c6vtl7jye25u12y/CNC%20Foam%20cutter%20box%201.gcode

Checked the STL file and it is 1.9 Mb.

I also looked in Cura. There are more blue lines than I would have thought necessary, but since I have not looked that closely before it could be normal. Does it retract every time there is a blue line?

If I understant illuminarti correctly UM will slow down for details, and then behaves a bit like a caulking gun and oozes even though you stop pressing. That would explain the bad part after the little round hole. It also would explain why it then slowly gets better, as pressure builds up again. Still, would it not have done the same after the text in the middle? Or after the big holes?

Will try "Horrible settings" tomorrow.

 

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also would explain why it then slowly gets better, as pressure builds up again.

 

Well, yeah, but slowly is usually like maybe a half second.

So the problem should be very fixable by simply slowing it down. 30mm/sec should be slow enough. I'm confused though as you said you tried this already?? Are you sure? Maybe you have a fluctuating temperature? If the temp got down to 170 while printing at 30mm/sec that could also explain this problem.

I'm wondering if maybe you ground up the filament a bit and the extruder eventually "got lucky" and started working again.

I mean I have to admit 90mm/sec at .2mm layers at 230C is quite doable but on the fast side of things. Make sure your extruder spring is around 11 to 11.5mm long when closed on the filament.

You should just try it again but at 40mm/sec or so. No other changes - just lower you feedrate to 45%.

 

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Does it retract every time there is a blue line?

 

No. You have to enable retraction checkbox and you might also have to set the to "mm" distances to 0 in the advanced settings.

You can tell which moves have retraction because at the start of the blue line there is a vertical movement.

Of course you have to select that layer first with the slider scrollbar on the right side first.

 

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You can tell which moves have retraction because at the start of the blue line there is a vertical movement.

 

Just to clarify - the vertical movement is graphics only - it's just an indication, not a movement - the Z axis doesn't actually move. The extruder does.

 

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Actually.... it's not entirely fine...

Here's what I think might be happening... and it's related to what I was just saying over in the other forum about 'Combing' and retracting during internal moves....

I only looked briefly - but if you look at the code in Repetier Host, around 'layer' 219 ish - the layer is actually starting in the middle of the letter 'a' of the embossed 'Pa' in the upper corner - right by where the worst under-extrusion is in the middle of the photo. And it finished the previous bit of printing on the previous layer way in the back corner (to the right of the photo). So it did a long travel move all the way down inside that right side wall - without any retraction. So my guess would be that it was oozing all the way down there, so that by the time it started printing again, the nozzle was pretty empty, and so you get significant under extrusion around the corner and down the side until pressure builds up.

Additionally, it may not just be on that side that it's oozing, either. There are long travel moves along all the sides of the box as it's printing infill. The pressure has probably been dwindling all the way through infilling the walls.

So it's not that the lettering is causing the problem - it's that the lettering shifts the start point of the layer away from where it ended, because it sticks out a bit and basically tells Cura 'Start with me!'. And it does in on a layer that has a hole cut in it already, and so can't print as a continuous loop. So you get lots of long travel moves, without retraction to lower pressure.

Ideally Cura would get smarter about retracting during travel moves... but failing that, turning off 'enable combing' might help, if it makes it always retract on travel moves. Upping your travel speed might help too - 150 is quite conservative; you can probably got to 200 or 250: faster travel means less time for oozing, and more chance of the thread breaking rather than getting pulled out of the nozzle.

 

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Sounds plausible. Explains most of the underextrusion, probably also the parts between the five 7 mm holes on the back side. Why it started to underextrude completely in the last few layers is still a mystery though, although the filament looked a little gouged so maybe debris clogged the nozzle?

Did another print where I unchecked the combing enable option and increased travel speed to 200 .

Now it retracts a lot everywhere, leaving little knobs where it does. These knobs make the outer surface uneven, with some holes in it, and there is severe stringing messing up the holes so not a total success. The underextrusion got slightly better, but still showing the same type of patterns.

I guess I have to re-think how I print this thing. Either print slower or split it into several parts, the four walls and bottom printed laying down on the bed and then glue them together. Any ideas on printing slower, would it improve the underextrusion problem?

Second try

 

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As Illuminarti says, .8mm and turning combing back on should help with the bumps somewhat.

This is optional, but to improve the look even more you can lower the temp and lower the speed. If you aren't in a rush, try 200C and 30mm/sec and .1mm layers. It will take "forever" but it will look nicer. Don't lower the temp and keep the same speed though as 90mm/sec, .2mm layers is too fast for 200C.

You should add a brim also to reduce the lifting of the corners of this part. And clean your blue tape with alcohol. Those two things will keep the 4 corners from lifting.

 

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I liked the idea of hiding the underextrusion by adding another layer, making the side walls 0.8 mm thick. So I printed at 90mm/s and 230C, re-checked the combing enable option.

The result was that the added material amplified the warping problem so much that the print crashed. It was not that the plastic lifted from the tape, it was that the tape lifted from the plexi-glass print bed. I used a brim and when that was printed I added tape on top of the brim that I then folded around the edges of the print bed to hold it in place. No luck, it lifted the whole thing and tore the tape...

My conclusions from all this is:

1. Cura needs to both reduce the number of, often unnecssary, long travels and to add retraction in order to not loose pressure that leads to underextrusion. Or compensate in some other way.

2. Printing a box this large is not possible without a heated bed. Maybe if the temperature is set lower and print speed slower, but then it would take more than 30 hours to print it, in my case.

Luckily I have some of the parts needed to build a heated bed lying around so I might give this print another try some time.

Thanks for all the help, I have learned a lot about printing!

 

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Using the widest tape you can find will help, as will swabbing the tape down with alcohol - I think it helps the adhesive stick to the bed, as well as the print to the tape.

Also, you might try printing without the fan turned on; I generally find that the constant flow of air across the right side of the print over-cools the print, and makes the right side warp up in large box-like prints. A large print like this will take sufficiently long per-layer to cool, that the fan isn't essential.

 

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1. Cura needs to both reduce the number of, often unnecssary, long travels and to add retraction in order to not loose pressure that leads to underextrusion. Or compensate in some other way.

2. Printing a box this large is not possible without a heated bed. Maybe if the temperature is set lower and print speed slower, but then it would take more than 30 hours to print it, in my case.

 

Printing slower won't help the warping - just will help with the underextrusion because the pressure never gets very high in the nozzle.

Illuminarti uses I believe 6 inch wide blue tape - this helps a lot. I use about 3 inch wide tape. Much better than the 1 inch tape from Ultimaker and it takes less time to "tape the bed".

 

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I'm really new at this and take what I say with a grain of salt. I had a lot of problems with the blue tape not sticking the part to the bed. The tape would come off or the part would come off the tape. I started printing on glass with Elmer's washable school glue stick desappearing purple on the glass. No tape. Parts stick great! I now have a bunch of blue tape waiting for a painting job around the house.

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I'm glad you figured it out.

Blue tape needs to be washed with isopropyl alcohol to remove the waxy surface if you want pla to stick to it. And if the blue tape is not sticking to bed, it's best to use wider strips of tape - say 6 inch wide (although 3 inch works well for me).

 

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