PA increasing print time ++

pro3d

Oh that seems high but I can try. Also I just figured my E jerk was 600 not 900 as of recommended by dc42 long time ago

deckingman

@pro3d 3600 is what I run and providing your axes "jerk" values are lower, it will ensure that any move will only slow down to the "jerk" speed of you X Y motors, rather than slowing down to the "jerk" speed of your extruder(s). That is the likely cause of the print time being increasing when you apply pressure advance.

Exerqtor

I'm trying to do apply PA myself and i have the same issues, way to slow. And if i put 3600 in E jerk my extruders skip like crazy and it all goes way to ask ( to the point where i can't even lay down the first layer with PET-G since it don't stick). It must be some actual way to get the right values, and not just blindly putting in numbers and hoping it goes ok?

pro3d

@exerqtor

It feels like a guessing game but somewhat qualified. The idea to run E jerk higher than XY jerk sounds like a reasonable theory to avoid slow down due to e jerk and related to XY speeds. How ever I dont see the point of going to 3600 so I put in 1800 as to 600 before to check and it is still slowing down but maybe a little less

deckingman

@pro3d Bear in mind that "jerk" isn't a speed that the extruder has to attain. It's a cut off speed. Direction changes occur when the lowest speed of X Y or E is reached. So setting it high ensures that the speed will be limited by the axes and not the extruder.
Anyway, you asked for advice as to why PA increased print time. I've given you the answer and advice based on results of extensive testing. Set it to whatever you like. Best of luck.

pro3d

@deckingman

Thank you for the advice. I am applying your suggestions but in increments. In theory it should be enough to set the e jerk high enough so it is not the limiting factor, how ever E speed is different from xy speeds and the change of direction can happen much quicker I guess but of course we dont want skipped steps

Thanks for testing this extensively and getting a good setup. What kind of printer/extruder/hotend are your values for?

pro3d

I never got any answer on the upside of using PA vs standard retraction. What is the reason to use PA over Retract?

zapta

@pro3d said in PA increasing print time ++:

What is the reason to use PA over Retract?

Is PA substitution to retract? I would think that retract may still be needed, e.g. when moving between islands.

deckingman

@pro3d Both do different jobs although there is some interaction. A better term for pressure advance would be "pressure compensation". To understand it's effect, you need to understand how and why it works. In a nutshell, under certain conditions, pressure at the nozzle can increase during a print move. So towards the end of a move, the print head stsrts to decelerate and so does the extuder. However, because of the latent pressure that has built up during the move, the rate of extrusion remains higher. This leads to over extrusion at the end of the move. Conversely, at the start of a move, the print head accelerates but it takes time for the incoming filament to melt and get forced out of the nozzle. So the rate of increase in extruded filament lags behind the rate of increase in the print head, resulting in under extrusion at the start of a move. Pressure advance works by increasing the extrusion rate at the start of a move and decreasing it at the end of the move. It therefore follows that at the end of a move, if the pressure at the nozzle is lower when PA is applied, then the filament will be less likely to ooze during subsequent travel moves, and so less retraction may be required.

zapta

@deckingman said in PA increasing print time ++:

if the pressure at the nozzle is lower when PA is applied, then the filament will be less likely to ooze during subsequent travel moves, and so less retraction may be required.

Thanks. I was not aware of this dependency.