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Issues with hole sizes.


Frosty1999
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Posted (edited) · Issues with hole sizes.

Hello, I am experiencing an issue with my holes being 0.2 mm smaller than my model needs. I looked through the settings of Cura and noticed the setting Hole Horizontal Expansion. I read about it, and it seemed to be what I needed. However, it is affecting some holes that printed at the correct size such as the rectangular hole through the part. It creates a box the same height as the rounded holes but stops above or below that hole. All my other dimensions are acceptable except the holes going through the sides of the part. The rectangular hole is the same dimensions all the way up. Is there a different setting I should be using?

Horizontal Expansion Question.png

Edited by Frosty1999
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    Posted · Issues with hole sizes.

    You have to realize what the "Hole Horizontal Expansion" setting does, and that Cura is neither magic nor can it read your mind.

     

    Both "Horizontal Expansion" settings only work on the layer level. To understand how they work, you would have to look at a slice layer by layer. The "Horizontal Expansion" setting tries to expand or "grow" each layer (as opposed to  "scale" the layer). Typically the outside gets bigger and holes in the layer get smaller. Scaling would make the holes bigger.

     

    The "Hole Horizontal Expansion" setting applies the same type of expansion on holes, but leaves outside walls as is. And here's where the "not magic" and the "not reading your mind" bit comes in. Cura regards the rectangular void in the layer as a hole. It does not know that you only meant the smaller circular parts. If you would look at one of the layers where the two circular holes in your screenshot seem to affect the hole horizontal expansion, you'll notice that the rectangular area is in contact with the outside wall. As an effect, Cura does not see that section as a (rectangular) hole in those layers so it does not get expanded. Hence the change in hole dimensions.

     

    So what to do in your case, where you want to expand some holes, but not all of them? You could add meshes (either from a support blocker, or another mesh you load) to overlap the holes you want to have expanded, and use the "Per Model Settings" tool to change the Horizontal Hole Expansion setting only where the added model overlaps your original model.

     

    You may also want to look in to the "Slicing Tolerance" setting.

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    Posted · Issues with hole sizes.

    I am not understanding everything from your response. You said that Cura sees the rectangular void as a hole and tries to apply the horizontal expansion to it. If Cura sees that feature as a hole and applies the horizontal expansion to it, why does it not apply it to the whole feature? Are you saying that if we look at it layer by layer, that in the layer where the round holes start, I will technically have two separate bodies making up the rectangular hole around the round holes and then Cura sees that it needs to apply the expansion only in this area? Also, you are suggesting that I load two of the same models and then use horizontal expansion to eliminate any overlap?

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    Posted · Issues with hole sizes.
    On 3/3/2023 at 3:48 PM, Frosty1999 said:

    in the layer where the round holes start, I will technically have two separate bodies

    That is indeed what I am saying. However even if there were just one of the round holes, that layer would still not have a "hole"; A wall that can be reached from the outside by simply following the outside wall is not a hole in Cura's point of view.

     

    On 3/3/2023 at 3:48 PM, Frosty1999 said:

    I load two of the same models

    No, that is not what I meant. You load your model and for example a cylinder that is just slightly bigger than the hole you want to use horizontal expansion on. The exact size of that model is not all that important. Then you use the Per Model Settings tool to change the horizontal (hole) expansion where the two models overlap. So you apply the settings locally.

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