Flow rate compensation factor. What is it?

[d-lee 0]

There is a couple of settings in the Experimental section in Cura 3.6.0. "Flow rate compensation factor" & "Flow rate compensation max extrusion offset". What do these two things affect? 

 

I couldn't find any documentation or explanation for these two settings. The tooltips in Cura for these two are a bit cryptic. 

[nallath 1,120]

Some materials are a bit strange when you extrude them. If you ask for 100 (whatever the unit is, doesn't matter), some materials only extrude 96 (or something like that).

This is mostly an issue for machines that have flow measurement (Such as the S5). There are basicly 2 things that you can do to fix this. If you don't have a flow sensor, you "simply" pre compensate for this factor. So instead of asking for a 100 if you want 100, you ask for 105 in order to get a 100. The problem with that is that if you have a flow sensor, it will give a warning (Because you asked for 105 and got 100, which should be seen as underextrusion).

Those two settings are meant to be used to solve this problem.

[d-lee 0]

Got it. Thank you for explaining it!

[stema84 1]

so these settings doesn't have effect on "flow rate" at all, these are indications for the flow sensor to compensate, how to interpret what actually happens? Because it's set to 90% by default and I really like to have control over settings, but here, I'm puzzled. Your description is good, but "you "simply" pre compensate for this factor" is not clear.

Edited February 20, 2019 by stema84

[GabrielStaples 1]

Cura slicer explanation of settings "Experimental" --> "Flow Rate Compensation Factor" vs "Material" --> "Flow":

 

Quote

so these settings doesn't have effect on "flow rate" at all, these are indications for the flow sensor to compensate, how to interpret what actually happens?

 

The following is according to my understanding.

 

No, I believe this "Flow rate compensation factor" does have an affect on flow rate, it just does it withOUT further triggering flow rate sensor errors. 

 

Let's walk through an example:

 

Imagine your "Flow" setting under the "Material" settings section is set to 100% and your "Flow Rate Compensation Factor" under the "Experimental" settings is also set to 100%. BOTH control the actual flow rate by changing the commanded flow rate to the extruder, but the "Flow" setting also sets the "expected" flow rate used by the flow rate sensor, while the "Flow Rate Compensation Factor" does *not* also set the "expected" flow rate used by the flow rate sensor. 

 

Imagine you have a flow rate sensor on your printer and it keeps throwing warnings that your actual flow rate is 95% when the commanded flow rate is 100%. To compensate, you need to increase your flow rate by a factor of 100%/95% = 1.053. So, multiple that by your current commanded rate of 100% and you get 1.053 x 100% = 105.3%. Now, if you increase your commanded flow rate to your extruder from 100% to 105.3% you'll end up with an actual extrusion rate of 105.3%*95%/100% = 100%. It is reduced by the 95%/100% = 0.95 factor as a result of the material's resistance to extrusion. Each material you use can have a different resistance-to-extrusion constant, which is an indicator of the material's slipperiness, excessive thickness, excessive thinness, or viscosity/higher melting temp.

 

For materials with a higher resistance-to-extrusion constant, for which you must compensate, there are 2 ways to increase the commanded flow rate to 105.3% so that you end up with an actual flow rate of 100%. One of these options to increase the actual flow rate will continue throwing the under-extrusion warning, and one will not:

 

1. Option 1: Change the "Flow" setting under the "Material" section from 100% to 105.3%. Now, your actual flow rate will become 105.3%*95%/100% = 100%. BUT, changing this setting also sets your flow sensor's expected flow rate to 105.3%. Since you are getting only 100% instead of the commanded 105.3%, the flow rate sensor continues to throw under-extrusion warnings even though the extrusion is now exactly perfect!
2. Option 2: Change the "Flow Rate Compensation Factor" under the "Experimental" section from 100% to 105.3%. Now, your actual flow rate will become 105.3%*95%/100% = 100%. AND, changing this setting does NOT also set your flow sensor's expected flow rate. Rather, the "Flow" setting under the "Material" section does! Since it is still set to 100%, and you are now getting an actual 100% instead of 95%, the flow rate sensor shows your extrusion is now perfect!

If you don't have a flow rate sensor, it doesn't matter which setting you adjust above. You can adjust actual flow rate using the "Flow" setting OR the "Flow Rate Compensation Factor" setting. If you DO have a flow rate sensor, however, you need to set the "Flow Rate Compensation Factor" under the "Experimental" section to both adjust actual flow rate AND to stop the flow rate sensor error at once.

 

Make sense?

 

Can an Ultimaker employee/Cura software developer confirm the above?

Edited June 5, 2022 by GabrielStaples