Feature request - Change flow rate during printing

We are all on a learning journey, verbiage will always be an issue because there are many who English is not their spoken 1st language and even more who this is their first experience with 3D printing, might be helpful to remember that too

Sure, that’s all fine. I’m just saying, if I’m learning something new, then I’m glad when people try to help and give me advice or share information.

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Extrusion multiplier can be changed on every printer on the fly that I have used except bambu lab. I am only responding to these because I need it right now. Flow calculator on the lidar wasn’t correct and I’m 6 hours into a print on HTNCF25. Don’t exactly want to stop and throw away $100 in material because I can’t change extrusion multiplier. Would be a very nice thing to add to the software for times where it doesn’t calculate correctly because either the sensor is dirty or its black and hard to pick up sometimes.

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Lets argue semantics!!

They aren’t completely different things. What you’re calling “flow percentage” is specifying print’s flow rate as a percentage scaling of the base flow rate, which is what’s been clearly described several times now. For over a decade 3d prints have allowed adjusting the flow rate up or down by a percentage, and have used that terminology. If you want to invent new terminology for yourself, feel free to do so, but please don’t insist that everyone else change the industry’s standard terminology just because you’re confused by it.

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First of all: I’m not trying to argue with anyone. There is a reason why this setting does not exist. For that it is necessary to understand the difference in these terms.

I’m not inventing anything new. I’ve taken the definition from the the marlin gcode docmentation. Inventing a new term that is not used anywhere woudn’t make any sense.
So it is standard terminology and like I previously described: Sadly many manufacuters do confuse the terms (by that I mean mostly chinise printer manufacturers).
You can look it up and see for yourself.

What you’re calling “flow percentage” is specifying print’s flow rate as a percentage scaling of the base flow rate, which is what’s been clearly described several times now

Here is the deal: It’s not correct. The printer does not have a “base flow rate” after slicing in the data. All it has is a bunch of commands that tell it how much the extruder is supposed to move in a specific time. And this is different for almost every single command in the gcode fle. So this ist not a flow-rate value at all. And the calculation can not be reversed because 3D-Data is not part of the gcode file, which would be needed for that reversal. All the printer can do is to multiply the extruder speed value with a factor.

Btw. the lidar already does apply a flow percentage in a way, except that it’s not a single value, but a range of values for various accelerations and speeds. That’s why it scans these printed patterns that are printed in multiple lines, each with different speeds.

About the similarity argument: No, these values are fundamentally different, because the calculations work on an entirely different set of data. Raising percentages will always be flawed, because the flow percentage is constant over the whole print and flow rate is not. Flow percentage remaps the motor speeds and throws off accelerations and jerk. That means this is a linear operation.
Changing flow precentage also throws off any auto-calibration that is done by the lidar, while rasing flowrate would only shift it relatively to the actual calculations, which depend on the 3d representation of the model itself, that is not present after slicing. That means flow rate is a non-linear operation.

If you change flow percentage, then the extrusion will be too much in some places of the print and still too little in other places. Raising flow-rate (which you actually get right when doing manual calibration for your filament in the slicer) will result in very consistent results instead.

That’s why you can’t compare them.

Here is why Bambu Lab did not and verly likely will not introduce such a setting:

  1. If you get underextrusion (or overextrusion) then the filament is not dialed in properly - which is easy to fix with the help of the slicer. Why should a developer introduce a setting that causes more issues than it solves when the fix is actually not a fix but a hack
  2. Throwing off lidar calibration results due to messing with the calibration data after the fact would result in more support requests due to inconsistent prints with the lidar being enabled.

I mean I could be wrong and they might still implement it if the demand is high enough. Although I doubt that and would be surprized if they did.

Personally I avoid using the lidar because it is flawed as well due to many reasons. I think it is tuned to rather underextrude than overextrude. At least that’s what I would do if I had to design such a system. Overextrusion can cause a lot of issues like skipped steps due to collisions with the print and a properly calibrated filament is very unlikely to fail this way (unless it’s printed to fast and deforms to obstruct the movement path of the nozzle). I’ve seen broken hotends due to overextrusion.
And most people recommend tuning their filament manually. Especially when it is expensive. One might think it wastes money, but it’s actually the other way around: It reduces print failures in both ways: no underextrusion and no overextrusion.

You are something.

So many words. Very little said.

Essentially every other printer on the market can have the “flow” adjusted during printing. this is not a “new feature” and it does “cause more problems than it solves”.

You seem to think the lidar is doing some sort of very advance calibration, but it is not. It is tuning 2 things:

  1. The “flow ratio” (a multiplier applied to all extrusions)
  2. The pressure advance coefficient (the strength of the non-linear PA compensations applied any time the rate of extrusion changes)

We are only talking about #1 here. You could affect the “flow ratio” any number of ways (filament diameter, extruder steps/mm, filament flow ratio, or a “flow multiplier” tuning setting).

Yes I know what the Lidar is doing and you seem not to understand the “little that was said”, or why do you repeat what I already said. I explained the Lidar is flawed, for the same reason.
However the lidar does not apply one fixed value to the flow ratio, but actually multiple values for various feeds and speeds. A fixed flow ration would interfer with that and that’s why this is not a feature you will see Bambu Lab implement.
You should know that BL plays safe in stuff like that and they have more tickets that they can deal with, so I still don’t think they will ever implement it.
Just wait and see…

…the adjustment would also be a multiplier, not a ‘fixed flow ratio’

You know, the same way every other printer that has this implements it, because that works just fine and doesn’t have any of the issues that you’ve come up with from your own misunderstanding.

Yes, but no other printer comes with auto-calibration that whoud be messed with.

All the auto cal does is set the same setting you’d set manually. You know, as you do on the P1’s

This is incorrect. While, yes it does set the same setting, but it is variable based on the speed. So it changes this value for every move. You can’t do that with a single selection and that’s why it interferes with the auto calibration.

No, it’s not, it’s a single PA compensation, the bambu firmware unfortunately doesn’t do variable PA like some older printers could - as you’d see if you try some TPU at decent flowrates (softer filaments end up more and more assymetrical on their PA requirements), you’ll see the exact same issue on the X1C as you do on the P1’s - they underextrude on acceleration and overextrude on deceleration because it’s a single setting and it’ll just select halfway between the two ideals.

The A1 actually has better tech for that as it could set it live if the eddy current sensor was fast enough to sample on the fly.

Yes it is. At first I though the same as well. As stated above, I’m a software engeneer and I already tried implementing a mechanism to adjust flow percentage. I hacked the can-bus signal and quickly discovered the ever changing values that ware completely different from what the gcode commands. They were not changed by one single percentage value. But it changed inbetween prints and looked more like some kind of value-maping. I would have to fight the calibration values to overcome this, so I didn’t invest any more time into it. Nowadays I rather calibrate my filaments in advance in the slicer and turn calibration off completely. And that gives better results every time than any guessed adjustment.

Of course they’re different to the g-code - the firmware applies the pressure advance, not the slicer.

Yes I know, I mean they wer not offset by one percentage value as I expected.

I compared each command in the gcode file with the extrusion speed that was supposed to be set and compared it to what it really was. Then I had a percentage value that should be consistent for the whole print. The next command was a significantly different percentage value and that applied to all commands.

Then I ran the print multiple times and even the same command lines were different because of the new calibration that was done for each print.

PA is applied as a factor to the acceleration change of the extruder, not a flat rate on the extrusion amount during acceleration/deceleration, that’s why.

It’s incredibly easy to add adjustment on the fly, none of this is an issue. It’s not an issue when you speed a print up even though the dynamics change because of the former (well, sorta, the pressure advance asymmetry comes in again as the extruder pressures rise - again something you’d see on soft filaments if you speed a print up with the ‘sport’ or ‘ludicrous’ modes - but more users don’t really need things that finely tuned)
Fine tuning prints on the fly can help massively with prototyping a process. I assume the reason it’s not there is mainly because everything is geared at new users and automating as much as possible. Hide anything they can mess with that might make prints and diagnosis worse.

Still it’d be nice to have under a dev menu, much like the extra slicer options.

Maybe I did something wrong along the way, but the data didn’t seem like there was a pattern to be found.

I think as the developer they could do better than that with the lidar unit. At least on the X1C. For the P1P / P1S such a setting would be easier to integrate.
Though I still think flow percentage adjustment is just a hack that could lead to hotend damage, but that could also be forced with the slicer.

Anyhow whatever the reason really is. Leaning towards new users does sound like one. I still don’t think we will see this feature anytime soon.

Maybe moreluck from the guys who implement the alternative firmware (I forgot the name of it).

Anyone who’s done a lot of LW/Aero/Foaming PLA printing will be looking for this - Just started a new aero print today, first one on P1S and went searching for it :neutral_face:

I’ve printed heaps of LW-PLA on other printers that had this “Feature”, from DIY repraps, Flashforge Adv, Ender 5 etc - it doesn’t complicate anything and is an absolute necessity imho.

+1 for feature request :slight_smile: