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daoust

Printing thin wall

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Hi,  I m new to this forum and I use cura 3.2 for slicing my 3d project.

 

I created a calibration design for my printer.  My goal was to calibrate the flow of my extruder by printing a wall the same thinckness of my layer width (0.6mm)and nozzle width(0.6mm).  When slicing my parts,  the 0.6mm wall is not showing in the slicer so I enable the function,  printing thin wall ,  now I have my calibration wall but it look strange

 

My nozzle is 0.6mm

My setting in cura 3.2

Nozzle size is 0.6mm

Layer height 0.2

Initial layer height 0.3

Line width 0.6

Infill line width 0.6

 

The stl file was done with solidworks and also from cura with solidworks pligins

 

What can be my propleme

15238378305871450210646.jpg

1523838116767452287349.jpg

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Hello @daoust, sorry but you have hit a big problem with Cura that it doesn't make a good job of thin walls. The problem boils down to the fact that all walls have to be printed as a pair of lines and not just a single line. Cura tries to make amends by providing "wall overlap compensation" which makes a second wall that runs close to a first wall thinner so as to reduce the overall width but, unfortunately, the overlap compensation has many bugs and is not guaranteed to make a good job. It remains a problem area.

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So if,  I double the thickness of my wall from 0.6 to 1.2mm cura should be able to deal with it?  I  will give a try.  I have calibrated my e step on my printer and my filament diameter and now when I print some parts and my flow is at 100%  ,  my nozzle will grind the top surface when printing.  So I was pointed out that it was overextrusion.  From that point I realise that even if the extruder is well calibrated and the filament diameter was set properly,  I still need to calibrate for the density of the filament by setting the flow to a lower value .   

 

So if I print a thin wall of a set value like 1.2mm with a 0.6 nozzle and adjust the flow untill I really print 1.20mm,  is it a good way for calibrating my flow%?

 

I have saw some trying to adjust by printing a small cube,  but I don t  belive that way is good because of the plastic retraction .

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If your "line width" is 0.6mm and your wall is 1.2mm it will do two passes next to each other and extrude the exact correct amount to make a 1.2mm wall.  No flow calibration necessary.  

 

The best way to calibrate your extruder is to extrude 100mm with no load and make sure the filament really moves that far.  If you have a bowden printer like an utimaker then start with the filament half way down the tube so there is no load.  If your extruder is only a few mm from the hot end then extrude very very slowly.  Or take the hot end apart so the filament isn't slowed by the hot end (maybe remove the nozzle?).

 

You can use the feature "print thin walls".  I use this all the time and it works pretty well but you might get some underextrusion right after.  This will allow you to go down to a wall width about the same as line width.  I think you can print a 0.6mm wall with a 0.6mm line width but barely.  If you really need to print 0.6mm wall with 0.6mm nozzle then I recommend you enable "print thin walls" and set the line width to around 0.5mm or 0.55mm.  This works quite well.  I did this exact thing recently.

 

It will extrude 0.5mm the first pass on the wall and on the second pass it will extrude only enough for the remaining .1mm (and move the nozzle just .1mm over to the side).  This works great except when it starts extruding a non-wall it will underextrude for a short period of time while it builds pressure back up.

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My extruder is calibrated that way and I still have some overextrusion even if my filament diameter is set at the real diameter.  So I need to play with the flow setting to reduce the overextrusion and I belive it because the density of the filament is diferent from on to another.  So by printing a thin wall,  I wish to set my flow corectly.  If you go back on top of the discution,  I explain my goal by printing a thin wall.

 

Thank you

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Right.  Got it now.

 

A third way to calibrate extrusion is print some "spaghetti" and then weight it.  e.g. print 100mm of filament and weight it.  Versus cutting 100mm of raw filament and weighing that also.

 

Note that most extruders tend to slip about 10% so "normal" printing should underextrude by 10%.  That seems just wrong to me but that's the way it is.  It's not that the extruder motor is slipping - it's that there is enough pressure on the filament that the diamond shaped holes in the filament are positioned closer together than the diamonds on the feeder.  Because the filament is slipping or compressing or something.  By typically 10%.

 

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My printer is a creality cr-10s (bowden setup)  and I install a bondtech bmg extruder with a capricorn xs tube.   When calibrating my filament,  i ask for 100mm with my octoprint and it gave me exactly 100mm at 100% flow from my octoprint.  Octoprint works with a older cura slicer.  When printing  the benchy at 100% flow sliced on cura 3.2. ,  I have overextrusion .  My nozzle grind the print surface and I saw petg plastic filament that is release from the grinding (touching) stick to the nozzle. That s why I belive even if my extruder is well calibrated,  I still need to adjust my flow setting or maybe I miss something here.  I also belive that some filament will not have the same density that why I belive that It can be set with reducing the flow in my case.

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9 hours ago, gr5 said:

...  Because the filament is slipping or compressing or something.  By typically 10%.

 

I once looked at the indents in the filament under a microscope. If the feeder wheel has square "pyramids" on it, the pits these pyramids leave in the filament get deformed (stretched) into diamonds-shaped pits instead of squares, in the feeding direction, due to the high force exerted on them. You might call it a sort of deformation, or "pit-stretching",or "partial slipping" indeed, but without grinding yet. Similar to car tires partially slipping, and starting to make sound, when braking hard but without locking the wheels up yet. The result is that the feeder wheel turns a little bit faster than the filament, due to this stretching-deformation of the little pits.

 

I also guess this is why flexible filament needs a higher "flow rate" percentage than hard filament like PLA, to get the same correct extrusion? To compensate for more stretching of the pits?

 

If you would calibrate the feeder with nozzle absent (and thus with very little resistance), the result would be different from with nozzle present (and thus higher resistance). Also, higher and lower printing temperatures, and higher and lower printing speeds (and thus higher and lower required forces to push the filament through the nozzle) would have an effect.

 

This might actually be a good test: extrude 100mm of filament (=defined as 100mm), both with and without any resistance, and measure how much difference there is?

 

(But of course there could still be other causes for deviations.)

 

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2 hours ago, geert_2 said:

This might actually be a good test: extrude 100mm of filament (=defined as 100mm), both with and without any resistance, and measure how much difference there is?

@geert_2 Actually, Illuminarti has done this test at multiple temperatures and speeds through a 0.4mm nozzle and he weighted the resulting "spaghetti" and this is what he discovered:

 

The important graph:

https://public.tableau.com/profile/illuminarti#!/vizhome/ExtrusionRates/Sheet1

 

And the rest of the article:

http://www.extrudable.me/2013/04/18/exploring-extrusion-variability-and-limits/

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I have allways use octoprint ti extrued 100mm od plastic fir my tunning,  is there a easy way to do it with cura?   Is it posible that octoprint don t have the same results as cura???

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