Zen and the Art of Going With the Flow Control

Well, color me stupid. Today I discovered something called Flow Control. From my reading it seems to be the amount of filament that comes out of the nozzle, regardless of how much the extruder pushes into the hotend. Of course I assume there’s a link between these 2 things but, apparently they’re not actually the same thing.

I found an article that referenced a bottomless & topless box (basically a fence) that’s supposed to have walls that are 0.8mm thick when printed. If the walls are too narrow the Flow Control needs to be increased, and vice-versa for walls too thick. Mine were quite thin; around 0.5mm to 0.6mm.

A little more research led me to discover that PrusaSlicer 2.2, which I’ve been gravitating toward the past couple of weeks, calls Flow Control Extrusion Multiplier (it’s located in the Filament item in the Filament tab).

My Extrusion Multiplier was set to 1, the default. I printed several test cubes, first with PETG, then with PLA. It turns out I need an EM of 1.85 for PETG and 1.70 for PLA. Using those values I was able to get walls very close to 0.80mm thick (0.79mm to 0.81mm).

I think that’s pretty close. What do you guys think?

Yeah. I had no idea I was underflowing so much. Today I tried changing the layer height from .24 to .12 and reprinting the test. It pretty much came out the same, so no need to have a different profile for that setting.

Check your wall thickness, and it’s size in relation to your nozzle size and flow rate.
I did wall thickness 0.5mm with 2 wall lines, which gave me perfect 1mm around each side

The test I used, Extrusion multiplier calibration by 3D_MaxMaker - Thingiverse, is basically designed to test wall thickness. Optimum for the test is walls 0.8mm thick. Mine are very close. I have not yet tried wall thickness so close to size of my nozzle (0.4mm).

This is an interesting test print: Fast edge over/under extrusion test by NirDobovizki - Thingiverse


Flow control or extruder multiplier is a way to compensate for the difference between filament types and also for a miscalibrated extruder. If you have a printer that supports saving to the prom you can recalibrate your extruder. Here is a video about the subject:

I found a YT video in which a guy explains that Flow Control is what you do after calibrating the extruder. He doesn’t even worry too much about extruder calibration: within 1 or 2 mm is fine with him. After that he uses a 1 wall thick bottomless, topless 20mm cube to set the flow rate to get as close to 0.4mm wall thickness as he can. He errs on the side of a bit too thick, rather than too thin. The way he explains it made a lot of sense to me, since I’d been having trouble trying to understand the relationship between flow control & extruder calibration. It also provides a way to calibrate different slicers to a given printer since, apparently, they don’t all do things exactly the same.|
The video is here: // HOW TO // Extruder + Flow Rate Calibration - YouTube. I don’t know the guy’s name, but he looks an awful lot like he could be Elon Musk’s son. ?