Flow rate calibration

Flow rate calibration

So, I've noticed that different slicing software tends to have different ideas about the required flowrate for extrusion and this results in quite different results for the same printed object. In particular, when I moved from SLic3r to Kisslicer (after too many frustrations with Slic3r producing weird artefacts and generally being a bit flaky) I found I had to significantly adjust the flow rates in Kiss to achieve a similar surface finish to the models I was producing with Slic3r. So, as I find myself telling people that Kisslicer is worth a try fairly frequently and that they will likely need to adjust their flowrates, I've documented the process I follow to dial in the flow rate below. You may note that I've not suggested the resulting flow rate changes are translated into a revised steps/mm for the extruder in your firmware of choice, this is because - as these values change with slicers - it's more sensible to allow the slicer to define the flow rate.

This guide assumes you have already correctly set up your steps/mm for X,Y ,Z and E axis. You also need to ensure your extrusion temperature is correct for your chosen material.

Firstly, you need to be using a host application that allows you to vary the flow rate during printing (like repetier host). Alternatively you can use Gcode command M221 S70  where the S value is the percentage adjustment made to flow rate.

1. Slice a 20x 20 calibration cube with 100% infill, your layer heigh of choice and all other settings configured to defaults
2. Send the resulting code to your printer and get it printing.
3. Wait until the cube is 25% complete – this ensures any layer ‘squashing’ that may have occurred as a result of initial layer 1 compression will have resolved itself
4.  Dial back flow rate down to 70% using the flow rate slider in Repetier or M221 S70. Let it print a couple of layers and then pause the print- it’s then worth moving the hot end away from the print to avoid it oozing onto the object and to allow you to see the print surface.
5. Inspect the print; the lines of the infill should now have noticeable air gaps between them – should look something like this (credit to Sublime's Tantillus guide for this picture)
6. Recommence the print job, and increase the flow rate by 5 %, let it print 3 more layers then pause and inspect. Rinse and repeat until the air gaps are no longer present.  I then tend to bump up the flow rate by 3-5 % percent to accommodate for variations in filament diameter.
7. Record the final % value you have for flow rate.
8. Apply this value to your flowrate modifier in your slicer software (Flow tweak in ‘Materials’ tab in Kisslicer, Extrusion multiplier ‘Filament Settings’ tab in Slicer, ‘can’t remember’ in Cura).
9. Re-slice the model and print again with flowrate set to 100 in the your host software.