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Inner Hole Diameters constantly to small


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Posted · Inner Hole Diameters constantly to small

In another thread I stumbled over this:

 

@GregValiant mentioned: 

Quote

Holes create a special problem.  The nozzle drags the plastic in a circle and the plastic wants to cut corners so it pulls towards the center making an ID smaller  You don't notice it as much on an OD because usually there is an inner wall to act as a dam to keep the plastic outboard.  How much it pulls to the middle is affected by a lot of things.  The phenomenon is known as the Gr5 Snot Factor after it's discoverer who had a runny nose at the time.

 

His proposal had been to use "Hole Horizontal Expansion" to compensate for this phenomenon, which is nor useful, as soon as a lot of different hole diameters appear in a single print.

 

Wouldn't it be a solution to print inner diameters very very slowly? This could be another approach feasable with CURA...

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    Posted · Inner Hole Diameters constantly to small

    "The thing to remember is that there is no spoon" - from The Matrix

    Philosophy in the morning...

    The real problem with Hole Horizontal Expansion isn't diameters or bores because there are never any diameters or bores.  What we have are certain features that are comprised of a series of short line segments that our human brains see as diameters or bores.  The problem is how to get a piece of software to recognize that a particular collection of short line segments constitutes a bore as opposed to some other shape.

    The problem rests squarely in the laps of a bunch of dead Greeks.  The current world record for the calculation of PI is 31 trillion decimal places and so there are always line segments, they just keep getting shorter.  How should a swaged hole (even a triangle) be handled?  There are 3 facets.  Is it a triangle(?) or is it the roughest possible approximation of a circle in a low resolution STL file?  I heard that Pythagoras personally told @kmanstudios the answer, but Kman doesn't want to admit that.

     

    This is one of those things that the user must keep in mind when using HHE.  The user must tell Cura what a hole is.

     

    I cranked up the HHE to 3mm on the gear below to show what Cura does.  The gaps between the spokes are "holes" and the spokes pretty much disappear as does the hub as the 4mm bore grew to 10mm.

     

    Untitled.thumb.png.c89dd534327307cc92a06b1d289f89cc.png

     

    Here is the same gear with HHE set to 0, but with a Mesh Modifier in place over the bore and configured as a Cutting Mesh with HHE set to +1.  I haven't actually defined what a hole is, but I've told Cura to treat this particular group of short line segments in a different way.  I have placed the cutting mesh so the nut cavity on the bottom is not affected.  You could alter the print speed in the same manner for this particular area as well.  That wouldn't be as precise as telling Cura to make the feature a specific amount larger.

     

    Untitled1.thumb.png.8cec7c8475795521553d69ae6763dbe8.png

     

    This all leads to the horrible statement - "It might look like a hole but its snot."

    I'm going to have another cup of coffee now.  There will be a spoon to stir it.

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    Posted (edited) · Inner Hole Diameters constantly to small
    2 hours ago, GregValiant said:

    I heard that Pythagoras personally told @kmanstudios the answer, but Kman doesn't want to admit that.

    Yes, I am that old. And no, I do not kiss and tell 😛 

     

     

      

    2 hours ago, GregValiant said:

    I'm going to have another cup of coffee now.  There will be a spoon to stir it.

    Nv3.gif

    Edited by kmanstudios
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    Posted · Inner Hole Diameters constantly to small

    a² + b² = c²

    Entropy always increases.

    If you let go of an apple there is some slight chance it will go up.

     

    Going back even further, it has always been about how you look at things.

    perspective.thumb.jpg.d3a6ea0e5247d8876177ad587b2aba4a.jpg

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