Flow rate, what is it

I keep hearing people mentioning the flow rate but there is little on it available. I believe it adjusts the amount of filament that flows out of the tip but for what reason. Why do I want to use it. There is also the line width in Cura (which must be pushing more filament out to increase the width), does that do the same thing.

Hey @Loosenut the flow rate is basically an override for all extrusion-related operations. A lot of people use it to “clean” up prints that show Bubbles in the corners or Elephants’ foot. It’s a way to globally reduce or increase the amount of filament extruded.

Let’s say that your extruder runs 100 steps /mm and this is set in the firmware. For PLA and PETG this works great but for TPU it looks a little “fat”. You can set up a profile just for TPU with a flow rate of say .95 which means that when using this profile you are only extruding 95% of the filament you would ordinarily extrude without changing any other parameter.

Let the truth be told, almost all of the “factory” slices I see come on SD cards from the manufacturer have the Flow rate set to around .97 or .98. Just a coincidence? not really sure.

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OK thanks. I just leave mine at 100% and all is well…I think.

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Flow and extrusion multiplier are the same thing. It is a fast and easy calibration for the extruder.

Changing flow compensates for different density and expansion properties of different filaments.
If you were printing .4mm lines and your top layer had ridges in it your flow is too high. If it had gaps between the lines your flow is too low.

I calibrate it using the teaching tech method with a single wall cube. If the wall of the cube measures different than the line width setting I adjust my flow

It is something I calibrate for every single type of filament. My values usually come out to between 85-97ish from what I remember for the 8 or so varieties I have profiled. None of them have been 100.

I was watching a video from CNC kitchen about a type of foaming TPU that expands more with hotter print temperatures. As he put the temperature up he had to adjust the flow down significantly, into the 60% range, to maintain the right size line. That’s an extreme example but illustrates how different filaments behave differently and need to be adjusted for.

Changing your line width is different because it is telling the nozzle to move over that amount for each line. I believe it compensates for the volume of filament being extruded when you change that setting since it needs to push it more filament if your line is wider.
If you put your line width up to say .5 and you had gaps between the lines you would still need to adjust flow to compensate.

So long story short, flow and line width are for two different things and you should calibrate your flow for every filament to get the best print results.

this is good info, I hadn’t considered testing between filaments, do you find filament colour makes a difference?

@Glenn I haven’t been changing it between colors so far but I should be double checking it.
I have switched between clear and black petg from the same brand and have not seen any indication that the flow should be changed. That was printing parts with tight fit tolerance and there was no issue. That isn’t to say that different filaments wouldn’t behave differently between colors though.

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Personally I have not noticed much (any) difference between colours. I tend to print a cube every now and again, somewhat randomly. I tend to sit in the 1.04 area. I have noticed that CF (PETg and PLA) I need to bump that to 1.06-1.08.

Knowing that you use Prusa slicer, are you saying that most of your filaments are under extruding at default values if you have to bump up above 1?

I have only used Cura so I’m not really familiar with the details of Prusa slicer.
My experience with Cura is that every filament has needed to be dropped below the default of 100% otherwise they all over extrude.

mine tends to slightly under extrude. I have flow rate controls as well it is 94. The flow (extrusion multiplier) is fixed to a filament so I can tune filament to filament in my case I have not found it is needed but for a few here and there. CF for example. The flow rate is on the printer and can be tuned live as needed. For small foot print things I might slow the printer for a while 10-20 layers say and perhaps add or subtract flow rate to increase adhesion or decrease elephant foot. Then return it to normal. I could do that in gcode but I have printed so much that I find I can judge the actual print as it is made more accurately.