VP and other preload settings

VP and other preload settings

Postby Tinchus2009 » 22 Dec 2018, 15:24

Hi. Im printing with kisslicer everytime I can, it prints really nice once you get the values correct, nice software. Im now trying to use it with PETG (I have had super great results with PLA and ABS so far)
But now I have some questions that arise due to some problems I never had before:
My prints with petg are showing a blob in the areas where the perimter finishes. I think I have calibrated the preload well, but I will re do the calibration later just to be sure. But I wanted to ask some questions:

1.- the vP (mm/s) value, that value is set automatically or I should tune it somehow myself? I habe a bowden setup, bowden is 50 cms long, and the actual value there is 25 mm/s wich somehow sounds low if that value would be a retraction speed. Do I need to tune that value? How?

2.- Aldo Im getting some underextrusion, severe in some areas like in single perimeter support structures. Thing s that same amterial, same printer and basically same setting like speed, temp, etc used with other slicer gives me much better results (with petg), so the only varuable is the preload. Can the preload be causing trpubles like these underextruded areas, or the blobs at the end/start of perimeters?

3.- Im trying to use double extrusion priting : Im not getting a clear picture of what COOL - PURGE setting does (under Printer > extruder hardware settings). In wich area is this "cool purge" done? in the priming tower?

I have atached the project file so yu can see my settings

I was looking in the forum: I found a recent case with a picture showing the exact same blobs as Im haveing: download/file.php?id=1573&mode=view
thaks in advance
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settings.zip
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Re: VP and other preload settings

Postby pjr » 23 Dec 2018, 04:12

I don't print with PET, so I can't really advise on that :(

However, it may be that you need to tune your destring parameters (distance, speed, wipe).

Underextrusion - where? If it's the start or the end of a path, your Preload may be too high.

Cool - purge is for SNMM (single nozzle, multi material) printers (such as Prusa "originals" with MMU), which use only one nozzle and the filament is changed as required. This is the amount of filament that will be "rammed" before being unloaded. The ramming is fast extrusion which cools the melt zone and allows the filament to be unloaded with a tip that can be re-loaded. This occurs on the purge octagon - see settings/support/prime pillar - the last option in that drop-list is the "Purge Octagon".

Peter
Please note: I do not have any affiliation with KISSlicer. Any advices given are offered in good faith. It is your responsibility to ensure that by following my advice you do not suffer or cause injury, damage or loss.
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Re: VP and other preload settings

Postby pjr » 23 Dec 2018, 04:23

I just had a look at your settings.

I think your destring is way too high. When using Preload, destring can be close to zero.

What would I try? Well, maybe reduce destring (3), velDstr (25) and set wipe to zero.

Why? Well the idea is to prevent strings and blobs. This should require only the nozzle "throat"* to be cleared of filament. Destringing too fast will cause separation higher up in the melt zone and will not suck the melted filament back. Including a wipe will have a tendency to suck the melted filament out of the nozzle.

Peter

* the "throat" is the tip of the nozzle and is usually a length of 1.5 to 2 x the nozzle diameter.
Please note: I do not have any affiliation with KISSlicer. Any advices given are offered in good faith. It is your responsibility to ensure that by following my advice you do not suffer or cause injury, damage or loss.
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Re: VP and other preload settings

Postby sinned6915 » 23 Dec 2018, 15:08

i found the Printer Wizard and Material Wizard defaults to give pretty good results and descent prints.

1. Have you confirmed your filament diameter and calibrated your extruder? Calibrate your extruder and leave the flow tweak at 1.0 for now.

2. For comparison, I have a ~75cm bowden, 1.75mm filament, T=240. For my setup, PETG has preload of 1.88 and destring of 0.2. Again, this is my setup. Also, my preload and desting velocities are lower.

3. How short are you loops that you are printing? Is the wipe getting triggered?

4. How did you come up with your seam depth and seam gap settings? I like 1 for Seam Depth and 0.6 for Seam Gap. IIRC, these are in terms of ratios of extrusion width.


sinneD
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Re: VP and other preload settings

Postby Tinchus2009 » 25 Dec 2018, 21:09

ok, I will definitly try what Peter and Sinned recommends .
What I see is that there seems to be different aprouchs regarding dstring (retractions). Some people say I should retract as fast as I can, other say to make it slow, s peter recommends. Actually I was retracting at 70mm/s (I recognized I was seeing damage in the filament). I have already tried peter's recomendation and lowered to 30 mm/s with EXCELENT results in petg (what used to be s stringy print now is really clean, despite petg is know to be stringy).
Still need to check my preload calibration because I still have those artifacts in the prints and underextrusion in small circle geometries.
Im really curious about that 0.2 retraction in a 75 cms bowden tube... knowing the "spring effect" a bowden tube has on the filament, how is it posible that such small retract value means something?
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Re: VP and other preload settings

Postby pjr » 26 Dec 2018, 05:19

I learned a lot about retraction from Michael Hackney's blog : http://www.sublimelayers.com/2016/10/so ... racts.html

Well worth the read...

Peter
Please note: I do not have any affiliation with KISSlicer. Any advices given are offered in good faith. It is your responsibility to ensure that by following my advice you do not suffer or cause injury, damage or loss.
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Re: VP and other preload settings

Postby Tinchus2009 » 26 Dec 2018, 07:45

Super interesting article Peter, thank for shareing it!

I will quote: " PLA is more sensitive to retract/advance speeds than ABS and other materials. My recommendation for PLA is to retract relatively fast (40-50m/s) (and short as per the previous guideline) and advance slower (20-25mm/s). At this time, only KISSlicer has this feature. In other slicers, a reasonable compromise is to retract and advance at 20-25mm/s."

I cant find that configuration. in the material settings, I have the VelDstr value wich applies to both retract and prime, what settings is Mr Hackney taling about for a separate speed for retract and primeing?

Thanks in advance
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Re: VP and other preload settings

Postby pjr » 26 Dec 2018, 09:49

Tinchus2009 wrote:"At this time, only KISSlicer has this feature. In other slicers, a reasonable compromise is to retract and advance at 20-25mm/s."


The article was written some time ago, when KISSlicer did have that feature.

Preload has since been implemented and the feature removed :( although it is on the list of things to be implemented.

Peter
Please note: I do not have any affiliation with KISSlicer. Any advices given are offered in good faith. It is your responsibility to ensure that by following my advice you do not suffer or cause injury, damage or loss.
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Re: VP and other preload settings

Postby Tinchus2009 » 27 Dec 2018, 06:37

Can we use the same preload value in version 1.6 and in 2.X alpha?
The preload speed seems to be set automatically? or we can tune it too?
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