Mount P.,Mount PrintMore wrote:Why is it important to set the filament parameters in the FFF? What about the extrusion process is handled differently from a mathematical perspective if you set a filament diameter and extrusion multiplier in the slicing parameters versus using the override at run time? This is a question I've posted before at somepoint and the responses I got at the time led me to believe this wasn't an issue.

I tend to run copies of the same files over and over or in various colors, so I very much like not having to recreate my gcode files just because I put on a new roll. I literally run these calibration parts, take the measurements, write the override I want to use on the side of the spool with a Sharpie, and then swap around spools at will while running off various parts.

I'll get some pictures of the test patches and post them soon. Perhaps that will help spur some further discussion.

Your question prompted me to "shut up and do the test". So I took a model, sliced it with my usual extrusion multiplier (0.94), then ONLY changed the extrusion multiplier (this time to 1.10) and sliced again, and compared selected regions of the two G-code files. Here are some snippets from right at a layer change:

ExtMult = 0.94:

Code: Select all

```
; layer 48, Z = 9.58
G0 X76.37 Y98.13 F12000
G0 Z9.51 F1200
G1 E-0.05 F1000
G92 E0
G1 X76.37 Y126.13 E0.9192 F3150
G1 X104.63 Y126.13 E1.8469
G1 X104.63 Y118.13 E2.1095
G1 X108.37 Y118.13 E2.2323
G1 X108.37 Y127.241 E2.5314
G1 X116.63 Y127.241 E2.8025
G1 X116.63 Y118.13 E3.1016
G1 X124.37 Y118.13 E3.3557
G1 X124.37 Y156.87 E4.6275
G1 X105.63 Y156.87 E5.2426
G1 X105.63 Y126.87 E6.2275
G1 X75.63 Y126.87 E7.2123
G1 X75.63 Y98.14 E8.1555
G0 X75.63 Y98.13 F3150
G0 X76.37 Y98.13 F3150
G92 E0
G1 E-0.6 F1000
G0 X115 Y130.869 F12000
G1 E-0.05 F1000
G92 E0
G1 X114.644 Y130.886 E0.0117 F3150
```

Code: Select all

```
; layer 48, Z = 9.58
G0 X76.37 Y98.13 F12000
G0 Z9.51 F1200
G1 E-0.05 F1000
G92 E0
G1 X76.37 Y126.13 E1.0756 F3150
G1 X104.63 Y126.13 E2.1613
G1 X104.63 Y118.13 E2.4686
G1 X108.37 Y118.13 E2.6123
G1 X108.37 Y127.241 E2.9622
G1 X116.63 Y127.241 E3.2796
G1 X116.63 Y118.13 E3.6296
G1 X124.37 Y118.13 E3.9269
G1 X124.37 Y156.87 E5.4151
G1 X105.63 Y156.87 E6.135
G1 X105.63 Y126.87 E7.2875
G1 X75.63 Y126.87 E8.4399
G1 X75.63 Y98.14 E9.5436
G0 X75.63 Y98.13 F3150
G0 X76.37 Y98.13 F3150
G92 E0
G1 E-0.6 F1000
G0 X115 Y130.869 F12000
G1 E-0.05 F1000
G92 E0
G1 X114.644 Y130.886 E0.0137 F3150
```

So, as far as I can tell from this simple experiment, you are absolutely right: no, it doesn't appear to make any difference whether you adjust the extrusion multiplier when slicing or online with the knob in the machine control panel. But that's assuming what the online override does. Sorry, I'm not THAT good a C programmer to pick through the firmware and figure out what the M-code for the extrusion multiplier override actually does!

Touché.

Dale