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codeczombie

Pretty bad artifacts on modest overhangs

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Hello,

I'm pretty ok with everything when printing stuff, I can deal with huge printing time (part of the game) but when it comes to overhangs, there come the nightmares.

So I did a "pre-print test" to check if the slight overhang that even Cura didn't bother to mark (see image) was a problem (as usual) or not.

Overhangs Cura

I did the first print at 50mm/s speed and came out pretty awful on the stone's ovehangs and then I tried at the same settings but at 30mm/s speed.

It obviously improved on the "bump" side, but the overhangs came out almost the same, or even worst, not to mention the "melted" top of the stone.

Modest overhangs with pretty bad problems

Modest overhangs with pretty bad problems

Modest overhangs with pretty bad problems

 

At the moment I don't know what to do to manage this stuff, any hints or help would be very appreciated.

These were the settings, for 215°C nozzle temp and 70°C bed temp.

Settings

 

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More cooling is the ticket in this case I think. You're printing very very thin layers on a small area which means the head is spending a lot of time in basically the same spot and transferring heat into the part. This is why the top looks melted and it's making the overhangs worse.

First I'd drop the bed temp to 60C, that'll remove 10C of heat right off the bat. I'd also make sure the fans are going full blast. Perhaps lowering the print temperature a bit could help as well.

Then I'd try to enable cool head lift. I haven't personally tried it, but it sounds like a good idea in principle. If that doesn't do the trick I'd print either a second copy of the object or something else, at the same time. This means the head will move away from the delicate print for a little while and allow fresh cool air to cool it down.

And unless absolutely necessary I'd bump it up to 0.6mm layers, but that's up to you. You'll save quite a bit of time and I doubt you'd see much difference.

You could also consider skipping the infill completely. Increase the top layer thickness a bit and you shouldn't have any problem printing this as an empty shell.

 

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The Cool Head lift option will help i think. Either that or print another object of the same height at the same time will reduce the melting a Robert suggested.

From my small experience 0.06mm or even 0.08 gives a pretty good result. I'd also reduce the temperature to around 200°c if you print at 30mm/s it will probably give better results also.

[Edit]

Your test print looks pretty small too i guess you will print it bigger, the melting should impact the result less if the area is bigger

 

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Thanks for the hints.

I'm now printing a test with settings as you both suggested.

- bed 60°C

- nozzle 200°C (except for the bottom layer, which I usually print at 230°C for a better adhesion, as suggested by Gr5).

- 0 infill (very curious to know how it will end up)

- 0.8 Top/bottom thickness (before was 0.6)

- cool head lift enabled

"Unfortunately" I have to print at these (small) sizes so 0.04 makes a difference (compared to 0.06) since the finished piece must be really smooth and the last one I did I had to sand it for 3 days to get a smooth finish.

I'll let you know in a couple of hours. ;)

 

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This should be easy! I've done 45 degrees on a UM1 and it had zero bumps. Quality was excellent. UM2 also. Usually the bumps on overhangs are temperature related but in this case... I think not.

The 70C will only affect the bottom 10mm or so and this is an issue higher up.

My first thought was: temperature and speed - keep it cool and slow. But again - I don't think this is the problem. Unfortunately I think it's your layer height. Just for the hell of it, print this at .1mm and .2mm and I think you will see HUGE improvements. STUNNING improvements. Please do it as a test. For me. Thanks.

 

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The very top can be improved with cool head lift, yes. That tends to add it's own problems but it will be a big improvement. Even better is to print a tower over to the side where the printer goes over there to print something thus giving the very top of the rock time to cool. (is it a rock?)

 

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Well, updates.

These is the latest print according to IRobertI and Didier suggestions.

The biggest improvement is on the rock (yep, it's a rock, Gr5) due to the Cool Head Lift but it messed with the filament that was keeping to extrude a little while waiting the cooling and each time the nozzle was going back to the piece, it left a small amount of filament on the side of the rock (I had to remove it manually, but no big deal, compared to the previous).

I still have the overhangs issues, as suspected from Gr5.

BTW:

- Increasing the thickness and avoiding the infill was OK.

- Cooling the temperature to 200°C was OK, since I notice a smoother surface (see nose) than the other print at 215°C.

- 60°C bed temperature didn't look to help.

Overhangs test

Overhangs test

Overhangs test

 

At the moment I'm printing at the same settings as the latest one but at 0.1mm layer thickness as suggested by Gr5.

Will post the results in an hour or so, but if this is the problem, I'm doomed, since I need the highest resolution possible in order to give me less work for the post-production treatments (see days of sanding).

Thanks!

 

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OK, this is the print at 0.1mm Layer thickness.

Overhangs

Overhangs

Overhangs

As you can see, no improvements and an overall quality drop due to the lower resolution at 0.1mm.

I cooled the nozzle at 190°C, bed was back at 70°C as usual.

Top of the rock is OK, 190°C + cool head lift worked properly.

But for the overhangs it didn't help that much.

Fact is that, while printing the lower part of the rock, you can clearly see that the piece will come out messy because it's like rubber or "chewing gum" being "moved" by the nozzle, it doesn't stand flat but it raises a bit so when the nozzle makes its turn and come back to the beginning of the layer, it pushes it down, this for the whole round.

At this point I really don't know what to do.

 

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bed was back at 70°C as usual.

 

I really don't think that's a good idea. It's probably mostly unrelated but 70C is only useful if you have curling/lifting/sticking issues. And you dont. So 50C is plenty. Unless the part is lifting off the bed and all other methods fail, or if you have other shrinkage issues. This is not a shrinkage issue. It's the "raised edges" issue discussed here:

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

Especially look at the second video which is on page 2 of videos which shows the problem in slow motion.

I'm really not sure what the fix is. But I have printed parts like this with no problems. So I am very confused. I guess maybe it's time to try a different filament? Here are settings I used to print a perfect 45 degree all-around overhang very similar to your rock:

.2mm layers

.8mm shell

infill 20%

50mm/sec

fan 100%

There should be zero bumps! Surface should be beautiful!

Lower your part more into the bed so you don't have to wait so long for your test. No need to print the whole thing.

I really have a strong desire to do more "raised edges" testing but I am so busy with other stuff right now!

 

messy because it's like rubber or "chewing gum" being "moved" by the nozzle

 

I'm not sure what you are describing as this could be 2 different things:

1) It could be the raised edge issue described in my link above where the outer edge is pulled inward while it prints. It's like it sticks to the head as it goes around corners and is pulled inward, then it cools and the lip is too high in the air.

2) It could be that other layers haven't cooled enough before the head comes back and prints the next layer or pass. Infill might help with this to give it time to cool.

 

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Rereading that "raided edges" thread I see once more that fans are critical. I'm wondering if something is not right with your fans. For me the fans helped a lot. Maybe your fans are hooked up backwards and they are sucking instead of blowing. Check the airflow.

 

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You totally got the point, gr5, those videos show what's happening and what I tried to explain with my limited english.

I'll run some tests tomorrow with your settings.

When I ordered my UM2 some months ago, I also bought 4 spools of filament but, guess what, at the time they delivered the printer, both PLA and ABS where unavailable, so now it's more than 1 month that I'm waiting for new filament and I'm using a spool they sent me for testing with the printer.

So, after they changed the backorder for the filament from "beginning of april" to "end of april", I went on Colorfabb and bought 2 spools of white PLA, I just got a mail from Colorfabb where they say that they just shipped the order, if I only knew before, I wouldn't have lost all this time waiting for the filament from Ultimaker.

BTW, as soon as I get the new filament, I'll try some new prints.

Thanks for the link and infos.

 

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Holy!

Trying it right now with new specifics as you suggested: 190°C nozzle and 50°C build plate.

Will tell you in an hour or so.

The start of the print looked way smoother, slicing of the model looked way faster than previous Cura version.

Let's hope for the best!

 

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I also have overhang issue, to an extent, I just accept I'll be filling and sanding.

I'll post some not so good results now.

 

 

Braddock, are you telling me that, after 1 month trying to fine tune for a decent print, with Colorfabb it will all be lost??

Looking at your prints on IG, I see you almost don't have overhang issues, I really don't understand how it is possible.

 

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I had a similar problem.

What helped was setting "minimal layer time" to 30 (might need even more depending of model)

Second thing that helped was increasing "shell thickness" to 1.6mm. When using a shell thickness of .4mm, bits from the fill pattern ran into the overhanging part ruining the overhang.

 

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