Geo Hart 72 pencil holder

by AuntDaisy, published

Geo Hart 72 pencil holder by AuntDaisy May 19, 2012
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Two pencil holders for helping to assembling George Hart's amazing 72 Pencil sculpture ( http://www.georgehart.com/sculpture/pencils.html ). When finished, they can also be used as a stand.

There is a useful assembly example here http://sumidiot.blogspot.co.uk/2008/11/72-pencils.html
and http://www.instructables.com/id/Geometric-sculpture-from-72-pencils/

Lardcanoe has also created a nifty holder http://www.thingiverse.com/thing:16293


Buy 72 pencils (mixed bright colours are fun); measure your pencils across the flats - mine were 6mm. Scale the STL so that the longest distance across the holder (the hexagon diagonal) is 16 times the pencil across-flats distance, so 96mm for this holder (i.e. 16*6mm).
There are two designs of holder, one which is solid, the other which is thinner and can flex a little. It's probably easier to start with the #2 (the springy one); as the solid one can be tight fit to the pencils.

Print 4 holders - one to hold each of the four hexagonal prisms of pencils (18 pencils per prism). Push two of them together at an angle of ~70° (or arccos(1/3) if you have a calculator & protractor ;-) so that the hexagonal prism edges (are parallel and the pencils touch. Add the next prism so it's also ~70° from the others. Cross your fingers and push in the last prism.
Elastic bands around the assembled prisms can help keep them in place while assembling.
Discrete drops of superglue will help keep everything together, especially for the pencils along the edges of the prisms.

To help visualise how things go together, I've included a ZIP-ped STL file of the full assembly (72 pencils & 4 holders) which you could view in, say, ReplicatorG.

Note: The holder was drawn up in a CAD package, but I have tried an OpenSCAD version - just not sure if the maths is completely correct.
I'm still tweaking the size of the pencil holes and their separations - if things are too tight, try printing the holder ~5% bigger.

This prints reasonably well on a Makerbot Replicator. (Although the first holders were made of balsa wood with CNC milled holes.)

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Just noticed this one. I like it! The design you have was actually my original way (i should have uploaded it as well), but I couldn't get my ToM to print something with a print area that large, so I had to break it up into smaller parts leaving me with a slight imperfection. I was probably a tenth of a mm off which meant the pencils didn't hold as well. Yours looks nice and strong, but I guess you also had to resort to some glue. Good work!

I liked your holder (quite envious of your idea of splitting it up) and I hope it was alright putting a link to it. I did it the other way round - the rigid one first, then the flexible one (which is much more tolerant on pencil variations).

Those prisms sure are fiddly to get together; but worth it. George Hart's model is beautiful (even with a tiny bit of gluing ;) ) it's on the bookcase next to me as I type.

Any chance of posting a DXF file conversion (from the STL file) for us poor laser folks to laser cut? This would be awesome - I have the pencils ready to go...

thanks, will check back.. GMT

Hi, just uploaded a DXF version of the outline of #2 (done in CorelDraw 12).

Hope this helps.

I'd love to see your laser-cut version - will you use wood or plastic/perspex?

(You lucky thing having a laser-cutter :-)

Good luck with the the scuplture and many thanks to George Hart for the original creation.

... and the DXF for the first holder (which is inflexible, so I've made the hexagonal holes a tad bigger) and the CorelDraw! 12 file (just in case).