flow ratio on first full filled top layer
 
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PetBel
(@petbel)
New Member
flow ratio on first full filled top layer

I have a problem with the flow ratio of the first full filled top layer. As you can see in the two following pictures, the flow ratio on the first full filled top layer is about twice as high as on the following full filled top layer. Is there a way to adjust this. Such a high flow ratio is too much for my 0.4mm nozzle. The flow ratio on all other layers is constant at 3.5mm3/s.

Posted : 30/07/2021 7:18 pm
Neophyl
(@neophyl)
Famed Member

Set a max volumetric flow rate suitable for your nozzle/extruder/filament in either the filament profile or the print profile.  You can set it in either place and it will use the lower value.

https://help.prusa3d.com/en/article/max-volumetric-speed_127176   

Posted : 30/07/2021 9:50 pm
PetBel
(@petbel)
New Member
Topic starter answered:

Ok, I see. Thank you.

But like this the print speed is reduce to 50% for the layer. Is there no option to tell the slicer that I dont want 200% of material on this first full filled top layer. A little bit more because ther are "holes" from the infill underneath to bridge is ok, but 200%.

If this is hard coded into prusa slicer and there is no option to set it to another value, is there a wishlist for new functionality for prusa slicer?

Posted : 31/07/2021 5:50 am
JoanTabb
(@joantabb)
Moderator
RE: There is more than just Volumetric Flow to consider

Hi Petbel
Volumetric Flow Rate is an indication of how fast you are using filament, not as you appear to believe how fast filament is being extruded per millimetre travelled, Maximum volumetric speed, is an indication of how fast the extruder can melt the incoming filament to a consistency suitable for printing.  If your printer exceeds the ability of the extruder to melt filament, the extruder will jam. 

During printing, Actual volumetric Flow rate is compared against the Maximum volumetric Speed set in the slicer profile, and as the printer approaches Maximum volumetric Speed, the printer  slows the print movements  to maintain the ability to melt filament successfully. 
Maximum Volumetric Speed, is set in 'Filament settings > Advanced' in Prusa Slicer and typically  varies from 1.35 Cubic mm  per second, for 'Semiflex' to 15 cubic mm per second for PLA 

The values that actually  affect the quantity of filament extruded per millimetre of travel are.

Extrusion multiplier  (which the is used by the slicer, to calculate the expected amount of filament required based on millimetres travelled, speed of travel thickness of extrusion and width of extrusion). 
and
Flow rate  (Which is used by the printer firmware to change the  filament extrusion values calculated by  the slicer, and make them either larger (Flow more than 100%) or smaller (Flow less that 100%).  
Standard Prusa profiles contain a 'Conditional' equation to affect Flow Rate. 

M221 S{if layer_height<0.075}100{else}95{endif} this effectively lowers the Flow rate  if the layer height is 0.075mm or thicker

in the two images below, you can see that  the volumetric flow varies significantly for the same print, dependent upon which type of filament is being printed (without changing anything else)

In the image below, the Filament is set to Semiflex, and all layers and features are restricted by the 'Maximum Volumetric Speed', set for that filament type     'MAX Volumetric Speed 1.35 cubic mm  per second'

In the image below, the Filament is set to Prusament and all layers and features are restricted by the 'Maximum Volumetric Speed', set for that filament type     'MAX Volumetric Speed 15 cubic mm per second'

In the image below, the Filament is set to Prusament , and all layers and features are restricted by the 'Maximum Volumetric Speed', reset for that filament type     'MAX Volumetric Speed 0.2 cubic mm per second'

as above you can see that you can vary the volumetric flow rate by changing the  maximum volumetric speed value in Slicer. 
AND
you can see that if the Maximum volumetric Speed is High enough, the volumetric flow rate can change dependent upon print speed for the various elements, as shown below in a segment of the middle image above

I hope this helps you understand what is going on. 

regards Joan

I try to make safe suggestions,You should understand the context and ensure you are happy that they are safe before attempting to apply my suggestions, what you do, is YOUR responsibility. Location Halifax UK...
Posted : 31/07/2021 1:37 pm
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