Project Shellter - Shell 01

by TeamTeamUSA, published

Project Shellter - Shell 01 by TeamTeamUSA Oct 23, 2011

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Project Shellter - Shell 01 by TeamTeamUSA is licensed under the Public Domain license.

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UPDATE 2011-10-25
I uploaded shell-012948.stl, the file as exported from Sage, for shell thickening experimentation. It was mirrored from the original exported file because a hermit crab needs a right-handed shell spiral due to the way its abdomen curves.

Pimp out your hermit crab!

This is the prototype shell for Project Shellter, the current artist residency at MakerBot Industries.

It is modeled on the shell of the Cittarium pica sea snail, http://en.wikipedia.org/wiki/Cittarium_pica, and is similar to the ones that crabs in pet stores typically sport.

It was created using Sage, http://sagemath.org, exported to an STL using a modified version of Christopher Olah's plugin, http://trac.sagemath.org/sage_trac/ticket/7744, and thickened in 3DS Max.

You can explore other shell shapes here http://sagenb.org/home/pub/2928 (account required).

The goal is a workflow using open source tools, but the conversion of the surface to a solid at this point requires a commercial tool.

Maybe someone can figure out a way to thicken the surface without 3DS Max‽

Follow Project Shellter progress here:



This was printed on a Thing-O-Matic with Mk 7 extruder at the world famous BotFarm using Matt's excellent support settings: http://www.makerbot.com/blog/2011/06/27/makerbot-microtip-using-the-support-features-in-skeinforges-raft-tool/

Some notes:

  • It is oriented to eliminate interior support settings; re-orient at your own risk ;)
  • You only need the STL or the zip file; they contain the same thing
  • Once printed, the minimal support material is easily removed and the entire shell is hollow
  • Sanding or tumbling to smooth the surfaces is optional but recommended (more on this later...)

You can print it, I know you can!


Thanks to @JonMonaghan for the 3DS Max-fu, print and photos (my first print failed, and he kindly reprinted it for me so I didn't miss my flight).

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Is PLA plastic safe for hermit crabs?

Comments deleted.

Thanks! Printed the Shell-01-100.stl with pretty standard settings on Slic3r  0.9.1, but had issues with the shell-012948 which from what I understand should be the functional shell, correct?

Unfortunately, there is an error in shell-012948 that I don't know how to fix. Netfabb renders the entire outer shell as red color when it should be green (note the inside of the mesh is green). The automatic repair algorithms are not resolving the issue....

I have an idea for combining 2 processes to create thicker shells..If you use an electro-conductive paint on the outer surface of your 3D printout (various metallic paints), you could then put your maker-bot printouts into seawater and electrify them to grow a limestone surface. I am currently experimenting with this mineral accretion process to grow corals in closed systems, and also developing some small steel spirals and squares for "bit-o-biorock" pendants--one of last year's kickstarter rewards for "Living Sea Sculpture: contemporary art as coral refuge." http://www.kickstarter.com/projects/958753974/living-sea-sculpture-contemporary-art-as-coral-refhttp://www.kickstarter.com/pro...

I will keep working on my steel spiral "pendants" and see if they might become good Project Shellter potential: creating the shells with only minimal metal armature and a predominance of limestone accreting by low volt DC electrolysis running through seawater...Or, taking my snails that i eat fro
m the garden and rather than making candles from their empty shells, i could run some thin steel mesh/wire over them and try to build up a "fortified" calcium carb shell..have to try it!

There are hermit crabs at the Sea Horse Aquarium and Supply where I'm experimenting, so we can see...A friend ju
st shared this link and it seems there are so many connections in my life to snails/shells, 3D printing (Coraline), corals and Calcium. I have cast cement snail shells before, but of course, they were solid and lifeless. i love this exploration. I will follow it:)

Congrats on the funding your project! :)

Love your idea of creating a mineral surfaced shell through electrolysis. Do you think a metal-leafed plastic shell would work too‽

This is the Sage equation I used:

f = (k^u(1+cos(v))cos(u), k^u(1+cos(v))sin(u), k^usin(v)-ok_2^u)
obj = parametric_plot3d(f, (u,0,7pi), (v,0,2pi), plot_points=[res,res], frame=False, aspect_ratio=[1,1,1])

You can see it in action here: http://sagenb.org/home/TeamTeamUSA/3/http://sagenb.org/home/TeamTea...

Even after creating an account http://sagenb.orgsagenb.org tells me "You do not have permission to access this worksheet"

What equation did you use?

Very cool!

I'm really glad you were able to make use of my sage code. You may like surfcad, which was based on that and may be more suitable for your purposes. You could probably make a thick version with it.


You may als
o be interested in my latest CAD project, ImplicitCAD:


Blender 2.5 has a "Solidify" mesh modifier that should be able to do the surface to solid conversion you're after.

I'd be glad to try it and report if it works well for this model, if you'll post your surface-only intermediate STL.

Surface STL uploaded. Please post your results. Would love to have a completely open source workflow! :)

There seems to be some misunderstandings about the project. Here are some clarifications:

  • The final shell material has yet to be determined; plastic is being used for prototypes
  • No printed shells have been distributed in the wild
  • The goal is to create a printable hermit crab shell for domestic use thus reducing harvesting of natural shells


Why do you think it is ok to dump plastic in the ocean? Your heart is in the right place but this is a horrible idea and implore you not to further pollute our oceans with these things.

This is for hermit crabs that are kept as pets, not "dumping in the ocean." Reducing the demand for natural shells in the pet industry will make it that much easier for wild crabs to find natural shells to live in.