Can 'pressure advance' cause negative filament feed ?
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I am printing something tiny. I am down to a 0.2 mm nozzle, 0.08 mm layer height and the features are less than 1 mm squared. and decreasing in size. I have a pressure advance of 0.4 set because of a very long bowden tube.
The model prints fine before it gets to the tiny features but once it hits those features, the aggregate filament feed is actually negative.
I am aware that pressure advance can cause a negative feed at the end of a section (and see it quite often). I was however under the assumption that given let's say a straight line run where the printer was extruding, the net feed (between initial extra feed and the reduction or reversal of feed at the end) would always be a positive amount.
Looking at the g code file, the extruder is only advancing. Looking at the extruder feed gear, the extruder gear is actually going backwards a bit.
As I said, this only happens when there is a long string of very tiny features that each require a tiny bit of material. I am pretty much at the limits of resolution on my extruder stepper motor with the steps being so tiny.
Retraction is disabled and I can't think of anything else that would cause negative feed.Thoughts ?
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@jens55 Yes that's normal. At the beginning a move, pressure advance will cause the extruder to accelerate faster than it would otherwise do, so one doesn't tend to notice this. At the end of move, the extruder will decelerate faster than it would otherwise do - even to the point where it passes 0 speed, so it can run backwards. The net extrusion amount for the move will be the same as if no pressure adavnce was being employed, it's just that you get more at the start and less at the end. Things do work slightly differently when you have a series of small segmented moves such as arcs or circles because each move is too small for pressure to be build up but there would be a cumulative effect when several small segments are printed. DC42 will tell you exactly how that works.
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I am aware of the faster feed at the beginning and slower feed (or even reverse feed) at the end. What I was trying to figure out was if the overall feed (total amount fed during an entire feed sequence) could actually be negative. When I say 'total amount' I mean the faster feed at the start plus the main section of feed plus the reduced (or possibly negative) feed at the end. -
hmmmm, not sure if the upload worked so I am re-doing it
The gcode:
0_1566272710536_CFFFP_reduced hirth.gcodethe .3mf file: ..... I had to stick on a .txt in order for the system to accept the .3mf file
[0_1566272789447_CFFFP_reduced hirth.3mf](Uploading 100%) 0_1566272850068_CFFFP_reduced hirth.3mf.txt -
Cura appears to be doing some awful things to the teeth. I would suggest trying to slice it in Prusa Slicer for a sanity check.
Also, I don't think that .3mf worked quite right. It's still just the sliced gcode.
I may have misled you by saying Export. To get the proper 3mf simply go to File, Save in Cura to produce a .3mf archive of the entire platter including STL, printer settings, and print settings.
And yes you'll have to change the extension to post it to the forum.