Making a perfect 3D object takes far too much skill and patience for most people. With computers it’s much nicer to be able to create a file in a 3D program and have it be made automatically. These machines do exist, they’re called 3D printers, and in the past few years they’ve gotten better and more accessible for everyone. If you want something 3D and custom they’re the way to go.
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Step 1: Sand Castles
3D printers make objects one layer at a time. There are a few different techniques, but essentially each one prints one thin layer of material on top of the previous one until the whole object is made. One company, Z Corp, makes a 3D printer that builds objects with powder and a binding agent.
Imagine you have a tray and coat the bottom with a fine layer of sand. You then took some glue and drew a circle in the middle, creating a ring of glued sand. Now take some more sand, spread it evenly on top, and draw another circle with the glue, gluing a new ring of sand to the previous one. Keep repeating this process off adding a layer of sand and gluing circles and eventually there will be a glued sand cylinder inside the tray of sand.
Now, if you reach in to the tray of sand, you can pull out a hollow cylinder of sand. By choosing the radius of the circle and the number of layers you can get the exact dimensions that you want. If you made each circle a little bit smaller you would get a cone. Get creative and you can make any shape you want.
Step 2: Other Techniques
This describes Z Corp's technique, but there are other 3D printing techniques that build the model in similar fashions. Selective Laser Sintering (SLS) lays out a layer of material, but instead of binding the material, it melts it together with a laser. Stereolithography (SLA) uses a photosensitive pool of liquid as its medium and builds its models with a beam of UV light.
A different approach is Fused Deposition Modeling (FDM) which build models up by adding material instead of binding it. With this technique, plastic or metal is extruded from a nozzle that moves around on top of the model being built. Since these models don't have the other material to hold them up, they also use support material. It looks like scaffolding and when the model is finished it can be easily removed to leave the resulting piece.
Photo by fungus amungus from How to use Google SketchUp for Ponoko 3D printing
Step 3: DIY Options
Many of these machines are still far too expensive for anyone to own, however. The exception is the MakerBot which you can currently buy for as low as $650, making this an accessible option. Assembly is required, but with everything together you can start printing up your own pieces from your own desk. As long as the piece you want fits into a 4 x 4 x 6 box you'll be good to go. The resulting pieces aren't as polished as what come out of the industrial machines, but are still great for home use.
Even though the industrial machines are way too expensive for the casual user, their services are easy to access. Two websites, Shapeways and Ponoko, provide a simple system for 3D printing. Just upload a file, choose a material, and they'll ship it to you when it's finished.
So whether you want to start out by printing a few pieces or jump on in and get a MakerBot, there are definitely some solid options for making your ideas become tangible objects without all the mess of making it by hand. That way you can worry more about the design and make things that you never thought were within reach.
RepRap - desktop 3D printer
Fab@Home - desktop 3D printer
Thingiverse - share 3D files with others