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Under extrusion when printing with PLA and PVA

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Hi,

I have problems printing PLA together with PVA. Espesially I failed two times printing the following model:

https://www.thingiverse.com/thing:1979068

At a sertan hight it comes to under extrusion of PLA.

The first print already freed from PVA with water was printed with default settings in Cura 3.0.4 for a layer height of 0.2mm. For the second print I raised the temperature for PLA from 205°C to 220°C.

I still think it is a temperature problem because especially on the second print you can see unattached PLA at one side of the print. So I think that there is still a high pressure in the nozzle when it heads up again so the material comes out ... but too late. That material should have been on the last part of the previous layer.

I think it may have to do with the switching between both hot ends when the active one begins to cool down and the inactive one heads up.

Do I need to adjust the standby or final printing temperature for PLA? Does the printer cool down the nozzle for PLA too early?l

I also appended another picture with two ultimaker bots. The right one was printed with only PLA. The left one was printed with PLA and PVA with the robot lieing on its back. As you can see the walls of the left one have a bad quality. Maybe the reason is the same the more difficult print fails.

20171123_080127.thumb.jpg.f631b9cdf9b3021842e0c9e84bf51a33.jpg

20171123_080055.thumb.jpg.294f89a33c4d03e40822fc36f4833819.jpg

20171123_080102.thumb.jpg.3848da7c75b002341bcc734d06584803.jpg

20171123_080116.thumb.jpg.29cfc70350f10c30613fe0c35c0ecd03.jpg

20171123_080158.thumb.jpg.1d13a063a177a9a6676bf8564e2c8f56.jpg

20171123_080800.thumb.jpg.aee560b0e9ed1a790ac97d4d16a54082.jpg

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What you mean by cold and hot pulls?

The problem occurs during the print at a certain height.

That could be because the humidity in the filament causes it to clog a bit during its heating cycles.

However, check this out to introduce yourself to the hot and cold pulls to clean out the PVA.

When dealing with PVA, moisture in the filament is just the first go to response in almost every situation. Cleaning out the nozzle will rule this out.

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That is weird. I do not believe I have ever heard of that. I know I have never seen it on my printer.

Wanna try something out of the ordinary? Try switching the cores to the opposite slots and feed the materials through again to match the cores. Then, reslice so that the printer can identify which core is where properly, and see if it does it again.

I know it sounds weird, but maybe give it a try.

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