Pyritohedron, Creating Solid from edges

Replies to This Discussion

Permalink Reply by mark zirinsky on November 23, 2014 at 2:02pm

Andrei/Sarah,

interesting.

in the mineral world, we see 'skeletal crystals', where just the edge of the crystal grows but not the centers of each face. this can also be called a 'hopper' crystal. gold, galena, flourite, show this. So, how can we tweak this def so that each of the 5 meshes of each face, tilt inward at, say, 15 or 30 degrees, and then have a flat face at the end of this? should the mesh be rotated around the line of surface intersection, or would it be easier to move two of the 4 vertices offset along a normal vector?

Permalink Reply by Andrei on November 23, 2014 at 3:59pm

Mark,

one of our colleagues, Jonathan is looking into Bismuth crystals:

http://wewanttolearn.wordpress.com/2014/11/11/bismuth-crystal-growth/

Have a look at his work!

Best

JAM.d

Permalink Reply by mark zirinsky on November 23, 2014 at 4:25pm

hi Andrei,

nice work with the Bismuth. Some years ago I looked at how to model galena (PbS) skeletal growth when in the presence of Silver (Ag), so your crystal lattice becomes PbS and AgS; and was able to get some theoretical correlation between the difference in atomic weights and distortions in the crystal lattice, as observed in naturally formed galena specimens.

Back to the pyritohedron. An issue I have with meshes is that, in my case, the end product is usually CNC'd, so I need a solid to work with. Taking the script one step further, extracting end points of the mesh, moving along a vector, and then creating a surface, now we can tweak the shape to me more interesting. 

Still puzzling over how to make a plane out of the centermost pentagon.

Permalink Reply by mark zirinsky on November 23, 2014 at 5:30pm

oh. feed the vertices into 'patch' surface.

and, voila.

Attachments:

• pyrithoderonfb-skeleatl-2.gh, 16 KB

Permalink Reply by Andrei on November 23, 2014 at 7:13pm

Mark,

Thank you for the update,.

I always use meshes because of the great speed advantage.  I do not know much about CNC - how does it constrain you to using breps?

JAM.d

Permalink Reply by martyn hogg on November 23, 2014 at 11:59am

Works well with exoskeleton but perhaps not what you are after.

Attachments:

• 20141109PyritohedronEXO.gh, 32 KB

Permalink Reply by Sarah Stell on November 24, 2014 at 7:44am

Hey Guys,

Thanks so much, I've sorted it using Andrei's scaling technique. Thanks Martyn - the exoskeleton does look really good but I'm hoping to fabricate it using flat materials so needed to create surfaces. The patch also worked Mark

Thanks again for all your help

Sarah

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