Linear advance, what to look for
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@dc42 yes i will see to that in a few minutes, gonna walk the dogs first though
Hope i can do it on mobile version..
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Ehm.. how do i post pictures? I dont have an url link for it... if it is the directory on my phones storage, then i dont know that either..
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@deckingman Did you mean non-linear extrusion? Linear advance is Marlin's version of pressure advance. I'm a novice with the duet and want to make sure I'm not missing something.
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there is an upload file button during the reply. on android pictures are in the dcim folder
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Im having huge layer inconsistensies... im used to the smooth and even layer lines as on the backside..
But its very uneven in the layers.. this happens on all prints, with 98% of my pla... this seems to become more prominent the higher i go in temperature..I have been messing with this retraction stuff for days, but when k got dialed kn retraction, layers started to go bad... hoped this PA could fix it...
Batch 1..
Cube 1
! 
Cube 2
This is batch 2...
Cube 1
Cube 2
Batch 1 is ranging from 0.1 to 0.3..
Batch 2 is made with higher values, ranging from 0.6 to 0.8, so i expect that to be worse....
but the difference in both of them are crazy.. same gcode and everything just different values..
these are printed diagonally on the bed, with about 150mm spacing between, just to see how retraction performs on long travel retracts.. so dont mind the small blobs from that... can be removed by poking to themAnd i dont know what to adjust, i wont adjust settings without any thought, cause suddenly everything goes haywire and i have to start all over from scratch and waste several kg of filament for everything
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@jamesm said in Linear advance, what to look for:
@deckingman Did you mean non-linear extrusion? Linear advance is Marlin's version of pressure advance. I'm a novice with the duet and want to make sure I'm not missing something.
Yes I did - I wasn't aware that Marline referred to Pressure Advance as Linear Advance so I assumed you meant non-linear extrusion which was what all my waffle was aimed at -
ignore it all.To post picture, look at the buttons across the top when you compose a post - to upload a picture is the middle button - looks a bit like a boulder falling down a mountain.
Ref pressure advance. What happens in a hot end is this. As you push filament into a hot end, pressure can build up, mostly because you are trying to push the molten filament through a small orifice, and because it takes time for the solid filament to melt. Obviously this doesn't happen if you print really slowly but the faster you print and the longer an extrusion move, then the more pressure can build up. When you do a print move, the carriage responds almost instantly to the changes in acceleration at the start and end of the move but the filament does not. There is a lag at the start of the move because the filament is viscous and acts like a sponge, hence an initial pressure build up without much change in the amount of filament coming out of the nozzle. So the carriage accelerates up to speed but the rate of change of flow rate for the extruded filament is much slower resulting in under extrusion at the start of the move. At the end of the move, the opposite happens. That is to say, the carriage decelerates but because of the latent pressure that has built up inside the hot end, the filament is still being forced out at a relatively high rate despite the fact that the extruder is slowing down. It therefore follows that this leads to over extrusion at the end of a move.
It therefore also follows that the longer the move, and the faster a move the more pressure will build up. So what works well for me is to print a large cuboid with 100% infill and observe the start and end of each line to look for under or over extrusion. Then I change pressure advanec "on the fly" until I can detect no difference in the extrusion between the start, end and middle of the bead that is being laid down. Once this value has been obtained, I find that it works well for all speeds. BUT, anything that can change the viscosity of the filament will affect the pressure compensation requirement. So that's the filament itself, as well as the print temperature. I haven't found any need to change the PA value for different reels of filament - one value seems to work well for all PLA although a different value is needed for PETG.
There is also a strong interaction between instantaneous speed change setting (jerk) and pressure advance. Essentially, more pressure advance compensation is needed for lower "jerk" settings and vice versa". With a high jerk setting, the carriage velocity starts and ends at a higher value so the acceleration and deceleration phases are shorter.
HTH
Edit. I was typing all the above waffle before I saw your pictures. PA isn't going to fix that. Disable it for now until you get everything else dialled. I'd say in general that because of the gas between layers and lines, you have some under extrusion issues.
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@deckingman
Yeah i figured it out, you couæd slide the topbar to the side... this design just looked so oldschool that it didnt cross my mindWell looks like it should be so much of a hassle then...
See my pics, specially with the top and bottom, since i cant get the perfectly evenly look you mention, which i would LOVE to have..
But my main focus were the layer lines though...
But if the top is supposed to be better, i have absolutely no idea what is going on.. since the walls go completely bad above the 0.3 margin... -
Under extrusion happens due to the pa... if i turn if off it both under and overextrudes.... tried 3 different all new hotends, rqnging temps from 190 to 260c with pla... yes 260c!!!! And it can print with that, but doesnt fix this...
I saw no difference at all from 90 or 100 percent flowrate, so i do t need to get my bondtech dialed in... it has always worked perfectly...
I have always had perfect looking layer lines on this printer... but i cant get it now... at all.. in any way...
And it happend along the way lf my dialing in retraction on new, with the new heaterblocks... wasted over 2kg of filament of freaking bemchies man... i hate this pile of shet
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I read everywhere that pa shoukd make blobs at retracts go away and make nice even layers...
Which is exactly what im doing this for...
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If i disable PA, i have to battle the same issues still, including retraction too... definately pa gives me perfect retracts
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I hqve now switched over to some of my more trusted pla...
Does much better now... looks almost perfect as what i can see..
But the extruder is "jerking" like mad... is that a good or bad thing?
Pa is currebtly at 0.15 -
@johnjohn1990 Lots of posts, lots of questions, lots of everything..........
I think you should take a step back and try not to change too many things. As I said before, pressure advance isn't the answer. You need to get everything else dialed in first. Print nice and slow. What speed are you using? What layer height? If you print slow (say 40mm/sec), then you are unlikely to get a pressure build up so you are unlikely to need to compensate for it. Likewise retraction. It's only applied at the end of moves to prevent blobs forming due to the filament oozing during non-print moves. It won't have any effect on the gaps you are seeing.
Have you done all the basic stuff? Have you got your steps per calibrated - especially the extruder. Have got the correct values for your thermistor? Have you tuned the heater?
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@johnjohn1990 I can't keep up with all your posts. I don't know what question I'm trying to answer. Disable PA for now - it;s most likely masking something more fundamental which is what you need to fix first.
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What do you want to know from.before i turned pa on?
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I had blobs at both start and stop, no matter what i did... 15 or 45mm/s and or 0mm or 7mm retract didnt matter...
If it didnt blob, it just stringed instead..But it generally keeps overextruding the first 20mm or so of a startpoint, after a retract, which makes awfull looking layers..
If i went too fast or too high in retraction, it underextrudes instead of overextrudes... there is no golden midpoint!
Though the best one i have found is 40mm/s retract and 20mm/s prime speed.. im using cura.. been using the same profile for over a year, on all printers ive ever had in my hands since i made this profile...
Always worked perfect..
This feels exactly like if it were an e3d all metal hotend that used too much and too fast retracts.. but its not... its an olsson block.. -
@johnjohn1990 I suspect that in the time it takes me to type this, you'll have posted twice more.
From what I can gather, you used to be able to print OK, but now you are having problems - yes? If that is the case, then what changed?
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@johnjohn1990 In your first photo showing the Z side of the cube I see a different problem- the infill lines are laying down in pairs with gaps between them. They should all be evenly spaced/touching, suggesting that there's some backlash in the XY motion.
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@deckingman said in Linear advance, what to look for:
@johnjohn1990 I suspect that in the time it takes me to type this, you'll have posted twice more.
From what I can gather, you used to be able to print OK, but now you are having problems - yes? If that is the case, then what changed?
Yes... i had a clog, and had to clean out my heaterblock and nozzle.. when i reassembled it again, it just wouldnt print nicely..
It then clogged again after about 20 prints...
Then i changed out all of the hotend parts twice, with 15-20 prints in between, all with the same results..If retracts looked good, layers were inconsistent, just as it is with the bad PA settings... and if i got layers to look good, retracts either blobbed or stringed, or had to be printed at temps i can print abs at which made the nozzles clog over and over... abs prints perfect btw, absolutely perfect..
Yes i did change out parts.. but the fact that it still were there, with the same parts it previously has been printing with, and have had issues ever since, is so strange to me...
PA fixes my retracts... right now it actually look extremely good... i am on the edge of saying that it has never delivered such a quality as this... but the print is only half done, so i wont judge that untill im sure...
Sorry if i tend to just throw a lot of replys.... its not my meaning to confuse...
Ive been chasing my tail for 3 days now, havent hardly slept cause ive used all nights on trying to solve this...
Then finally PA makes my retractions work perfect.. and seemingly also the layers, i just have to only use my trusted pla, for some reason.........
But damn.. it looks awesome so far! Maybe i should try disabling it and just see what happens, just to make myself feel even more dumb lol.. -
@mrehorstdmd said in Linear advance, what to look for:
@johnjohn1990 In your first photo showing the Z side of the cube I see a different problem- the infill lines are laying down in pairs with gaps between them. They should all be evenly spaced/touching, suggesting that there's some backlash in the XY motion.
Its an ultimaker, so yes there will always be a bit of backlash... but maybe it has gone out of allignment when i had to clean the hotend... i will check that when this print is done
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Just to be informative here...
Grey one is when it started messin up...
Green one is currently printing... looks good to me, buuut... time will tell
