i've been struggling with the best/easiest way to physically model a hollow sphere...
essentially, my project is a hollow sphere submerged about 75% into the ground topography with the exposed quarter laterally displaced one direction and the lower quarter shifted equally in the opposite direction. The remaining middle section is cut open to expose the hollow center.
diameter of the sphere will likely be in the 4-8" range.
styrofoam was a mess during my initial concept models, so i'm considering plaster of paris, but i'm not sure how i would form it out.
any suggestions or other material recommendations?
How thin do the walls need to be? I seem to remember waaaaaay back in my thesis year that a classmate was doing a similar project.
He ended up laminating a bunch of wood together, the spending lots of time on the lathe in the woodshop. Similar technique to making a wood bowl. He had nice results.
the cheap plastic balls probably wont retain their shape if you cut them but you could use them as a base and wrap them in those dry plaster strips that you can buy at art stores (like what preg women use to cast their bellies)..those are relatively cheap, easy to work with and make a nice smooth lightweight shell formwork, but of course you'd have to do it in 2 halves.
after you have the 2 formworks, you can pretty easily make the two sphere halves out of plaster, resin/fiberglass, etc. and glue them together...with most materials you should be able to sand the seam away (assuming you're not going for transparent)
you can do a whole lot with balloons. I might thing about painting latex or trying to fiberglass a baloon form. maybe some combination of these things to make formwork that will hold up for plaster or something.
you can also make it in slices in blue foam and then sand it smooth. NOX does this sometimes for blobby models.
what you can do with pre-made spheres, if they don't match the dimension you want is use them as a core to build up to a better dimension using some of the above methods.
whatever method i use, i'm pretty sure i'll have to form it in halves.
i also need to use a method that's somewhat easy to cut since i'll need to separate the latitudinal top and bottom pieces and cut away the scoop-out opening on the middle section. thickness only needs to be 1/16" or 1/8" so this should be relatively simple.
<btw, sorry if my descriptions are hard to visualize>
it seems like the least complicated technique is plaster strips or papier mache wrapped around a ball or balloon. oh, and chocolate.
the plaster strips will only give you the negative formwork based on the original ball form though. You'll need to use something you can pour or apply to the inside of this formwork to make the final model with a smooth outer finish...in the end it will essentially be a complete duplicate of the original ball out of whatever material you choose, only in two halves.
Resin from any art store mixed mixed with hardener and ordinary fiberglass insulation can be applied like cake frosting to the inside of the formwork and gives a very clean strong thin and lightweight shell that can be easily cut with a gentle jigsaw/ryobi tool, and sanded, and painted. The problem is resin is incredibaly messy, smells awful (you'll need a paint booth), and could take upwards of a week or two to completely dry to the touch...but the final product is great.
You can also use plaster to do the same thing...i'd suggest you use a combination of a thin layer of plaster of paris right out of the box mixed with minimal water so that its not too drippy, again spread like cake icing to the inside of the formwork as a first layer, and then use more of the plaster strips as a second layer for reinforcing (plaster is brittle).. it should dry as a complete shell to which the outer orignal formwork can be peeled off. the final product should also be pretty easily cut with a saw and can be sanded smooth. if you do this i'd suggest treating the final product with a spray on resin, also available from any art store very inexpensively, which will give the plaster a smooth polished stone look and prevent it from chipping.
all of the above materials are i believe relatively cheap enough for the size of project your talking about that you can easily experiment a little first to see what feels right in terms of what you're going for.
Styrofoam spheres ala 3rd grade solar system project...wrap in plaster, leave a hole to pour acetone or gasoline into, styrofoam melts away, BAM, hollow spheres
sweet! and the learning continues. i'm assuming the acetone/styro run-off sludge is fairly toxic? i don't plan to drink it, but i imagine i should do it in a well-ventilated area.
physically modeling a hollow sphere
i've been struggling with the best/easiest way to physically model a hollow sphere...
essentially, my project is a hollow sphere submerged about 75% into the ground topography with the exposed quarter laterally displaced one direction and the lower quarter shifted equally in the opposite direction. The remaining middle section is cut open to expose the hollow center.
diameter of the sphere will likely be in the 4-8" range.
styrofoam was a mess during my initial concept models, so i'm considering plaster of paris, but i'm not sure how i would form it out.
any suggestions or other material recommendations?
thanks in advance!
balloon
.stl
with the plaster i mean...
oop, dammson got there first. A balloon could also work with paper mache.
hmm...i've also considered going to target and getting a couple of cheap plastic balls out of the big cage and cutting them in half for the forms.
theres always christmas tree ornament...
what Zoë Coombes suggested...you can buy steel hemispheres at a steel shop also...
How thin do the walls need to be? I seem to remember waaaaaay back in my thesis year that a classmate was doing a similar project.
He ended up laminating a bunch of wood together, the spending lots of time on the lathe in the woodshop. Similar technique to making a wood bowl. He had nice results.
the cheap plastic balls probably wont retain their shape if you cut them but you could use them as a base and wrap them in those dry plaster strips that you can buy at art stores (like what preg women use to cast their bellies)..those are relatively cheap, easy to work with and make a nice smooth lightweight shell formwork, but of course you'd have to do it in 2 halves.
after you have the 2 formworks, you can pretty easily make the two sphere halves out of plaster, resin/fiberglass, etc. and glue them together...with most materials you should be able to sand the seam away (assuming you're not going for transparent)
go to jmichaels and look around you'll find something that will work
thanks for all the great suggestions everyone.
yeah vado, i've scoured the aisles at michaels a few times already but was having trouble matching materials with techniques.
got some ideas brewing now though...thanks again all!
.
actually 2:37, i was hoping you'd weigh in on this.
you can email me and i'll go over it with you
i think you should make it out of chocolate...that'll be sweet!
metal cooking bowls???
you can do a whole lot with balloons. I might thing about painting latex or trying to fiberglass a baloon form. maybe some combination of these things to make formwork that will hold up for plaster or something.
you can also make it in slices in blue foam and then sand it smooth. NOX does this sometimes for blobby models.
what you can do with pre-made spheres, if they don't match the dimension you want is use them as a core to build up to a better dimension using some of the above methods.
...then you can give it to your girlfriend for her to eat...
to get it precise, you'd have to lathe it in two halves, wouldn't you?
whatever method i use, i'm pretty sure i'll have to form it in halves.
i also need to use a method that's somewhat easy to cut since i'll need to separate the latitudinal top and bottom pieces and cut away the scoop-out opening on the middle section. thickness only needs to be 1/16" or 1/8" so this should be relatively simple.
<btw, sorry if my descriptions are hard to visualize>
it seems like the least complicated technique is plaster strips or papier mache wrapped around a ball or balloon. oh, and chocolate.
the plaster strips will only give you the negative formwork based on the original ball form though. You'll need to use something you can pour or apply to the inside of this formwork to make the final model with a smooth outer finish...in the end it will essentially be a complete duplicate of the original ball out of whatever material you choose, only in two halves.
Resin from any art store mixed mixed with hardener and ordinary fiberglass insulation can be applied like cake frosting to the inside of the formwork and gives a very clean strong thin and lightweight shell that can be easily cut with a gentle jigsaw/ryobi tool, and sanded, and painted. The problem is resin is incredibaly messy, smells awful (you'll need a paint booth), and could take upwards of a week or two to completely dry to the touch...but the final product is great.
You can also use plaster to do the same thing...i'd suggest you use a combination of a thin layer of plaster of paris right out of the box mixed with minimal water so that its not too drippy, again spread like cake icing to the inside of the formwork as a first layer, and then use more of the plaster strips as a second layer for reinforcing (plaster is brittle).. it should dry as a complete shell to which the outer orignal formwork can be peeled off. the final product should also be pretty easily cut with a saw and can be sanded smooth. if you do this i'd suggest treating the final product with a spray on resin, also available from any art store very inexpensively, which will give the plaster a smooth polished stone look and prevent it from chipping.
all of the above materials are i believe relatively cheap enough for the size of project your talking about that you can easily experiment a little first to see what feels right in terms of what you're going for.
Styrofoam spheres ala 3rd grade solar system project...wrap in plaster, leave a hole to pour acetone or gasoline into, styrofoam melts away, BAM, hollow spheres
sweet! and the learning continues. i'm assuming the acetone/styro run-off sludge is fairly toxic? i don't plan to drink it, but i imagine i should do it in a well-ventilated area.
good stuff.
How did Boullee's interns do it?
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