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jean-baptiste

Minimal speed & print all at once

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Hi everybody !

I have see today a problem on the printing with more than one object to print (mode print all ar once, I don't will print one at time ;) )

Cura don't take the mesure of the surface on the piece but all the surface of all the piece at the same stage. So the minimum speed doesn't really work ;)

Jean-Baptiste

 

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The full time for the full layer is calculated, if this is shorter then the minimal layer time, the speed is slowed down so the layer meets the minimal layer time. But, it's never slowed down more then the minimal speed. (which you generally not hit unless you have a few mm2 of area). If this happens, the "cool lift head" feature can trigger if this is enabled, which lifts the head to make up for the time not reached by the minimal layer time.

https://github.com/Ultimaker/CuraEngine/blob/master/src/gcodeExport.cpp#L543

 

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That's exactly right :)

 

The trouble is when you print a lot of parts with small area, It takes account of all areas and not just the part that is currently printing I feel. In the end it does not slow down while in this case it for these small areas.

 

Do you understang what I say ?

 

Thanks a lot Daid :)

 

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I think I understand your problem:

When you have small, separated areas (I'm calling them "islands") in a layer, and particularly if they are at the edges of the model (and not in the center), then you'll have the problem that these islands can be printed too quickly.

This wouldn't be an issue except when the small island is actually the last thing being printed on the current layer, and then the first one one the next layer. In that case, the printhead remains on this island for a long time and melts it up.

printing small areas 1

 

Here I have several islands. The one in the bottom right is the problem: It's the last area being printed on this layer. Then, the printhead moves to the next layer but prints the exact same island again (because it's the shortest way for the printhead and therefore logical to start with it).

For some materials (especially Colorfabb XT), this can be a big problem because these two layers alone will already make the extruded plastic expand because of the excessive heating. The expanded part will cause problems on the next layer. It doesn't matter if this "printing the same island twice in a row" happens repeatedly or only once - once is already enough to cause problems for some printing materials.

 

My workaround for this problem is to simply add another island to move the problem away from my model and to a dummy part:

 

printing small areas 2

(I'd need another column on the bottom left as well, just quickly made the picture as a reference...)

You can see from the blue lines that my part's bottom right island is now ok. The layer change now happens at the "support" column.

A better solution imho would be for Cura to forbid printing the same island twice when changing layers (provided there is more than one island of course). Maybe add a size rule so that the rule only applies for smaller than "X mm2" islands.

Or maybe you could just force the printhead to move at least "X mm" away from the current position after a layer change, before it starts printing again. 10 mm should be enough in this case.

/edit:

I know I don't have multiple parts, but having a single part with multiple islands is in fact the same thing as having multiple parts... I suppose Cura doesn't differentiate between these two things either when in "print all at once" mode.

 

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If you like the quality at lower print speeds versus 100mm/sec then maybe you should print the entire part at the lower print speed.

If you only want to improve quality on the top portion of the part then consider using "TweakAtZ" which allows you to slow down the speed at a given layer height (Z).

The "minimal layer time" feature is only to improve *cooling*.

 

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