Pressure Advance Calibration

[wilriker]

Thanks to everyone, I decided to put it in the filament's config.

[deckingman]

@token47 said in Pressure Advance Calibration:

It will vary a lot for different materials (i.e. PLA vs ABS) and may vary between different brands of the same materials even. I consider the value valid for the specific filment the test was made on and created macros to change the value when changing the filament.

Thinking about the mechanisms at work which cause pressure to build up, it's likely to depend on the viscosity of the filament if everything else (Bowden tube length, melt chamber size and nozzle diameter) remain the same. In my own experiments, I've found that print temperature can have a small effect as it changes the viscosity but I can't say that I've noticed any difference between brands of the same filament. In fact, I can't say that I've notice any difference between PETG at 220 and PLA at 195. Maybe the difference in temperature cancels out the different viscosity characteristics of the materials. I can't print ABS so cannot say if that behaves differently.

[wilriker]

This is not completely on-topic but still fits here I hope:
Linear Advance and Non-Linear Extrusion. Are they mutual exclusive or can they be used complementary? If the latter what would need to be tuned first?

[dc42]

@wilriker said in Pressure Advance Calibration:

This is not completely on-topic but still fits here I hope:
Linear Advance and Non-Linear Extrusion. Are they mutual exclusive or can they be used complementary? If the latter what would need to be tuned first?

They can both be used together. I don't think they should interact much, but if in doubt I suggest you tune nonlinear extrusion first.

[OBELIKS]

What the? Even at S0.996 I am still seeing a step between the slow and fast part. Why?

[wilriker]

@obeliks What kind of extruder are you using? The Bowden setup of the P3sTE Mk2? AFAIK Bowden setups use larger PA values - and my original Anet MK8 direct extruder even needs 0.144 apparently.

[OBELIKS]

I know, but this is a bit silly.
I am using a cloned Titan extruder. A bad clone.
But still, long bowdens are supposed to have around 0.2, and I have a 40cm long bowden

[deckingman]

@obeliks I haven't looked at the file but I'd have thought with that test, that acceleration and instantaneous speed change (jerk) will play a big part in the results. Forget the 100mm/sec speed unless you have a genuine E3D volcano - even then, you might struggle depending on nozzle size and layer height.

Maybe your clone just has a very low melt rate or maybe it's got a partial blockage or the filament is bulging in the heat break area causing a restriction. Suggest you try something like a test cube without any pressure advance, just to check what speed you can print at (i.e how fast can melt filament). If the melt rate equates to (say) 60mm/sec or less, then trying to print at 100mm/sec ain't gonna work - no matter what you do with pressure advance.

[wilriker]

@deckingman At least with my rather low print acceleration it never got faster than 83.3mm/s (I need to tune this some day) but a simple calculation of 0.4mm extrusion width, 0.2mm layer height (as generated by the script) and 100mm/s print speed this would add up to 8mm³ of filament. IIRC a V6 is able to melt about 9-10mm³/s so this should be possible at least in theory (not taking into account any counter-pressure created by not extruding into thin air but "against" a surface).

[Phaedrux]

@deckingman said in Pressure Advance Calibration:

I'd have thought with that test, that acceleration and instantaneous speed change (jerk) will play a big part in the results.

I've noticed the same. Jerk especially seems to have a effect. The higher the jerk value, the lower the pressure advance value I need.

In the back of my mind I've had an idea for a systematic tuning guide. What parameters to start with, and what order to proceed in, with example test models to use for consistency. Printer tuning can seem like a dark art, but really it's just a complex interactive system which so far has lacked a rigorous systematic approach to testing and verifying results. You've done more than most in experimenting and codifying the way the system interacts on your blog.

[deckingman]

@phaedrux Yes I think it's best to tune everything else first - speeds, temperatures, acceleration, jerk etc until you get the best quality you can. Only then start playing around with pressure advance and other things. And only ever change one thing at a time (I'm not a fan of Taguchi methods). There are just too many interactions going on I've found. Oh, and make copious notes along the way.

[bartolomeus]

For python noobs like me: I uploaded the script into a browser based python implementaition, and it outputs the gcode: http://www.skulpt.org/#

[bartolomeus]

I just printed with this script two times, one with PA from 0 to 0.2, and one with PA from 0.1 to 0.3.
During the print I entered M572 a few times to see what the actual settings are, and I could see the values change. At the end of the second print the returned value was: M572 - Extruder pressure advance: 0.298, 0.000

First: what is the second output: 0.000?
Second: I saw nothing in the print....really nothing. No gaps tearing or anything.

My setup: CoreXY, E3d, Bondtech BMG, 650mm capricorn, Firmware 2.02RC1

[wilriker]

@bartolomeus It is not gaps or tearing that you are looking for but the value where there is a consistent extrusion width.

[bartolomeus]

@wilriker ok, but I still see nothing. All layers are identical, al columns in the print turned out exactly the same. Nothing like the pictures above.

[Phaedrux]

@bartolomeus 650mm Bowden tube is long. Perhaps even higher values are needed.

The second value reported as zero may be from a second extruder that's defined but unused?

[wilriker]

@bartolomeus That is interesting. My latest test can be seen here.

Regarding the second value: this is the one for the second extruder. If you did not explicitly tell RRF that there is only one (don't remember the exact command, it's the one where you assign motors to axes) then I guess it has the second extruder configured by default.

[bartolomeus]

@phaedrux higher than 0.3? I went through my config to be sure, but there's no second extruder configured. I'll go over it again and then post my config.

[bartolomeus]

[wilriker]

@bartolomeus So you definitely need higher values. All layers are identical but all are identically bad. In my image at about a little above the middle layer that is how it should look like. One consistent extrusion width from left to right. No bumps.