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DaveOB

Cura not retracting

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Cura 3.2.0 question - can Cura force retraction when Combing mode is On ?
Printing a hollow cylinder that has 1 inner perimeter, 1 outer perimeter, and 1 infill line between.
If I enable Combing then I get a near perfect print, but some scars ( missing extrusion ) on the outer perimeter on some layers.
Retraction is set for Z layer change.
After seriously increasing the ' Retraction Extra Prime Amount ' I have found that the Extra Prime occurs after the layer change at the start of the inner perimeter, but there is no retraction ( and Extra Prime ) when moving from the end of the inner perimeter, to the start point of the outer perimeter.
It appears that retraction is not happening unless the nozzle passes the perimeter ( which it does not do because of combing ) or when the layer changes ( which it does ).

So the question is, if using Combing and ' Z seam alignment ' is Random, how do I force retraction Extra Prime to couteract the effect of ooze while moving to the start of the outer perimeter ?

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Update : 100% quality improvement - after playing with settings for my 0.8 nozzle ( and still getting blobs, scars or both ), I decided to write the custom script, so Cura slices w\ith no retraction, and the post slicing script manually adds the retraction.

my logic is that, especially with the combing, the nozzle is mostly moving over an existed printed surface, which draws out the ooze from the nozzle.
So what I did, was calculate the distance between the retraction and the reprime, and adjust the reprime value relative to the distance.
My retraction is 0.5mm
the minimum reprime is 0.6mm ( so 0.1mm more than the retraction )
if distance is less than 4mm, then reprime only 0.5
any distance travelled between 4 and 40mm is reprimed proportionately between 0.6 and 1mm
Results on the 3 prints that I did today have been very positive.


it would appear, at initial glance, that the layer smoothness is also greatly improved, and I think this is related to the pressure in the heat block. If the retract is set at a single value, and there is some ooze on longer travels, then the pressure in the block will reduce, and the scar occurs.
On short moves, the single reprime value is too moch, causing a blog.
With a variable reprime value ( based on distance travelled ) the pressure in the block is more consistant.


Maybe this is something that the Cura developers could consider adding as a feature ?

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