Coast at End

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LePaul
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Coast at End

Post by LePaul » April 20th, 2017, 4:24 pm

Found a good video on this. I have had it off and getting some little blobs Going to try some of his tips

https://youtu.be/WWpdGY0V-gM

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Re: Coast at End

Post by LePaul » April 20th, 2017, 4:41 pm

I'm really curious about Coast at End

I had it off for these test cubes on two different printers

My Ultimaker 2+
IMG_6674.JPG
Ultimaker 2+ Extended
IMG_6673.JPG

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Re: Coast at End

Post by LePaul » April 20th, 2017, 5:19 pm

With Cura 2.5 (Coasting enabled)
IMG_6675.JPG

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Re: Coast at End

Post by LePaul » April 21st, 2017, 4:05 pm

I guess I am a bit stumped on it...I did two of the hub pieces last night ,with coasting off. Came out great! (Pictures coming)

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Re: Coast at End

Post by LePaul » May 4th, 2017, 5:36 pm

Would Coast at End fix these surface lines?
IMG_6821.JPG
IMG_6822.JPG

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Re: Coast at End

Post by Neotko » May 4th, 2017, 6:29 pm

Coasting assumes your nozzle drips even after a retraction. And that amount then is added to the amount of filament extruded (if doesn't drip).

That and more stuff on a future post of 'understanding why prints like that'.

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Re: Coast at End

Post by MTVDNA » May 5th, 2017, 12:05 am

Say what... That might explain why I've been getting terrible blobs in some prints after retractions. :-o


Edit: Are you sure it extrudes extra filament when unretracting to compensate for coasting? Not according to this post on the s3d forum (bottom of the first post).

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Re: Coast at End

Post by Neotko » May 5th, 2017, 2:41 am

Well isn't extra. Is just if filament didn't drip, it assumed it did. So depends. There's a more interesting way to remove blobs, but I don't think it can be used the nirmal way. Using negative restart extrusion -0.05 (max) for objets that don't retract much, works amazing for blobs. But it requires to design the object thinking that it will need two different processes. Ofc... you can separate the infill/top/bottom and perimeters quite easy in s3d and use this trick.

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Re: Coast at End

Post by Neotko » May 5th, 2017, 2:48 am

Ofc ofc. There's also another issue. Related to extrusion force + retraction distance (real) that comes from the amount of torque needed for each movement. But still much to write about that to be definitive.

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Re: Coast at End

Post by nilrog » May 5th, 2017, 5:15 am

I played with this a bit and I could reduce the size of those blobs...but I could not get rid of them completely...and there was a limit when increasing the value didn't improve anything. So to completely get rid of those blobs takes some experimenting and fiddling with more settings :P

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Re: Coast at End

Post by Neotko » May 5th, 2017, 6:06 am

I'll try to explain the problem. but is quite big to get a perfect control of all the issues.

First. Motor fails to repeat the movements with or without Torque. (No missing steps, just moves less under torque)

Coasting assumes filament is 'drop' to fill gaps. This releases pressure of filament flexing inside bowden. But as soon it resumes the material on the nozzle have stay X+ time on the nozzle, getting more and more liquid, viscous and more drippy. When the extrusion is resumed, the more liquid filament can move at more speed, making a Hose Effect. Too much make gaps at end and resuming bigger blobs.

About the motor extrusion being so horrible.
http://hackaday.com/2016/08/29/how-accu ... ng-really/

Check the analysis. And assume that the Extrusion is done under torque and Retraction under Notorque (no friction to move it) = Missing MM everytime it moves. With the ZGE at fast speeds, since everything occurs without delay I could actually see this. With Bowden it 'blurs' a bit and makes it much harder to predict.

The solution...

- Extra Retract Distance Negative. Depends on how much torque the motor needs (fast prints, since slow prints at cooler temps everything changes since the Hose Effect is quite hard to actually see).

But to make it perfect, depends on the temperature. I print everything on my stuff at the same temps speeds, that helps enormously to set a number. With the zge is around -0.02 max. But also I need to split the processes to avoid underextrusion when much retractions occur. This way I can control the outside look (where blobs matter) and the details stay at max retractions on a separate process (texts, little details).

Is perfect? Nope.

Solution? A way overpowered Motor motor like Bondtech. And also, a non-missingsteps-board.

This with bowden is muuuch more complex since the variables increase, but it could be used if one knows his materials.

Also.. As a side note. The Hose effect, is actually really usefull for flexible materials at high speeds. Printing 60mm/s 0.2 layers without taking it as a variable would requiere temperatures so high that the material would degrade releasing toxic stuff on the air.

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Re: Coast at End

Post by LePaul » May 5th, 2017, 9:20 am

That's interesting since I was debating if this string of blobs qualified as Scars on Top Surface . They also point out Extruding too much plastic (and Z-Hop)

I'm printing at 210C with ColorFabb and Ultimaker brand filaments, which I have found print well at this temp (or even a bit higher)

If I was printing too hot, I would expect some pretty melted looking prints. But asides those artifacts on the top surface, they print very nicely.

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Re: Coast at End

Post by Neotko » May 5th, 2017, 10:41 am

Well there's a difference between too hot and accumulation of X temp filament that will flow easier after X time.

Bowden and 2.85 normally do that unless you orint cooler since filament flex inside bowden and that force accumulated goes free when it can. Also maybe you have retractions only when crossing open spaces, that removes retractions inside the object perimeter, and the inside counts as not open spaces, so it doesn't retract.

Top layers, that's why I have change so much stuff on my printers to the point that they ain't anything UM could make.

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Re: Coast at End

Post by LePaul » May 5th, 2017, 12:43 pm

Neotko wrote: Also maybe you have retractions only when crossing open spaces, that removes retractions inside the object perimeter, and the inside counts as not open spaces, so it doesn't retract.
Now that's an interesting comment...I'm at work so no access to S3D at the moment....that must be in the Advanced section?

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Re: Coast at End

Post by Neotko » May 5th, 2017, 12:52 pm

Yea, last tap

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