How to speed up print with high linear advance.

deckingman

@Turbo Difficult to tell from the pic but it looks like under extrusion in the middle of the moves

@bot said in How to speed up print with high linear advance.:

Which aspect do you disagree with? 2400 is completely unnecessary. There is no scenario, except retraction, that ever requests the extruder to move 40 mm/s during a print.

Extruder Jerk interacts with PA - if you don't believe me, ask DC42. With a Titan or BMG and 400 steps per mm, I can categorically say that if extruder jerk is set to 600, it will slow things down. I haven't just made that up - that's from real use case testing.

bot

@deckingman You must use very high amounts of PA.

Even then, 2400 is way more than is necessary. In what situation, of PA, would the extruder need to instantly reverse by 40 mm/s? None that I can imagine.

deckingman

@bot said in How to speed up print with high linear advance.:

@deckingman You must use very high amounts of PA.

Yes - like the OP. Maybe it's a feature of multi input hot ends because my Bowden tubes are only about 200 mm long - but then I have 5 of them.

deckingman

@bot said in How to speed up print with high linear advance.:

@deckingman You must use very high amounts of PA.

Even then, 2400 is way more than is necessary. In what situation, of PA, would the extruder need to instantly reverse by 40 mm/s? None that I can imagine.

I don't profess to know how the interaction of extruder jerk and PA work - only that there is that interaction.

Turbo

@deckingman What it looks like to me is not enough pressure advance. However, there is no change between 0 PA and 3 PA and everything in between. Kinda lost on why its not making a difference, especially when i can clearly hear the motor upping the pressure advance with each line.

bot

@deckingman it's a very simple interaction if you care to think about it.

A given X/Y feedrate at a specified layer height/extrusion width combo has a nominal E axis movement speed. Typically, this is no greater than 5 mm/s. PA simply applies an advancement or adjustment based on the current instantaneous actual E acceleration happening at the moment. If we imagine that the nominal E speed of the move would be 5 mm/s, and the PA is set such that during acceleration it requires TWICE as much plastic to flow, it will have to jerk to 10 mm/s instantly. If we have our jerk speed set lower than 5 mm/s, it will slow down the XY acceleration of the print move (and therefore the required E acceleration of the print move, because they are coordinated).

bot

What print speeds are you using for calibrating PA? What extrusion width and layer height combo are you using?

deckingman

@Turbo said in How to speed up print with high linear advance.:

@deckingman correct, however it begins to underextrude/not enough material and lines don't connect.

15867946996626117362152457791302.jpg

This is a test with 0-0.5 values. 0.05 stepping. Because 0-2 and 0-1 showed no change, similar to this one. Not the best pic but it wouldn't let me upload a higher quality one.

OK. Taking a gander at that picture, it looks like the lines are fat at both ends but thin in the middle. What normally happens is that at the start of a move, the carriage accelerates but the melt rate of filament lags behind, so you get under extrusion at the start of a move. Then at the end of a move, the carriage decelerates but because pressure has built up, filament continues to get forced out at a faster rate, so you get over extrusion at the end of a move. PA compensates by advancing the extruder at a faster rate at the start of a move and retarding the extruder so that it slows down more at the end of a move. But as I said, your image seems to show that the lines are thin in the middle, which might indicate that you are simply exceeding the melt rate that the extruder is capable of.

Turbo

@bot
From the generated .gcode

Created: Mon Apr 13 2020 09:13:37 GMT-0700 (Pacific Daylight Time)
;
; Settings Printer:
; Filament Diameter = 1.75 mm
; Nozzle Diameter = 0.4 mm
; Nozzle Temperature = 210 °C
; Bed Temperature = 60 °C
; Retraction Distance = 2.6 mm
; Layer Height = 0.2 mm
; Z-axis Offset = 0 mm
;
; Settings Print Bed:
; Bed Shape = Rect
; Bed Size X = 305 mm
; Bed Size Y = 188 mm
; Origin Bed Center = false
;
; Settings Speed:
; Slow Printing Speed = 1200 mm/min
; Fast Printing Speed = 4200 mm/min
; Movement Speed = 7200 mm/min
; Retract Speed = 1800 mm/min
; Printing Acceleration = 2400 mm/s^2
; Jerk X-axis =  firmware default
; Jerk Y-axis =  firmware default
; Jerk Z-axis =  firmware default
; Jerk Extruder =  firmware default
;
; Settings Pattern:
; Linear Advance Version = 1.5
; Starting Value Factor = 0
; Ending Value Factor = 0.5
; Factor Stepping = 0.05
; Test Line Spacing = 5 mm
; Test Line Length Slow = 20 mm
; Test Line Length Fast = 40 mm
; Print Pattern = Standard
; Print Frame = false
; Number Lines = true
; Print Size X = 98 mm
; Print Size Y = 75 mm
; Print Rotation = 0 degree
;
; Settings Advance:
; Nozzle / Line Ratio = 1.2
; Bed leveling = G29 ; Level bed
; Use FWRETRACT = false
; Extrusion Multiplier = 0.97
; Prime Nozzle = true
; Prime Extrusion Multiplier = 2.5
; Prime Speed = 1800
; Dwell Time = 2 s
;
; prepare printing

deckingman

@bot said in How to speed up print with high linear advance.:

@deckingman it's a very simple interaction if you care to think about it.

A given X/Y feedrate at a specified layer height/extrusion width combo has a nominal E axis movement speed. Typically, this is no greater than 5 mm/s. PA simply applies an advancement or adjustment based on the current instantaneous actual E acceleration happening at the moment. If we imagine that the nominal E speed of the move would be 5 mm/s, and the PA is set such that during acceleration it requires TWICE as much plastic to flow, it will have to jerk to 10 mm/s instantly. If we have our jerk speed set lower than 5 mm/s, it will slow down the XY acceleration of the print move (and therefore the required E acceleration of the print move, because they are coordinated).

...........and segmented moves such as circles where PA is no applied to each segment but at the end of a curve?

But I don't want to continue this because I have my real life experience of empirical testing and what happens in fact, which you don't believe. Therefore, you must think that I am just making this all up for some unknown reason, or that I am a liar. Either way, there is no point in my continuing.

bot

@deckingman at this point, I don't know what you're even talking about.

But, why would PA only be applied at the end of a curve of a circle? PA is applied any time there is extruder acceleration.

bot

@Turbo is your Titan extruder set up in direct drive?

One thing to check before you go on is that your extruder idler gear is sufficiently applying pressure to the filament against the hobbed gear. I have had problems in the past where fast extruder moves were lost because the filament slipped on the hobbed gear. Get a flashlight and watch the filament go through the gears if you can, and ensure it's moving. I saw my filament slipping and had to remove a spring from the idler and screw it at a fixed distance.

Turbo

@bot 600mm Bowden config. No slipping.

bot

Ok, good. Another thing to check is that your bowden couplings are tight and have no free play. You could lose the PA adjustment to the freeplay.

Turbo

@bot nice and toight. no mechanical faults.

deckingman

@bot

https://duet3d.dozuki.com/Wiki/Pressure_advance

Penultimate paragraph - Quote

"When the extruder acceleration changes, the extruder velocity has to change instantaneously. If the configured extruder jerk is too low to permit this, the extruder acceleration will be restricted so as to honour the maximum configured extruder jerk, and this may in turn limit the printing acceleration. So if enabling pressure advance slows down printing, this may be a sign that the allowed extruder jerk configured in the M566 command is too low. This may prove problematic for remote direct drive extruders like the Zesty Nimble which use a high gear ratio and low jerk values."

bot

@deckingman thanks. Did I ever say anything that contradicts that stament? Sorry if I did!

bot

@Turbo if you can rule out all mechanical issues, that's good!

I'm looking at your PA script, and the X/Y (not e) jerk values you seem to be using. I'm wondering if the jerk value being higher than the commanded feedrate of the small move is disallowing PA to take as much effect as it could. I've been playing around with PA and accel/jerk a lot lately, and noticed some time ago that you NEED to have an acceleration phase in the X/Y movement for PA to take any effect. Without acceleration, there is no PA applied. Try lowering your XY jerk rate, try 15 mm/s (900 mm/min) and see if you can notice more of an effect from PA.

Turbo

@bot No dice mate.

bot

Are you ensuring that the test script is actually sending the proper command to the correct drive number? Is the extruder you are using actually D1?

Clearly I'm running out of ideas. It seems you were previously noticing results of PA, so something has changed since you adjusted your settings.