Hulling a concave object

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Hulling a concave object

tjhowse
Hi All,

I've designed a wing with variable profile. I built it up out of thin slices of incrementally different wing profiles and union()'d them together. However when I slice (with slic3r) with two top layers, two bottom layers and 10% infill, I get a nearly solid print. I suspect this is because the flat faces of the wing slices are see as valid geometry and must be supported and laid down.

Is there a good way of taking only the surface of a shape that is comprised of many smaller shapes? Hull() would work if there weren't concave sections of the wing. My current hack is to subtract the wing from a big cube, then subtract the resulting cube from another cube of the same size, leaving a solid wing sans slices.

Anyone got a more elegant solution?

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Re: Hulling a concave object

nophead
Have a look at how 3D knots are drawn here: http://kitwallace.tumblr.com/post/74713917178/openscad-revisited. Basically it makes a list of 2D slices and creates a mesh to join them using recursive functions to make lists.

On 24 September 2014 22:48, tjhowse <[hidden email]> wrote:
Hi All,

I've designed a wing with variable profile. I built it up out of thin slices of incrementally different wing profiles and union()'d them together. However when I slice (with slic3r) with two top layers, two bottom layers and 10% infill, I get a nearly solid print. I suspect this is because the flat faces of the wing slices are see as valid geometry and must be supported and laid down.

Is there a good way of taking only the surface of a shape that is comprised of many smaller shapes? Hull() would work if there weren't concave sections of the wing. My current hack is to subtract the wing from a big cube, then subtract the resulting cube from another cube of the same size, leaving a solid wing sans slices.

Anyone got a more elegant solution?

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Re: Hulling a concave object

kintel
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In reply to this post by tjhowse
On Sep 24, 2014, at 17:48 PM, tjhowse <[hidden email]> wrote:

> Is there a good way of taking only the surface of a shape that is comprised of many smaller shapes? Hull() would work if there weren't concave sections of the wing. My current hack is to subtract the wing from a big cube, then subtract the resulting cube from another cube of the same size, leaving a solid wing sans slices.
>
> Anyone got a more elegant solution?

Am I correct in my understanding that you have one solid volume which contains internal cavities, and you want to remove the internal cavities, leaving only the outer shell?

 -Marius

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Re: Hulling a concave object

tjhowse
@nophead: I'll look into that when I get home. I might have to un-blackbox the airfoil generator I'm using: http://www.thingiverse.com/thing:14179

@Marius: Not internal cavities, but internal coincident faces that shouldn't exist.

On 25 September 2014 08:07, Marius Kintel <[hidden email]> wrote:
On Sep 24, 2014, at 17:48 PM, tjhowse <[hidden email]> wrote:

> Is there a good way of taking only the surface of a shape that is comprised of many smaller shapes? Hull() would work if there weren't concave sections of the wing. My current hack is to subtract the wing from a big cube, then subtract the resulting cube from another cube of the same size, leaving a solid wing sans slices.
>
> Anyone got a more elegant solution?

Am I correct in my understanding that you have one solid volume which contains internal cavities, and you want to remove the internal cavities, leaving only the outer shell?

 -Marius

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Re: Hulling a concave object

MichaelAtOz
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Interesting...The Thing, F5 produces a 3D wing section, F6 produces a 2D airfoil profile.

It uses polygon, not polyhedron.
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Re: Hulling a concave object

MichaelAtOz
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OK, I see, it is 1 unit high, as in the F5 simulated 2D view...
Admin - email* me if you need anything,
or if I've done something stupid...
* click on my MichaelAtOz label, there is a link to email me.

Unless specifically shown otherwise above, my contribution is in the Public Domain; to the extent possible under law, I have waived all copyright and related or neighbouring rights to this work.
Obviously inclusion of works of previous authors is not included in the above.


The TPP is no simple “trade agreement.” Fight it! http://www.ourfairdeal.org/ time is running out!