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Kurniati

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This curved truss structure, almost 12" tall, took a total of 5 days, using Cura 2.3. There are blobs and stringing all over it. I have changed the temperature to 195C, Material flow kept at 100%. I am wondering if this is because of the retraction problem. The setting is as follow:

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Edited by Guest

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Here is a resource that may help you dial in issues.

https://www.simplify3d.com/support/print-quality-troubleshooting/#blobs-and-zits

Your temp might be a little low and you are trying to compensate in other areas that may effect print quality even more negatively... I would start with doing a smaller test print and start dialing in your printer settings.

Have you done any small print testing like https://www.youmagine.com/designs/hollower-calibration-pyramid to try different settings?

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Thank you STEMedTeacher for your reply.

I have not done the pyramid test for the settings before. I was using square cubes to test it out.

This is a test I've just done, changing the Retraction minimum travel to 1mm, instead of the default 0.7mm, travel speed at 120mm/s from default, combing is on, and temperature of the print as 200C. Then as it is printing, I change the retraction length from 6.5mm (where there's thin stringing visible) to 4.5mm of the default (where I started to spot long stringing forming) then I change it to 6mm after 5 layers of 4.5mm setting that shows visible stringing. 6mm retraction length works well at the beginning (after the last stringing at the center or middle-height of the print), but starts to show more stringing towards the end.

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The second print (a different model), has the same setting, except for the increase in travel speed to 150mm/s.

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Also could you check if you have the option to have acceleration/yerk controlled by Cura. I don't know if that's on the um2 but on um3 it can force very low accel/yerk while printing (making weird extrusion flow fluctuations) that IMO affect printing small areas at certain speeds.

Edited by Guest

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Yes. The acceleration and jerk controls are available in Cura for UM2. However, I hav never change the settings for it. May I ask how I should test it out? After my reply post to STEMedTeacher, the print starts to string again with the same settings I've mentioned in the reply.

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Well, those controls are disabled with the default setting.

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This is what happen when i use the default high quality print from cura, while I changed the Retraction minimum travel to 1mm, Travel speed to 150mm/s and temperature to 200C.

5a332337a3c24_IMAG47071.thumb.jpg.aa58f24089d109cc13dd68e05241a434.jpg

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Maybe you need to print just much cooler. Each pla & even color, has different viscosity.

I'm not a fan of um2+ feeder but for my prints using a bondtech gear I use 0.50 minimum extrusion.

Other setting that might be affecting (unlock by default) is the amount of retractions that can happen on the same area. Probably that also isn't helping.

Search for options under retraction and unhide them. You might need to tune them to have better print control. Also the temperature doesn't seems right.

Also travel speed should work perfectly at 200mm/s on any um2/um2+

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Oh also. Blobs can mean two things and sometimes is easy to confuse them (unless you see the how they occurred while looking at the printer and hearing the retraction etcetc to debug it).

A blob can happen because:

- Too hot, drip occurs too fast that the retraction doesn't stop it in time. This use to have also strings. This can be adjusted with better cooling + faster travels.

- Too cold. The pressure from the filament inside the bowden is too high that as soon the nozzle is near an open area the filament exists (because the pressure) leaving a blob near a retraction (because the retractions use to happen near a loop end). Printing the infill 'last' can help to hide this on the inside.

Ofc the option that can help is called coast at end (on s3d, on cura os coasting I think), this option stops extruding at the end of a loop allowing the drip to be part of the print. The problem with coast is that without proper control it can leave gaps on the layers. So it has to be adjusted to speed/temp/viscosity/sizeofblob.

Edited by Guest
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Maybe you need to print just much cooler. Each pla & even color, has different viscosity.

I'm not a fan of um2+ feeder but for my prints using a bondtech gear I use 0.50 minimum extrusion.

Other setting that might be affecting (unlock by default) is the amount of retractions that can happen on the same area. Probably that also isn't helping.

Search for options under retraction and unhide them. You might need to tune them to have better print control. Also the temperature doesn't seems right.

Also travel speed should work perfectly at 200mm/s on any um2/um2+

 

What do you mean by the incorrect temperature? I have it set at 200C, which is within the range of the suggested temperature for ultimaker PLA.

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Temperatures for pla or other filaments depend highly on the speed/layer height (mm3/sec) so if you want to print faster you need to increase the temp and if you print slow you can decrease it. There's no 'perfect temp' for all mm3/sec. 200 is a reference. For example I print 195C for 0.1 40mm/s (on a different system than yours) but for 60mm/s and 0.2 layers I print at 225C.

Edited by Guest

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Increase your print speed a bit I think. I've had printers for a few years now and I've never printed that slowly. 6mm/s on the outer walls is way overkill and will give you worse results than going faster. The nozzle is moving so slowly over the print that it's overheating the previous layers. Try something like 30-35, that's still fairly slow but the plastic wont turn super liquid in the nozzle.

That, or decrease your temperature by 20C or something along those lines and see if that helps.

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As Nicolinux says: even within one brand and product range, some filaments have totally different stringing characteristics. For example in PLA/PHA from colorFabb: the "olympic gold" and "natural" colors do string more than standard white I had. Probably due to the amount and sort of fillers used? Ultimaker's "Pearl" (nice color by the way) also strings a lot. But they do stick very well to the build plate.

ICE PLA strings far less, also prints nice, but does not stick so good to the build plate.

Also, the sticky and "stringy" materials are more difficult to grind: the molecular structure appears to be more fibruous (I don't know if that is a good English word?), thus containing longer fibres. While the PLA from ICE grinds into a fine powder. I can imagine that the longer fibres in the molten material increase stringing.

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White PLA (doesn't seem to matter who makes it) is like this - much more difficult to print. I don't know what they all add to white PLA but I recommend you choose an uglier color and spray paint it afterwards with an automoble primer and then any spray paint on top of the primer.

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