Why is Flow set to 95 as standard?  

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Spacemarine
(@spacemarine)
Estimable Member

I'm on Firmware 3.5.1 and I noticed that Tune -> Flow is set to 95 as standard. I've seen some other people comment on this, but I wasn't able to find an explanation as to why this is the case.

It is my understanding, that flow should be set to 100 as standard and only be changed if there are any problems, that you can't trace back to the real causes. (Like wrong filament diameter, etc.)

Setting the flow to 95 as a default means, that all other (correctly calculated) values are a little bit off. Maybe too small to notice, but still not correct.

Anyone can explain why this value is set to 95 as standard?

Posted : 01/01/2019 2:20 pm
jbinfl
(@jbinfl)
Reputable Member

Just as a data point, I noticed prior firmware had the flow as 95 set as well... I was on 3.4.1 until yesterday and it was also set to 95...

I did the extrusion calibration test at https://shop.prusa3d.com/forum/prusa-i3-kit-archive--f84/extruder-calibration-t2033.html and it extruded 95 MM of filament and not 100 MM with firmware 3.4.1. This thread is old and appears to be for MK 2s, but my MK3 clearly extruded 95 MM when I told it to extrude 100 MM for some reason ❓

I also am not sure of the reason, but know my printer is extruding 95MM of filament. Is it possible that there is an untold reason for it? could be, but it does seem unusual... I would like to know as well.

Strange women, laying in ponds, distributing swords, is hardly a basis for a system of governance!...
Posted : 02/01/2019 3:42 am
bobstro
(@bobstro)
Illustrious Member


I'm on Firmware 3.5.1 and I noticed that Tune -> Flow is set to 95 as standard. I've seen some other people comment on this, but I wasn't able to find an explanation as to why this is the case. [...]
You are most likely seeing the effect of a line in the startup gcode in Slic3rPE using one of the Prusa profiles or derivatives. If you look at the last line in the startup gcode, you'll likely see:

M221 S{if layer_height==0.05}100{else}95{endif}

There was a post on this long ago that you might be able to find that JP himself wrote explaining why the line was added. IIRC, it was something to do with the Slic3r code over-extruding on infill at lines > 0.05mm. This approach strikes me as something as a hack, plus it's limited to only 0.05mm. I've commented it out of all my profiles. Give that a try and observed the change under Tune -> Flow during a print.

My notes and disclaimers on 3D printing and miscellaneous other tech projects
He is intelligent, but not experienced. His pattern indicates two dimensional thinking. -- Spock in Star Trek: The Wrath of Khan...
Posted : 02/01/2019 4:33 am
jbinfl
(@jbinfl)
Reputable Member

Bobstro/spacemarine:

I think if found the post after going through 65 pages of JP (Josef Prusa) posts because I started from the oldest.... 😀 😀 Good Lord, that was informative.

https://shop.prusa3d.com/forum/others-archive--f66/updated-slic3r-pe-over-extrusion-and-cooling-solve-t12949.html#p59075

So, my understanding is, the default flow rate is set at 95 in the latest firmware ( and recent releases) as a result of the extrusion issue for printers that was brought up earlier this year which was indicated as from the slic3r defaults overextruding which was a fix for the overextrusion issue (mainly on the MK2 printers)? yes?

I do not want to start a war between MK3 and MK2 printer people, but I know my MK3 extruded about 95 MM on the 100 MM test i did today. If that is the case, then I am going to try adjusting the extrusion multiplier on my MK3 and see if that does anything... I do know that initially, I did not have any issues, but now I do. I know it is not easy since there are 2 different printers and there appears to have been an extrusion issue... I will test tomorrow and report if it did anything.

Strange women, laying in ponds, distributing swords, is hardly a basis for a system of governance!...
Posted : 02/01/2019 6:45 am
bobstro
(@bobstro)
Illustrious Member


I think if found the post after going through 65 pages of JP (Josef Prusa) posts because I started from the oldest.... 😀 😀 Good Lord, that was informative.

https://shop.prusa3d.com/forum/others-archive--f66/updated-slic3r-pe-over-extrusion-and-cooling-solve-t12949.html#p59075
That's it. The definitive answer to the OP's question is this:

All Bondtechs have exactly the same esteps and are calibrated very well, but the thing is that Slic3r naturally overextrudes a little. By coincidence about the same 5% as the MK2 were underextruding. It is caused by different calculation method of the volume compared to simple rectangular area model supposedly to make the Slic3r generated files more accurate.

[...] If that is the case, then I am going to try adjusting the extrusion multiplier on my MK3 and see if that does anything...

Before you do too much, try simply commenting that line out of the Slic3rPE startup gcode. You can see the M221 lines in the gcode when it's there, and not see it when commented out. I don't believe anything has changed in recent versions.

Interestingly, I'm having over-extrusion issues using big-fat layers over 0.32mm high. I've calibrated the filament extrusion rate using a 0.40mm nozzle and they're pretty much spot-on, but larger layer heights start to look like melting ice cream. I've changed that line to:

M221 S{if layer_height>=0.32}95{else}100{endif}

I'm not sure I like the results just yet, but it's promising.

My notes and disclaimers on 3D printing and miscellaneous other tech projects
He is intelligent, but not experienced. His pattern indicates two dimensional thinking. -- Spock in Star Trek: The Wrath of Khan...
Posted : 02/01/2019 7:30 am
Spacemarine
(@spacemarine)
Estimable Member

Thanks for shedding some light onto this.

I have to agree with bobstro on this. It seems to do the trick, but it is an "ugly" hack after all. The real error must lie somewhere deeper.

For now, I'll live with the 95, as my test-prints seem to be spot on so far. But if any problems will arise, I know where I might start to dig.

Posted : 02/01/2019 11:32 pm
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