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Combing Setting Does Not Work For Small Holes with Thin Walls


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Posted · Combing Setting Does Not Work For Small Holes with Thin Walls

I have been trying to do a print on an UltiMaker S3 that has small holes, but in every print there is stringing inside the holes. I noticed that the path of the nozzle was going over the holes so I turned on combing and set it to "all", but the nozzle path still travels over the holes (I also tried the other combing options along with other combinations of settings and the result is always the same). I decided to try putting the same file into the Cura LulzBot slicer, and the combing setting turned out to work perfectly in that software. I'm not sure what could be going wrong with the UltiMaker Cura software that would make the combing setting not work since it seems to work very well in the other Cura slicer software.


Below is a picture of the path going over the holes even though combing is set to "all". I also attached the .3mf file in case I have any other settings that look off.



As a note: I tried enlarging the model in the slicer and I noticed that the layers closer to the bottom with more space between the holes did a much better job with combing than the layers toward the top where the space between holes is much smaller. I would still like to print the model with the thinnest possible walls on the top layers though.

UMS3_Stringing Test with Hexagons.3mf

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    Posted · Combing Setting Does Not Work For Small Holes with Thin Walls

    Combing makes it stay out of the printed areas, so holes are fair game.

    A large part of the problem is that it's printing each hexagon separately (the white dots indicate starts, so it would have had to travel to get there):


    But because it's avoiding walls where possible, it's only travelling through the holes as it goes between each hole, because there's no possible path between the end of one and the start of the next one it does which doesn't hit a wall, so it just retracts and takes the direct route.

    Cura slices so that every hole has an outer wall around it, so I'm not sure there's much you can do about it - it's working as intended.

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    Posted · Combing Setting Does Not Work For Small Holes with Thin Walls

    Okay that makes sense, and thanks for the reply. Do you have any advice for how I can make the path of the nozzle avoid going over the holes? If there is no other option, it seems like I'll have to play around with other settings to avoid stringing.


    I've also noticed that if I make the model very large, the combing setting has no issue avoiding the holes. Do you know why it only works when the model is large?



    I also pasted the picture from the Cura LulzBot slicer below on the normal sized model (with very thin walls), and the combing setting works perfectly to avoid the holes which makes me think there is something in the UltiMaker Cura slicer software that causes a different result when there are thin walls. Any thoughts on why that could be happening?


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    Posted · Combing Setting Does Not Work For Small Holes with Thin Walls

    When you make it big there's enough room to generate skin (top/bottom, shown in yellow) between the hexagons which it will create a path through because there's enough room to go through there without hitting any walls.


    Note that if you have Combing Mode set to Not on Outer Surface, Not in Skin or Within Infill it will travel through the hexes to avoid going through the very top and very bottom layer, all skin layers or anything which isn't infill respectively. I usually use Not on Outer Surface because if there's only travels through holes at the very top and bottom layers they're easy to remove and look better than constantly pathing around them.

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