Steps per mm vs Extrusion Multiplier

[Jimustanguitar]

I'm a little confused about what to calibrate. There are excellent instructions for getting a perfect .55mm thin wall cube by adjusting the extruder flow rate (which I thought you were supposed to use as a multiplier to calculate a new steps per mm settig), and it's well documented that you should adjust your steps per mm in the EEPROM to get the correct length of filament fed into the machine.

http://forum.seemecnc.com/viewtopic.php?f=54&t=1163
and
http://forum.seemecnc.com/viewtopic.php ... 182#p11182

It seems that both of these processes are adjusting how much filament is fed to the hot-end, but when I perform the steps I get different values (by about 15%). Which calibration is supposed to affect which setting in EEPROM and Slic3r? Am I applying the wrong calculation to the wrong place? Does Slic3r use the extrusion multiplier in a special way to make this difference work out?

Thanks in advance for the tip, I'll edit it into my calibration guide! Jim

[cambo3d]

one is for setting your steps per mm correctly. steps per mm is adjusted to match your board either 1/16th stepping or 1/8stepping for older boards. once you set this, dont mess with it again.
just like your xyz steps per mm, you dont adjust these to set your height do you? no you don't.

extrusion multiplier is for dialing in the correct amount of extruded plastic to get the correct thickness. I believe this setting speeds or slows your extrusion rate. slicer does this for you.

in the case of a 3d printer, i could see how you could use the steps per mm to adjust the amount of filament. but that isn't really what its intended for. steps per mm is set so that when you travel say 100mm your machine will physically travel 100mm. if your steps per mm is off. it will be either short or too long.

[Jimustanguitar]

That all makes sense. I guess the part I'm confused about is: if you dumb it all down and just look at the amount being extruded, aren't these both ultimately adjusting the same thing? One is changing the slicer instructions before generating gcode and the other is just changing what the machine does with that gcode, right?

The fact that I'm getting two different "right answers" with my measurements is what has me pondering this.

Thank you for the advice, I will definitely give it a try and see how it changes my prints!

[cambo3d]

if your extruder steps per mm is set correctly and you extrude 100mm of filament into free air, you should get 100mm of filament when measured with a ruler.

[geneb]

Any easy way to test this is to cut a short length of filament. Mark two points 100mm apart and then load it into the extruder so that the first mark is even with the clear plastic feed hole on the bottom of the extruder. Run it for 100mm and the second mark should appear in the same location as the first.

g.