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Introduction

In relation to this guide Flow rate or Extrusion multiplier (from here on out referred to as flow rate) refers to the slicer setting that determines how much plastic is being extruded. By default flow rate is typically set to 1.0 or 100% depending on the slicer in question. By setting the flow rate to 1.2 or 120% you are increasing the flow rate by 20%.

Why do I need to change the flow rate?

Different types filaments have different densities, and even different colours of the same filament brand can have different extrusion properties which can lead to either under or over extrusion which creates defects in the print quality that you obtain. Calibrating your flow rate will also help improve the accuracy of the printed geometry compared to the original geometry of the CAD model.

Before progressing with this guide it is assumed that you have already calibrated the esteps per mm so that when you extrude 100mm of filament the stepper motor is actually extruding 100mm of the filament. If you have not already done this please read the esteps per mm guide before continuing.

Another factor that you should look into before continuing is the filament diameter. The slicer, unless you are using a filament diameter sensor, assumes that the filament diameter is a constant. In reality, this is not the case filaments have a tolerance meaning that 1 .75mm filament can vary in size depending on the tolerance stated by the manufacturer, with higher quality filaments having smaller tolerances. These changes in size will be a variable that you won't be able to iron out completely, however, the effects can be reduced by taking an average filament diameter of the particular spool that you are working with and using the average figure instead of the 1.75, or 2.85mm that you have set in the slicer.

Steps that should be addressed before calibrating the extrusion rate.

  • Make sure you have the correct nozzle diameter setup in your slicer, and if necessary your firmware.
  • Make sure you have the correct filament diameter setup in your slicer and firmware (ideally this would be the average taken by the particular spool, but you can just use 1.75mm or 2.85mm).
  • Make sure the Nozzle is clear and not partially blocked, do a couple of cold pulls until the tip of the filament comes out clean.
  • Make sure the nozzle you are using hasn't been worn down, ie if it's a brass nozzle make sure it hasn't been used for any abrasive filaments such as wood fill, metal fills, glow in the dark or carbon fibre filled filaments.
  • Make sure you use a fixed extrusion temperature if you are not sure what temperature you should be using you should try printing a temperature calibration tower.
  1. Load the test model in your slicer of choice
  2. Slicers typically will use 20% as the value of the extrusion width, this is due to an effect known as die swell. so for example, if you are using a 0.4mm nozzle the wall thickness, track width or extrusion width should be set to 0.48
    • Slicers typically will use 20% as the value of the extrusion width, this is due to an effect known as die swell. so for example, if you are using a 0.4mm nozzle the wall thickness, track width or extrusion width should be set to 0.48

    • it is recommended to calibrate flow using a double wall thickness as this also allows you to judge the adhesion between the walls. so set the wall line count to 2.

  3. in order to actually measure the wall thickness you will need to make sure the model is hollow, set the infill density to 0%.
    • in order to actually measure the wall thickness you will need to make sure the model is hollow, set the infill density to 0%.

  4. you will not be needing the top and bottom layers for this test, so set the Top layers to 0 and the Bottom layers to 0.
    • you will not be needing the top and bottom layers for this test, so set the Top layers to 0 and the Bottom layers to 0.

  5. You can use a Brim to help with bed adhesion as the surface area is fairly small, this also gives you a place to write notes for future reference.
    • You can use a Brim to help with bed adhesion as the surface area is fairly small, this also gives you a place to write notes for future reference.

  6. Double check the print path using the layer view, you will have to select prepare for the path to show up.
    • Double check the print path using the layer view, you will have to select prepare for the path to show up.

  7. Take an average measurement of the wall thickness of all 4 walls using a pair of calipers. Ideally take 2 measurements per wall, ie 8 measurements in total.
    • Take an average measurement of the wall thickness of all 4 walls using a pair of calipers. Ideally take 2 measurements per wall, ie 8 measurements in total.

    • In this example the wall thickness is 0.72mm

    • New flow rate = (expected wall thickness ÷ actual wall thickness) x current flow rate

    • New flow rate = (0.96 ÷ 0.72) x 100

    • New flow rate = 133 or 1.33

    • you should take the measurements towards the top of the wall to avoid any errors cased by the brim or by the elephant foot effect.

  8. You may have to repeat this process a couple of times to dial in the measurements.
    • You may have to repeat this process a couple of times to dial in the measurements.

    • This time the average wall thickness is 0.92mm

    • New flow rate = (0.96 ÷ 0.92) x 133

    • New flow rate = 139 or 1.39

  9. The wall thickness now measures an average of 0.96mm.
    • The wall thickness now measures an average of 0.96mm.

Finish Line

One other person completed this guide.

Dan Rock

Member since: 06/07/2018

14,970 Reputation

28 Guides authored

One Comment

This might be a valuabe method to fine tune the flow rate, once the extruder is properly calibrated. But with the given example it becames an example of how to not solve a massive extrusion problem using the flow rate.

The only way to get a wall thickness of 0,72mm with two lines of material spaced at 0,48mm one to each other (C/L to C/L) is to get each line having a real 0,24mm width(!!!), with a gap of another 0,24mm between lines. I know, a good slicer might overlap a bit the real lines, that means it will work with 0,42mm-0,45mm distance between (C/L) lines, but still we get impossibly thin lines with 0,2mm gap between them.

Such a faulty extrusion process might have various causes, but none of them should be solved adjusting the flow rate.

I really hope you put in your example some imaginative figures to make it more understandable

Sergiu Irimie - Reply

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