Touradnik9
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Posts posted by Touradnik9
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2 hours ago, gr5 said:
So Cura does care if the filament is round versus if the filament is square because it calculates the flow coming out of the nozzle assuming that it knows the diameter of the filament going into the feeder and it knows the linear distance the filament has moved so it calculates the volume of filament extruding that way.
Cura doesn't care about the diameter of the nozzle - it assumes that the volume of filament going through the feeder matches that coming out of the nozzle (no leaks).
This is absolutely true. Cura relies on you telling it a reasonable value for line width. A value similar to your nozzle width.
Yes, cura does care about the shape of the filament. Instead of asking for filament diameter, a more accurate question would be 'filament cross-sectional area'. So, if you were to use square filament for whatever reason, you can rearrange the equation below to solve for D, or equivalent diameter, and that would produce exactly equal G Code values.
4 minutes ago, Touradnik9 said:Equating the diameter of the nozzle to the length of a side for a square nozzle does not make a lot of sense. The key parameter here is area.
Remember, we want the volumetric flow rate to be equal. So, for a nozzle with diameter, D, the equivalent square nozzle would have side length S equal to:
S = D*sqrt(pi/4)
So when you say 'the lines require slightly different amounts plastic', it is because the dimensions of the square nozzle are incorrect to begin with. According to this equation, for any linear distance of extruded filament, the amount of material will be exactly the same.
The shape of the extrusion will be slightly different of course, but that is beyond the topic of this thread I think. That is a much more complex issue. From a slicing perspective, the calculation is important to determine the rate and distances of the extruded filament in the gcode.
The biggest issues would be at the start and stop points, but the differences can be fixed or 'covered up' by adjusting your overlap percentages.
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Equating the diameter of the nozzle to the length of a side for a square nozzle does not make a lot of sense. The key parameter here is area.
Remember, we want the volumetric flow rate to be equal. So, for a nozzle with diameter, D, the equivalent square nozzle would have side length S equal to:
S = D*sqrt(pi/4)
So when you say 'the lines require slightly different amounts plastic', it is because the dimensions of the square nozzle are incorrect to begin with. According to this equation, for any linear distance of extruded filament, the amount of material will be exactly the same.
The shape of the extrusion will be slightly different of course, but that is beyond the topic of this thread I think. That is a much more complex issue. From a slicing perspective, the calculation is important to determine the rate and distances of the extruded filament in the gcode.
The biggest issues would be at the start and stop points, but the differences can be fixed or 'covered up' by adjusting your overlap percentages.
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The E values of all FDM, filament based printers are based on the same equation. That is, the conservation of volumetric flow rate:
where 'deposited' referes to the material exiting the nozzle.
The tricky thing here is that different slicers use different equations. I have found that the biggest difference is in the cross sectional area of the extruded mass, i.e. Aextrusion.
That is why I started this post.
The next biggest equation is how path spacing is calculated between adjacent paths. You need both equations to understand how the material will flow out of the nozzle, and how the material will bond with adjacent paths.
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This is an ideal world, which the slicer looks at to make its calculations. However, in reality, the cross-section will never be truly rectangular.
The center-to-center spacing between lines should therefore be slightly less than the extrusion width. Otherwise, the planar interface between lines would be exactly planar contact with minimal bonding between adjacent paths. But of course, for calculations I have seen that it makes the calculations easier when the spacing is equal to line width. This would allude to the fact that the width is actually larger than what is being used by the slicer.
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Hello,
No, you are exactly right. Cura will overestimate with a rectangular cross section compared to a circular cross-section.
So, if you are extruding more material with Cura's estimate, something else has to change. That something is the distance between path spacings ( I would guess, but Cura's code in not open source).
If you look at my post on Slic3r versus MC, the path spacing between adjacent extrusions are also different. Slic3r calculates path spacing as a function of both layer height and extrusion width, while in MC it is equal to the nozzle diameter. Both calculations are important when considering flow through the nozzle
But let's think about this: the 'rectangular' and 'circular' shapes for a second.
There is a huge difference between the geometry that the slicer assumes for flow calculations and reality. The slicer simply assumes a geometric cross section to aid in the calculations of the E values. This is a problem inherent in the fact that FDM printers utilize GCode to produce parts. Without this geometric consideration, it would be impossible to predict the E values, which are based on the conservation of volumetric flow rate.
So when it is stated that the filament extruded is 'circular' and 'not rectangular', I cannot see how that is possible. I think the correct answer would be neither because the shape is extremely variable and dependent on a huge number of variables, such as material flow, ambient temperature, nozzle temperature, head speed, layer height, etc. The shape changes as these variables change. From experience, I would say the shape is ovular, and changes with respect to these variables. As layer height is increased, the cross section approaches that of a circle. As layer height decreases, the cross section approaches that of slic3r's cross section.
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Burtoogle, I saw your reply, thanks! So it is a rectangular cross section, Area = width * layer height.
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Hi Everyone!
Wow! Good replies!
There are actually a lot of things that can influence the Gcode values, but if we stick with the basics and simplest of situations:
100% infill
fixed layer height
user-input extrusion width OR nozzle diameter
filament diameter
(flow multipliers are just arbitrary numbers multiplied by the following equations)
You will find that open-source slicers, like Slic3r, have values computed as such:
Slic3r flow calculations, w = width, h = layer height, D = filament diameter
Where the E-value would be the volume of the path length (cross section area * distance traveled in GCode) divided by the area of the filament diameter (pi*D^2/4)
Cross-section shape is computed is a rectangle with semi-circular ends https://manual.slic3r.org/advanced/flow-math
Another open-source software, MatterControl, has a different formula:
Area extrusion = Nozzle diameter * layer height
E value = diameter*layer height* distance / filament cross sectional area
Depending on the slicer, you will get different extrusion values and different results. In fact, if you do the math with the system of equations, you will find a conversion factor between slic3r and matter control, assuming a fixed (equal) layer height, as:
Nozzle diameter MatterControl = width-height*(1-pi/4)
or rearranging,
extrusion width in slic3r = nozzle diameter diameter Matter Control + h(1-pi/4)
My question stems from one topic:
The E values in the gcode are calculated, and the calculations vary immensely between slicers based on the cross-sectional geometric assumptions used for the deposited, extruded mass. This is an issue with all slicers that utilize GCode. In my opinion, it would offer much more flexibility for advanced users if these E values can be manually entered and not calculated.
So, I will end with this: does anyone know the cross-section assumed by Cura, or any other variables that must be included in the calculations?
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Hello,
I was wondering how Cura computes the E values for the gcodes. What type of cross section does the software assume for the extrudate mass?
Thanks!
Tim
Slic3r flow calculations, w = width, h = layer height, D = filament diameter
Flow Calculations
in UltiMaker Cura
Posted
When you say 'and improved my prints', what were the symptoms? What looked bad before and what is the appearance now that it looks better?
The extrusion width will always be greater than the nozzle diameter, unless the layer height is close to the nozzle diameter. By changing from 0.4 to 0.45 in Cura, you actually changed the path spacing as well as the amount of plastic being pushed into the nozzle. Path spacing = width for the Cura engine.
So I would guess you had too much overlap between adjacent passes. You should also adjust the extrusion multiplier for even better prints, if you want to be super calibrated.