Firmware Speed Limit  

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Nomad965
(@nomad965)
Trusted Member
Posted by: @bobstro
Posted by: @nomad965

I just noted something in the startup code under prusa slicer you entered the extrude override:

M221 S{if layer_height >= 0.32}90{else}100{endif} ; compensate for thick layer heights

A bit of explanation: If you use a default Prusa profile, you'll find this line:

M221 S{if layer_height<0.075}100{else}95{endif}

Basically, that line will use 100% extrusion for layers below 0.075mm and 95% for all other prints. As @neophyl notes, there is a long, misty history associated with this and Prusa has adjusted the line over time. There's a post somewhere here on the forums from Jo Prusa himself in which he explains that the original Slic3r code base tended to over-extrude above a certain layer height, so this was a brute-force fix. I'm surprised Team Prusa hasn't worked on the underlying issue in the code, or haven't removed this line if they have.

I very rarely print below 0.08mm, and found it frustrating to be carefully calibrating settings for fine prints only to find the slicer was overriding them, so I completely removed that line in my early versions. I do switch between slicers (though not much these days as PrusaSlicer has improved), so this was very annoying.

I also print with a wide range of nozzles, often swapping between 0.25 and 0.8mm nozzles in a single day. I find that over-extrusion is a mostly problem with larger nozzles (presumably due to lower back-pressure in the nozzle leading to increased flow). Thus I've gone with my brute-force line:

M221 S{if layer_height >= 0.32}90{else}100{endif} ; compensate for thick layer heights

This just changes it to "if printing big chonky parts where quality isn't crucial, reduce extrusion" and lets me use this printer profile with all my nozzle sizes with good results. I really need to move that line down to "final print adjustments" since it's definitely a user preference. Thanks for the feedback.

Not really sure how this affects the extrusion multiplier, since I set the extrusion multiplier after re-calibrating
with the new layer width, say I was on 0.45 and now running 0.48 I would redo the extrusion multiplier and set it for
that layer width. If using the M221 would that have an effect on the set extrusion multiplier. ?

To answer your question: Unless you're using layer heights of 0.32mm or higher, that line won't have any effect. If you are using thicker layer heights, it will drop extrusion overall by 10% (well, multiply by 0.9), so this will be a reduction in addition to any slicer settings. Think of M221 as a final multiplier applied in addition to all your slicer settings.

I want to stress: My examples are just what I'm using. I'm not pushing these are "magic profiles" or anything of the sort. They work well for me and serve as examples for others. Feel free to comment things out and experiment. Again, thanks for the feedback. I'll expand on the explanations.

 

 

Good thing I asked, since most of the time am printing with maximum layer heights on any nozzle from 0.4 to 0.8 so just needed to be aware of it. Thank you for the valuable feedback.

Prusa i3 MK2s MK2.5s Mk3 Mk3s BearPrusa Zaribo 320 - Kit Build - Rc Driver - Tweak freak...
“I know nothing about surpassing others. I only know how to outdo myself.” -Bushido-...
Posted : 11/06/2020 6:20 pm
Nomad965
(@nomad965)
Trusted Member

@neophyl

Thank you for the feedback, I started using it a couple of days ago as well, was using my own, but find bob's profile covering all the requirements that I need for now till I can find more to consider.

Prusa i3 MK2s MK2.5s Mk3 Mk3s BearPrusa Zaribo 320 - Kit Build - Rc Driver - Tweak freak...
“I know nothing about surpassing others. I only know how to outdo myself.” -Bushido-...
Posted : 11/06/2020 6:22 pm
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