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Nozzle drag

Posted by NelsonRap 
Re: Nozzle drag
June 29, 2011 05:25PM
I think this is what you are looking for:
[www.mendel-parts.com]
Re: Nozzle drag
June 29, 2011 07:00PM
ahmetcemturan Wrote:
-------------------------------------------------------
> I think this is what you are looking for:
> [www.mendel-parts.com]
> opic.php?f=37&t=256


Thanks Ahmet, exactly what I was looking for. Btw, çok saol. Burda başka bir Türk gördüğüme sevindim. (that was a bit of foreign speak...)
Re: Nozzle drag
June 29, 2011 07:09PM
After reading up on this a bit, here is my plan of action for getting the amount of plastic extruded to a good point, with skeinforge 41 and using repsnapper to run the machine:

1. Set my e_steps in firmware so 100 mm of plastic goes into the extruder when given a command of E100. Never change it again once set.
2. Set feedrate and flowrate equal in the speed tab. This way when you want to speed up you just change these two values and everything else should match up.
3. Set skeinforge for width over thickness(W.O.T.) to the desired value (I want 1.5, so my filament should be 0.3mm high by 0.45mm wide when extruding.)
4. Run a test print, and measure what the actual W.O.T. is.
5. Adjust the packing density over several test prints to experimentally arrive at the correct value.

It seems there are many ways to arrive at the right settings, I will try this approach and see if I get any measure of success out of it.

Also, are there recommended values for W.O.T. for a given extruder nozzle size? I can imagine there must be an upper limit to what is possible.


Germanicus
Re: Nozzle drag
June 29, 2011 07:51PM
How are you measuring the W.O.T after the print is finished?

I have my extruder sucking in 100mm when given the command and don't want to mess with the E steps now that is set, I guess I will play with the W.O.T and see what happens and or if that doesn't work possibly the packing density.


__________________________________________________________________________
Experimenting in 3D in New Zealand
Re: Nozzle drag
June 29, 2011 08:50PM
I usually stop the print before it is finished so I can measure the filament. I'm going to try a W.O.T. test soon to see if skeinforge is adjusting the extruder output based on it or not. I have a feeling that it is not adjusting it, or maybe there is an optimal W.O.T. for my 0.35mm extruder nozzle.


Germanicus
Re: Nozzle drag
June 29, 2011 09:31PM
NelsonRap Wrote:
-------------------------------------------------------
> How are you measuring the W.O.T after the print is
> finished?

Print single wall test pieces and use callipers to measure it.


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Re: Nozzle drag
June 29, 2011 10:16PM
Andrew Diehl Wrote:
-------------------------------------------------------
> nophead Wrote:
> --------------------------------------------------
> -----
> > It spaces them further apart but the volumetric
> > version of SF is supposed to calculate the
> correct
> > volume of plastic from the height and the width
> of
> > the print roads, so it shouldn't affect the
> > overfill from SF40 onwards.
>
> I was under that impression as well. I just ran
> some simulations in SF which proved me wrong.
> Changing the infill width over thickness only
> changes spacing between lines and not the volume
> extruded per line.

I just ran a couple of test prints and can confirm that the volume of plastic does seem to change when the W.O.T. is changed in skeinforge. I'm looking into using a low value like 1.2 or 1.3 for the perimeter and high value like 1.9 for the infill.

I ran a print with W.O.T. at 1.1, and another with it at 1.9 and both showed similar contact between individual lines and no excess plastic on the top. Photos are up on my blog.

Edited 1 time(s). Last edit at 06/29/2011 10:38PM by germanicus.


Germanicus
Re: Nozzle drag
June 29, 2011 10:38PM
Just to clarify since I just noticed in

Carve I have layer thickness 0.4 and Perimeter width over thickness 1.8

in Bottom I have Additional height over layer thickness 0.4

in Fill I have Infill width over thickness 1.5


__________________________________________________________________________
Experimenting in 3D in New Zealand
Re: Nozzle drag
June 30, 2011 02:36AM
Basic formula: to get it right:
Extruding too much or too few for your nozzle diameter not taken into account:
Set your layerheight (LH) and Perimeter width over thickness ratio (PWR).
Multiply LH and PWR. That gives you your extrusion width in mm. (LH x PWR =EW)

Now calculate LH x EW = FCS (Fill x-section). that gives you the crosssection for the infill. This is the amount that SF calculates for volumetric dimension... It is the right amount for the infill... BUT: The primeter gets way too much extrudate this way. The volume for the perimeter would be:
LH/2 x EW/2 x 3.14 = PCS (Perimeter X-section).
Now get the ratio of PCS to FCS. (PCS / FCS = VRR (Volumetric reduction ratio..)

Set in SF- Speed: both extrusion and fill rate to same value. (50-50 maybe)
Set in Speed perimeter feedrate over operating feedrate ( to maybe 0.5 (so your perimeter is extruded slower and you get a better finish))
Now for the perimeter flowrate over operating flowrate multiply the PFROOFR with the VRR.. (Here 0.5 x VRR,)
Set it there...

You should be done...

You get good results if your nozzle x section ( (nozzle diameter/2)^2 x 3.14) is slightly or the same as your PCS...

Enjoy nice prints...


www.reprapfordummies.net
IRC: #reprap on freenode.net (Action68)
[github.com]
Re: Nozzle drag
June 30, 2011 02:36PM
Thanks
just done a quick calculation on what is already set up and I got 0.784

LH0.4*PWR1.8= 7.2

LH0.4*EW7.2= 2.88

LH/2*EW/2*3.14
0.4/2*7.2/2*3.14= 2.2608

PCS/FCS
2.2608/2.88=0.784

so going with a perimeter feedrate of 0.5 I get
0.5*VRR
0.5*0.784= 0.392

I have a 0.5 nozzle

If I have read this correctly I would set the perimeter flow rate to 0.39 then?

Edited 2 time(s). Last edit at 06/30/2011 03:32PM by NelsonRap.


__________________________________________________________________________
Experimenting in 3D in New Zealand
Re: Nozzle drag
June 30, 2011 05:03PM
Am i correct in LH0.4*PWR1.8=0.72 ?
I also think there is something wrong with that math because the resulted VRR seems to be constant: to quote: [LH x EW = FCS] and [LH/2 x EW/2 x 3.14] therefore PCS = FCS * 3.14 / 4.
But maybe i just dont understand it all.
FCS seems like layer_height^2 * aspect_ratio, which simplified looks like the area of the given W/H rectangle.
PCS dunno what it can be like that, i see a pi(), i see a division by 2 so maybe it was intended to be the area of a circle like = pi*R^2 where R=diameter/2. But like [LH/2 x EW/2 x 3.14], first part is 1/4 of the W/H rectangle and that multiplied with pi doesnt get me anywhere.

I think the writer was somewhat in a hurry and skipped something. I was working at a newspaper long time ago, and it was a habbit after one writes an article, some1 who has no clue about it reads it to give it "clear head". Its an interesting term which means the writer is involved in the stuff and may consider some parts self understood. Whereas some1 who has no clue about what is it, has its head clear - and will imediatelly point any areas that are unclear, or grey, or any curiosity that was not satisfied. I believe the above is a good example, though maybe i just overlooked something and its just me who doesnt understands. I found i understood this better when i was reading it [hydraraptor.blogspot.com] - i think its more or less around this topic.
Re: Nozzle drag
June 30, 2011 05:04PM
The first line gives you 0.72mm.
Second line 0.288 mm2
Third 0.226 mm2
fourth : correct 0.785

Your result is correct:
Re: Nozzle drag
June 30, 2011 05:16PM
ahmetcemturan Wrote:
-------------------------------------------------------
> The first line gives you 0.72mm.
> Second line 0.288 mm2
> Third 0.226 mm2
> fourth : correct 0.785
>
> Your result is correct:


So do I need to adjust to get the result that is currently 0.785 to be almost the same as my nozzle at 0.5?

I think that's what your saying


__________________________________________________________________________
Experimenting in 3D in New Zealand
Re: Nozzle drag
June 30, 2011 06:21PM
@Nelsonrap: Do you have .5 for P-feed and 0.785 for the P-flow in speed?
Anyway you need to set it 0.5 and 0.39

This way you can get correct dimensions and watertight perimeters and full fills...

@Noobman: Nopheads blog post adresses the same issue.. He makes a few calculations different than I but the idea is the same...
SF calculates the extrusion volume as a rectangle of width and layer height. This works fine for the infill where there are lines next to each other and you can cram the plastic into rectangle shape to make it "watertight"
Unfortunately during print when you extrude perimeter first you have to rely on the surface tension and the viscosity of the extrudate to achieve any shape. (Without the surface tension and the high viscosity of molten filament the plastic would flow like water...)
What results is an oval. (sometimes an ellipse but oval is more useful in this place.. )
The area of an oval is height/2*width/2*pi... Thats what we use to get the ratio...
The VRR is constant as long as the shape (layer height/extrusionwidth) remains the same.. Basically we try to calculate the missing part in the rounded corners..

"FCS seems like layer_height^2 * aspect_ratio, which simplified looks like the area of the given W/H rectangle. "
FCS is calculated by SF as a rectangle..Its the base for the volumetric thing. (Although I changed it in my own version of SF to take the perimeter as base and I play with the infil...)

And you are right... I was in a hurry but dont think that I skipped something... And thank god this is not a nespaper as readers can actulally ask questions if they dont understand anything.


www.reprapfordummies.net
IRC: #reprap on freenode.net (Action68)
[github.com]
Re: Nozzle drag
July 01, 2011 02:21AM
Yep so have changed the settings in speed to match they are 0.5 and 0.39 and in carve I have layer thickness 0.4 and Perimeter width over thickness of 1.8

in bottom I have a Height over layer of 0.4 and in fill I have Infill width over thickness of 1.5

Hopefully get to test so point over the weekend


__________________________________________________________________________
Experimenting in 3D in New Zealand
Re: Nozzle drag
July 01, 2011 11:02AM
1) VRR meaning
Just as mathematics go, if the input relations are:
[FCS=LH x EW] and [PCS=LH/2 x EW/2 x 3.14] therefore PCS = (FCS/4) * 3.14 therefore VRR = PCS/FCS = 3.14 / 4 = 0.7850 (constant)
Bottom line, i cant see the point to calculate VRR ever, since all variables in the formula cancel each other out, the VRR remains always constant regardless of inputs.
Could say from the start that VRR = a quarter of pi, tho i dont see its relevance for the sf math.

2) PCS representation
I also honestly dont understand which area PCS is meant to represent either. [PCS=LH/2 x EW/2 x 3.14]. It feels like:
- either is 1/4 that rectangle*pi
- or its an attempt to a circular area (pi*R^2) where R^2 is meant like the product of LH&EW?
In either case i cant figure where does it come from. Maybe i dont have enough imagination tho.
Re: Nozzle drag
July 01, 2011 12:12PM
Hi NoobMan,
1)I will recheck it. Even better if we have a constant ratio. But it also can be that I wrote down it here wrong...
2) [www.ehow.com]


www.reprapfordummies.net
IRC: #reprap on freenode.net (Action68)
[github.com]
Re: Nozzle drag
July 01, 2011 01:36PM
Nice, thanks for the quick reply. It seems i can use either more 3d imagination or intuition. So i can see it now, its the oval inside rectangle - didnt crossed to me that way.
Then ratio of VRR is basically the representation between the rectangle and the oval it can fit inside it, or other way the empty space that remains.
And then ofc it makes total sense to be constant, because regardless what dimensions the rectangle has, it can fit a directly proportional oval inside it, and the ratio of oval/rectangle or empty_space/rectangle are always the same - regardless of the rectangle size.
Re: Nozzle drag
July 01, 2011 02:03PM
The problem is it is not an oval because where it touches the nozzle and the layer below it is flat. This gets more different from an oval as the width over height gets bigger. I think the model I produced is more accurate in predicting how much volume is needed to make the outline the correct width.


[www.hydraraptor.blogspot.com]
Re: Nozzle drag
July 01, 2011 03:10PM
Hi Nophead,
I experimented with a few crossections actually but found that as long as you dont overstep a certain width height ratio the x-sections are very similar to the oval calculation. So just stuck with the simplest calculation...
Also your description (at least to me) is as if it somhow approaches the topic from the result...
I prefer to see how Sf calculates fill. (as a rectangle) then calculate the error ratio to the Oval... Gives very good prints...

NoobMan: You are absolutely correct.. VRR is constant. Thanks for seeing that the error ratio is constant. If a few users could confirm that they get good prints with that ratio it could be calculated in SF automatically...
Re: Nozzle drag
July 01, 2011 04:19PM
NelsonRap Wrote:
-------------------------------------------------------
> Yep so have changed the settings in speed to match
> they are 0.5 and 0.39 and in carve I have layer
> thickness 0.4 and Perimeter width over thickness
> of 1.8
>
> in bottom I have a Height over layer of 0.4 and in
> fill I have Infill width over thickness of 1.5
>
> Hopefully get to test so point over the weekend

Can you confirm what I have ended up with here please?


__________________________________________________________________________
Experimenting in 3D in New Zealand
Re: Nozzle drag
July 01, 2011 05:37PM
Yes, 0.5 x 0.785 = 0.3925
Re: Nozzle drag
July 01, 2011 05:42PM
And is my fill and height over layer in bottom right to work with those settings?

Thanks


__________________________________________________________________________
Experimenting in 3D in New Zealand
Re: Nozzle drag
July 02, 2011 03:12AM
The bottom settings affect the first layer only. Not so important if you dont have a perfect level bed...
You should have it at 0.5. This way the exit of nozzle will be exactly above your Extrusion (Layer thickness = 0.5 >> Z position 0.5)
This is only valid of course if you have set up your Z-home to be exactly over (touching/barely touching) your printbed.
If you have left some gap for safety (e.g 0.2mm) You should set that in Altitude. Set it to a negative value (-0.2 if your Z-home is 0.2mm above the bed). G-code will be generated for Z0.3. As you have already 0.2 gap beforehand, your nozzletip will now be at the correct position for extrusion.

Note that there is also the setting under RAFT: operating nozzle lift over layer thickness (ratio). I have this one set to 0.5 so it does not affect my first layer height. And as far as I understand it has the same effect as the Additional heigt over layer thickness in BOTTOM.


www.reprapfordummies.net
IRC: #reprap on freenode.net (Action68)
[github.com]
Re: Nozzle drag
July 02, 2011 07:11AM
In SF 40 and 41, you set the flow rate equal to the feed rate and you set the diameter of you feed in the dimensions option to the measured diameter of your feed. If you have set your E steps per mm in the firmware to the calculated value for your extruder, then you just need to adjust the Filament Packing Density Ratio in dimensions to get the infill to come out right. SF does the volumetric calculations for you so that if you later change your layer thickness, perimeter fill over thickness ratio, or infill width over thickness ratio, it adjusts the flowrate accordingly so you still get properly filled objects.

If you don't have the correct feed diameter, then the calculations in SF will be off and your objects won't be properly filled. Even if you've carefully measured and entered the correct diameter, if your feed quality is not good and the diameter varies with length, then your extruded filament will also vary proportionately and your print quality will suffer.
Re: Nozzle drag
July 02, 2011 08:38AM
ahmetcemturan Wrote:
-------------------------------------------------------
> This is only valid of course if you have set up
> your Z-home to be exactly over (touching/barely
> touching) your printbed.
> If you have left some gap for safety (e.g 0.2mm)
> You should set that in Altitude. Set it to a
> negative value (-0.2 if your Z-home is 0.2mm above
> the bed). G-code will be generated for Z0.3. As
> you have already 0.2 gap beforehand, your
> nozzletip will now be at the correct position for
> extrusion.
>

I accomplish the same thing by doing a G92 Z0.2 after the G28 to account for the safety margin in start.gcode.
Re: Nozzle drag
July 02, 2011 01:44PM
You use a workaround for something that is implemented already? smiling smiley
Re: Nozzle drag
July 02, 2011 01:59PM
I use the same method as ahmetcemturan but with the bed height at 0.1 mm with z=0 so I have altitude set to -0.1. This is easily accomplished by using a post it note or a piece of printer paper as a feeler gauge which is very close to 0.1 mm. I just place paper under the nozzle, zero the bed and then pull on the paper. If I can't move it, then increase the height by raising the endstop. If it's too loose, then I lower the endstop. Then rezero the z-axis and repeat until it's right. I do all this with the nozzle and the bed at operating temperature.
Re: Nozzle drag
July 02, 2011 03:09PM
ahmetcemturan Wrote:
-------------------------------------------------------
> You use a workaround for something that is
> implemented already? smiling smiley


The difference is that I can adjust the first layer with one edit of the gcode without recrafting the stl. Zero height of the Z axis is a machine parameter, why would I have skeinforge compensate for it when G92 is designed for that long before your feature was implementated.
Re: Nozzle drag
July 02, 2011 04:17PM
brnrd Wrote:
-------------------------------------------------------
> In SF 40 and 41, you set the flow rate equal to
> the feed rate and you set the diameter of you feed
> in the dimensions option to the measured diameter
> of your feed. If you have set your E steps per mm
> in the firmware to the calculated value for your
> extruder, then you just need to adjust the
> Filament Packing Density Ratio in dimensions to
> get the infill to come out right. SF does the
> volumetric calculations for you so that if you
> later change your layer thickness, perimeter fill
> over thickness ratio, or infill width over
> thickness ratio, it adjusts the flowrate
> accordingly so you still get properly filled
> objects.
>
> If you don't have the correct feed diameter, then
> the calculations in SF will be off and your
> objects won't be properly filled. Even if you've
> carefully measured and entered the correct
> diameter, if your feed quality is not good and the
> diameter varies with length, then your extruded
> filament will also vary proportionately and your
> print quality will suffer.


So if the filament packing density is reduced it will use less material on the fill and on the perimeter? It is set as 1 as the default setting by the looks of it


__________________________________________________________________________
Experimenting in 3D in New Zealand
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