Posts made by nyt

Any ideas on this?

First, it seems baby step is not carrying over between prints. If I have to lower nozzle height by 0.1 for a print, then print again, I have to lower it by another 0.1

Second, it seems the Z height will not move below 0 - $babystep.
For example babystep is at -0.7, G1 Z0 will bring it down to 0.7. running G1 Z0.5 will have no effect.

I use the black matte printbite with an ir sensor I got off ebay. It's quite consistent when doing mesh leveling, but sometimes homing is a bit off compared to the leveling.

https://www.ebay.com/itm/Mini-IR-Differential-Height-Sensing-Board-with-1-Cable-3D-Printer/152929325455

And here you can see the center point, which is the same as the homing probe point, is off by 0.03mm

@dc42:

PS - @DougJones, please can you try the version at https://www.dropbox.com/s/iq9pzfaugyfei7x/Duet2CombinedFirmware-even.bin?dl=0. This is an experimental build that tries to maintain regular step pulse interval at high speeds, so it may play better with servo drivers. The maximum step rate is reduced by about one third.

Any thoughts re: the inconsistent homing mentioned earlier? Using a mini ir-probe with tight tolerances specified, but it's often off quite a bit from the leveling measurements which are always consistent.

I'm getting inconsistent homing still…. Homing at the same point as a leveling point.

This is with mini IR sensor. Using 0.005 tolerance.

M558 P1 X0 Y0 Z1 F180 H0.5 T18000 A5 S0.005

from homeall, which is called before bed leveling...

G1 X198 Y192 F12000
G30

The point highlighted here is the homing point

@garyd9:

Recent code changes have changed z-probe "multi-tap" to use an average instead of aborting when none of the taps are within a specified tolerance. Is there a parameter to get the old (aborting) behavior?

The reason I'm asking is that I had a bltouch (since returned) that would trigger at seemingly random places in a range of almost .2mm. When that happens, I don't trust even an average and would prefer that the entire operation be aborted.

It doesn't just use an average. If two parameters are outside of the specified value, it keeps probing until they're within tolerance. I'm using 0.005 with the IR sensor.

@burtoogle:

What settings are you using for this? I've been cranking up the temperature to reduce pressure and slipping.

For a v6 with 0.4mm nozzle, bowden, titan, 1.75mm PLA @ 200deg I am using M592 D0 A0.010 B0

This gives me reasonably linear extrusion between 1mm/S and 5mm/S extrusion rate.

Thanks, will experiment with this a bit once my print finishes. Currently pushing around 14mm/s at with 0.6mm nozzle 0.4 layer heights at 100mm/s speeds. Hopefully this is the solution along with pressure advance.

@burtoogle:

I can't contribute to the main topic of this thread as I do not use pressure advance, however…

The faster lines are smaller than the slow ones - as far as i can judge. This would be normal when the speed difference would be higher and could be compensated by M592.

I am using M592 and can verify that (for a v6 with 0.4mm nozzle, PLA), it makes a real difference. Before, I was seeing between 5 and 10% underextrusion at higher print speeds. So if you are not using M592 and have calibrated your extruder at a low extrusion rate, it's almost guaranteed that it will be underextruding at higher extrusion rates.

Edit: I forgot to mention that I am using a Titan extruder.

What settings are you using for this? I've been cranking up the temperature to reduce pressure and slipping.

@vp:

it is just my opinion, but i think you missed the point. "missing steps" doesn´t mean only that your stepper misses some steps, it also can mean that the filament slips too much at the extruder gear. When your extruder is pushing hard, the additional E-Jerk introduced by pressure advance can easily overcome the maximum force the extruder gear can handle.

It's not slipping at these speeds. This isn't even fast. IIRC, it behaved pretty much the same even when doubling the layer height. I'll test this more at some point, but I have a long print running currently.

@vp:

Volcano hot ends require more pressure advance as there's a longer melt zone.

No, only at very low extrusion rates and the difference is not that big to e.g. a e3d v6. If somebody uses a volcano, then normally not to operate in the low extrusion rate area. If a volcano would provide more back pressure at higher extrusion rates, nobody would use it…..

so you're confirming what I said. There's a difference between lower and higher speeds.

@vp:

That was PLA printed at 245C. That's pushing it already. The thermistor has been validated accurate as well by external probes, and the tests provided are on two entirely different hot ends/extruders.

In the last appr. half year i have tested > 100 (that is no joke) combinations of nozzles, extruders, and filaments. If you print PLA with 245 °C with a 0.4 at 75/30 mm/s and you see that big difference using a volcano nozzle, your nozzle is really given an extraordinary big amount of back pressure.

Yes, it's a nuisance. It would be less of one if I was using a brass nozzle, but that doesn't work so great with abrasives as we all know.

@vp:

Extrusion is consistent between inner and outer layers.

The faster lines are smaller than the slow ones - as far as i can judge. This would be normal when the speed difference would be higher and could be compensated by M592.

The tip of the nozzle going over the lines and the lighting skews this. The lines are the same width when printed separately as measured by calipers.

@vp:

you're just guessing here, and again, that's not accurate. At least not for the Olsson model.

That is correct, i don´t really know it, but you will find discussions on youtube and on the web about this issue. The data you have provided shows clearly, that you have a lot of back pressure even at low extrusion rates.

The issue isn't all about massive back pressure. It's a large melt zone, and when heated, filament expands as it has a moisture content.

EDIT: after reading other posts about nonlinear extrusion, that looks like the issue. Going to plot out a graph with my setup in a few hours when this print is done.

Speed override would be great, could do a normal home like that, then whatever multi tap command.

@dc42:

@nyt:

the new linear advance in marlin is interesting, as its based on length of filament compressed.

Marlin linear advance is the same algorithm that RepRapFirmware uses; but Marlin implemented it 2 yards later, and the Marlin implementation makes some approximations because it doesn't do precise acceleration.

Did you see the new v1.5 code? They just changed it up

https://github.com/Sebastianv650/Marlin/commits/LIN_ADV_v1.5_final_1.1.x

@dc42:

Yes, that's a known issue.

So how about double tap homing on G30? Possible to add behavior to match bed leveling?

guess ill setup a build environment and start messing with it. if i get any positive results ill submit a pull request.

the new linear advance in marlin is interesting, as its based on length of filament compressed.

@vp:

just my opinion:

1. At 0.4 mm nozzle width, 30 and 75 mm/s at 0.2 mm layer height is "no speed" for a volcano, 0.6 at 20 and 60 mm/s also not, the pressure build up difference should not be that impressive (only if you print e.g. PETG at 200 °C….) - at which temperature and with which filament did you try ?

Volcano hot ends require more pressure advance as there's a longer melt zone.

@vp:

In which direction did the print head move on the 20/60 mm/s picture ?

counter clockwise

@vp:

2. For me it looks like "skipping steps/increased filament slippage" because of too high E jerk when accelerating. What happens if you lower the E jerk (besides that it might slow down your print speed) ? What kind of extruder do you use ?

no steps are being skipped. These are 1.7a motors with titan extruders. No signs of skipped steps anywhere, even at much higher speeds and flow rates.

@vp:

Adjusting the pressure advance settings with speed is in my opinion the wrong way, it doesn´t solve the root problem. The root problem is very likely filament slippage caused by too high jerk/acceleration when accelerating.

This is just not correct. The same trouble is visible with minimal jerk and acceleration.

@vp:

3. Try to increase the temperature and test again to see if the pressure build up is really that important. At higher temperature the viscosity will go down and by that the viscose speed related damping effect will be smaller. In other works, E jerk has a better chance to work…. or tighten your extruder gear if possible, but over tighten it and deforming the filament too much will show the opposite effect.

That was PLA printed at 245C. That's pushing it already. The thermistor has been validated accurate as well by external probes, and the tests provided are on two entirely different hot ends/extruders.

@vp:

5. The inner (fast) lines are not as wide as the outer (slow) ones. Before you start to use pressure advance, you should correct the extrusion multiplier according to extrusion rate using M952. M952 will increase the extrusion rate even more when "jerking" with pressure advance and by that probably not help your problem, but at least the fast and slow straight parts are OK. But maybe it helps, because M952 compensates the extrusion rate correlated slippage as far as it is not too high.

Extrusion is consistent between inner and outer layers.

@vp:

6. A Ruby nozzle might not be a good reference. Afaik it has no real chamfer at the inner side of he tip and by that gives unnecessary pressure build up and maybe other fancy behavior. But for sure it you want to use it, you want to optimize it. But what you found out is maybe not that much relevant for other nozzles - but this could be clarified easily by testing other nozzles.

you're just guessing here, and again, that's not accurate. At least not for the Olsson model.

@vp:

I am used to print at high speeds/accelerations/jerks and and pressure advance has no value for me, because if you use high accelerations (> 1g) there are anyhow no bleeding edges and i would have to lower the E-jerk to get pressure advance working - and by that i would not print fast anymore - so i don´t use it. But i did try to improve retracts with pressure advance (but it doesn´t help).

That's great, but this printer, and many others, cannot run high acceleration. Even with high acceleration, you'll still have issues with oozing during moves and lack of filament at line starts when pressure advance is required.

This post wasn't really constructive. The point is, pressure does not build linearly, and having other variables to control it based on speed would be nice.

@dc42:

Have you established that reducing pressure advance improves the quality of the higher speed corner in that print? If so, how much did you need to reduce it?

Any thoughts on the above posts?

Cheers

Maybe there should be some kind of gcode command to enable safe movement protection

I'd think it could have a few parameters

S0 - disabled, no movement locks
S1 - enabled, no movement until homed
S2 - All moves have S1 enabled until homed
S3 - Z axis prevented from moving down until homed

or something

@deckingman:

@nyt

Good work.

I've done quite a bit of testing with pressure advance but only at high speeds so what you've discovered is useful. Link to my blog here. https://somei3deas.wordpress.com/2018/01/15/an-attempt-to-investigate-pressure-in-the-extrusion-system-with-a-diamond-hot-end/

From that testing, it appeared that pressure increases as print speed is increased but only up to a point, and thereafter seems to remain fairly constant. i.e. pressure increases up to a certain speed and further increasing the speed does not further increase the pressure. That is of course a somewhat subjective statement based on empirical observation - we'd need to fit a transducer of some sort to be able confirm that. However, it does seem likely.

So my suggestion would be that if we introduce an exponential variable to increase pressure advance with speed, then we also need to add a maximum speed limit beyond which the pressure advance remains constant. Or conversely, set the maximum pressure advance but introduce a tapering effect so that pressure advance is applied in the range zero to maximum over a print speed range of zero to some threshold value. (not sure if I explained that well).

Interesting. I wasn't sure it was remaining constant beyond a certain speed, just that less was required as speed increased It would be awesome to be able to graph this with a pressure sensor, but that's more effort then I can see spending on this. In this case, I'd use the variable to limit pressure advance as speed increases, with a value less than 1.

In the end, I just want to see it working reliably…. Using a factor of 10 and an exponent of 0.3 would get pretty close, for example using the speeds above...

The PA value would be multiplied by this...

10 * ( 75 ** 0.3 / 75 ) => 0.48691944197021614

10 * ( 30 ** 0.3 / 30 ) => 0.9247303715573938

also love the dimming

This time with a 0.4mm nozzle since it was loaded up… volcano with ruby nozzle 0.2mm layer height

Maybe add a factor and exponential variable to tune the equation as necessary? Thoughts?

gcode: https://pastebin.com/x4nu19ah

inner perimeter speed: 75mm/s
outer perimeter speed: 30mm/s

0.15 pressure advance on both:

0.08 on inner, 0.15 on outer:

The graph shows you speed per layer. The right of the x axis is your layer.