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Hum... What's combing?

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Posted · Hum... What's combing?

There are quite a few threads mentioning "combing". I did some searches but couldn't find a clear explanation aimed at the beginner that I am to say what it is, when and how to use it. Would any of the good guys out there be able to take a few minutes to explain?

Thanks!

 

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Posted · Hum... What's combing?

I don't know if I am a good guy, but I hope, I'm not a bad guy... ;)

Combing is the opposite to standard travelling where filament is retracted, the head moved in a straight line and filament primed. With combing enabled, moves between points which belong to the same continuous part of the layer on which the travel is executed follow the contours of this continuous part instead of a straight line and no retraction / priming of the filament is performed.

The consequences of combing are lines that cross horizontal surfaces and look ugly.

 

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Posted · Hum... What's combing?

Stated in another way it tries to avoid crossing over perimeters of the part so that travel moves are performed over infill to avoid defects on the outside surface.

 

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Posted · Hum... What's combing?

For layers with hatch like infil, combing is no big deal and usually saves time because you skip a retraction step. But for bottom and top layers combing can make an ugly scar. So for example if you are printing a cell phone case where you want the bottom layer to be the best layer, then you probably won't combing off. For 90% of my prints I have combing on.

 

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Posted · Hum... What's combing?

Even on interior layers, combing as implemented in Cura is a bad idea, as it doesn't perform retraction, and that can result in the head oozing as it moves, especially as each time the head crosses a line of infill it can tend to pull our some plastic. You can also get some long moves (e.g., all the way around the curve of a 'C' shaped object when moving from one side of the opening to the other). This can result in the head being empty when it starts printing the perimeter again, with resultant under-extrusion effects.

While the 'not crossing boundaries' effect is a good thing, in principle, the 'not retracting' is a bad thing. For that reason, I never ever enable combing on the UM2.

 

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Posted · Hum... What's combing?

Good points; this discussion has been very useful for me. The description of combing in Cura had left me wondering:

"Combing is the act of avoiding holes in the print for the head to travel over. If combing is disabled the printer head moves straight from the start point to the end point and it will always retract."

 

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Posted · Hum... What's combing?

Cura thinks of each layer as a separate entity of closed shapes with holes in them or gaps between the shapes. So a hole in this case is an area of a given layer that is considered *not* infill.

 

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