Pressure Advance with Large Nozzle/Direct Drive
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Curious if any difference with large vs Small nozzle. on a direct drive in terms of pressure advance settings.
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@Adamfilip extremely (extremely!) likely there will be a pressure advance difference.
Mosquito/BMG setup, I use .087 for .4mm, and .039 for .8mm.
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@Adamfilip Yes. A large nozzle is far less restrictive than a small one so the pressure build up within the hot end/filament input path is far less. Also, with larger nozzles the extruder speed is lower for any given volumetric flow rate, which will reduce any pressure build up in the filament feed path even further. With direct drive and a largish nozzle I'd be surprised if you need any PA at all.
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@deckingman hmm one thing i notice more is that If i do a free-air extrusion. when I watch the plastic coming out. it retracts alot more when it stops and cools vs a small nozzle. like it needs extra restart during retraction perhaps
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@Adamfilip I use bondtech BMG direct extruder with a hot end that has a 1 mm nozzle. I ran a print test and ended up setting PA to 0.06. This thread has the info and a link to photos I took of the printed test pattern. I have found that since turning on pressure advance, the thing tends to over extrude and I have to set the extrusion multiplier to 85% to get normally extruded prints. I set PA to 0.065 based on the results in the photos and it seems about right (once I adjust the extrusion multiplier).
Tuning the retraction is a real problem with 1 mm nozzle. If you print a test part and tweak the retraction just right, you can get a great result. However, if the travel distance changes, it all falls apart. You'll get gaps or blobs at the start of each new line. I suspect there is some math that needs to be applied to retraction based on travel distance/time, nozzle diameter, temperature, print material, and print speed/acceleration. Retraction tuning prints are usually vertical posts paced at various distances, and all I have seen are too small for a 1 mm nozzle. You'll need to create your own test print using larger objects that won't mushroom when printing layer on top of layer.
If you manage to get it all tuned up and working well, post the info on how you managed the tune-up.
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@mrehorstdmd currently im finding my extrusion multipler is at 0.97 - 1.0 with a 0.8nozzle revo and 0.5mm layers. trying to eliminate seam gaps currently.
PLA+
230 Degree, 70 Bed
45mm/sec
1mm retract
0.2mm extra restart -
@Adamfilip The problem I've found with large nozzles is that filament simply oozes out of it's own volition/gravity. You'll notice it mostly when you first heat the hot end. When you start to print, the hot end is partly evacuated and you have to refill it before anything comes out of the nozzle. A skirt will usually fix this but the same thing happens during any non-print moves. The net result is that it appears to over extrude at the end of a move (because filament continues to "ooze") so the temptation is to use more retraction. But then at the start of the next move, the hot end has to be replenished before anything comes out of the nozzle so you get under extrusion at the start of a move. This under extrusion / over extrusion at the start and end of each move is akin to the effect seen when pressure builds up, but for a different reason. I've done a lot of work with nozzles up to 1.5mm fed via multiple extruders and every combination of settings imaginable. The conclusion that I've come to is that large nozzles only work where parts have a minimum of non-print moves - e.g. vase mode.
Also, slicers are not good at generating infill for large nozzle (layer) widths where you have say a solid base abutting a curved perimeter. If the nozzle width is 1mm, they tend to do a very bad job of generating infill that needs to be say 0.5mm or less. So you get gaps.
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@deckingman yes, it needs a little extra restart after retraction to keep it flowing.
almost needs a reverse pressure advance, to increase pressure vs back it off. lol -
@Adamfilip That's not how PA works. It does indeed increase pressure at the start of a move and decrease pressure at the end of a move. It's because with a "normal" hot end, pressure will build up during a move causing over extrusion at the end, but at the start of a move, it takes time for the pressure to build up sufficiently for filament to start flowing from the nozzle. So it's the same effect as filament oozing from a large nozzle but caused by different reasons. PA might help (even though there may not be any pressure build up) because it will advance the extruder at the start of a move and retard it at the end. But as others have observed, the PA value will only be correct for one non-print move length and will be incorrect for other non- print moves. That's because the longer the non-print move, the more filament will ooze out.
