Pressure advance again
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What is the latest test that people run to determine pressure advance? I use an old python script that was in vogue a year or so back but when I am running it now I can't seem to get it right.
I use ver 3.4.0 on a Jubilee and the extruder runs off a tool board. Should I upgrade to the latest firmware ie.: is the problem with pressure advance in 3.4.0 fixed in the latest release?
I must admit, I have not followed the pressure advance saga but I am having all kinds of issues and need to start my tuning from scratch. -
@jens55 I've explained the method that I use many, many times but nobody takes any notice so I'm not going to reiterate it again. But you should know a few things. Firstly that pressure advance isn't perfect, nor will it ever be. Secondly, the very name is misleading because it consists of both pressure advancement and retardation. Thirdly, it isn't a panacea for every print artefact. Forthly that there is an interaction between PA, acceleration, jerk and retraction settings. And I could go on.....
But you need to understand what happens inside a hot end. At the start of a move, the carriage will accelerate up to speed and the molten filament flow needs to match this acceleration. But it usually does not because although the extruder speeds up and incoming filament accerates, it takes time for that filament to melt and then for that molten filament flow from the nozzle to accelerate up to speed. The net result is that there is a rapid build of of pressure but a time lag before that translates to an increase in flow from the nozzle. So you get under extrusion at the start of a move. Conversely, once pressure builds up, it takes time for it to decay. So at the end of a move, the carriage decelerates but the latent pressure that builds up inside the system continues to force filament out if the nozzle at a higher rate than the carriage deceleration. So you get over extrusion at the end of a move. PA attempts to compensate by accelerating the extruder faster at the start of a move and decelerating it faster at the end of a move.
Therefore, it is logical that to tune PA one should use long, fast moves where the affect of this under/over extrusion are more pronounced and where the affect of any PA can be easily observed.
This is all well and good for long(ish) moves but when you start to consider what happens with a series of short moves, things get much more complicated. Taken individually, the moves might be too short for pressure to build up significantly and the extrusion amount might be too small to apply PA to it. But taken cumulatively, there might well be a lack of extrusion at the start of the sequence and too much at the end. So how and where to apply PA becomes much more complicated and is why in my opinion, it will never be perfect.
All in all, the best strategy (again in my opinion) is to take steps to reduce these pressure pulses. I.e, print slower, print as near constant speed as possible, use a bigger nozzle. For example, a 0 5 mm nozzle gives you a more than 50% increase in cross sectional area over a 0.4mm nozzle and helps enormously.
That's my take on it anyway..,.
