Why is retraction distance set to 6.5mm in Cura 2.3.1

[medicalmodeller 5]

I am trying to understand the new version of Cura as I now have an Ultimaker 3. In particular the default profile has a retraction distance of 6.5mm. However when I hover over the info icon it says that this is an absolute value and the calculated value is 2mm.

When I did a print with 6.5mm retraction, the print failed due to the filament getting ground down. The print succeeded when I had 2mm retraction

Thanks

[conny_g 251]

My experience is that this depends on the material. With PLA the retraction is less critical as it doesn't ooze to much. There 4mm is enough. With nGen I need more than 5mm to get the retraction to help and reduce stringing.

For some materials more than 4mm is just not possible because the material is too soft and grinds in the feeder if you have more than 4mm or the retraction speed to high, Glowfill for example. Then you need to fight oozing with lower temperature and lower speed.

What material did you you use?

[medicalmodeller 5]

Thanks

I am using PLA + PVA for the support. I printed a model of a bone so it is complex internally. On my U2 I found that prints failed until I reduced the retraction.

The first print ever with the U3 failed 1/3 of the way through. I found the PLA filament ground most of the way through. I reset the retraction distance to 2 and the bone printed nicely - although it took 13 hours compared with 3 hours on the U2!

Thanks you advice

MM

[Zwakie 21]

I found the PLA filament ground most of the way through.

Did you check you extrusion? If you're over-extruding, the previous layer might be slightly thicker than what the software had planned, making the nozzle to drag over the previous layer.

[Kin 3]

In principle I believe the distance should not affect things. Have you tried reducing the speed and (perhaps more importantly) the acceleration at which you retract? However, because 6.5mm shouldn't be impossible, I wonder if the tension isn't set well for the material.

[neotko 1,417]

On um3. If you observe the material on the top of the cores where they have a gab, and you see what happens when it retracts 2mm you will see that it doesn't move. Because that 2mm are just to release the pressure from the filament onto the cores. So from 2mm to X you actually move filament. I been doing tests with my workingprogress 1.75 cores and I can retract 3mm and actually move filament and stop dripping. But if you change the retraction value, remember to compensate the toolchange retraction distance or you will have increased the chances of dripping while changing tools.

So, just a note. If you change one, remember to adjust the other.