Some time back I stumbled across the reprap project (www.reprap.org) a worldwide open source project initiated by Dr Adrian Bowyer at the university of bath the goal of which was to design and build an affordable 3d printer that could self replicate ie print all it's own parts.
Now 3d printers are nothing new they've been around for quite a long time and will print in a variety of materials the most advanced ones are now able to do full colour prints or even print in metal. The down side is these things are huge and very expensive a basic model is typically in the tens of thousands of pounds and the size of a fridge freezer and you typically have to pay over the odds for the feed stock (the old ink cartridge trick where they get you not only for the printer but the ink it uses).
So along comes reprap a project to design and build something a little more affordable for use in the home and as things stand you can get a machine for under a thousand pounds depending on how much effort of your own you want to put in.
Reprap is a Fused Deposition Machine and uses thermoplastic as it's primary material (though there are plans for other materials in future) it takes in the plastic as a filament pushes it into a heated nozzle that melts it and extrudes it out of a small hole as a thin (usually 0.5mm or smaller) stream of plastic basically like a souped up hot glue gun (some of the initial prototypes were made from a hot glue gun). This extruder head is attached to a cartesian robot that can move it in three dimensions laying down the object one 2d slice at a time one on top of the other the plastic fusing to become a 3d object.
When I first started looking at reprap they had a series of prototypes but they were not at a version 1.0 yet plenty of people had tried various things but it was all a bit up in the air. As time went on they developed the first machine code named "Darwin" which was a sort of box shape made of rods with a bed in the middle that could go up and down on threaded rods and a print head mounted on the top able to move about on a belt driven X and Y stage. you can see an example here http://dev.www.reprap.org/bin/view/Main/RepRapOneDarwin.
It was still a lot of work to make one at this stage the electronics could be got in kit form but you still needed to machine the nozzle and somehow get hold of a set of printed parts to make up the frame. Eventually various outfits started producing kits a group called Makerbot in the US came out with their own design called Cupcake CNC and in the UK BitsfromBytes came out with the RepMan these machines were not technically repraps even though they derive from that same technology but what is called a repstrap a machine that is put together using traditional manufacturing techniques but that could be used to build a reprap so bootstrap the process.
I saved up some cash and got myself a Repman version 3 complete kit which included everything needed to put the machine together. The design is a fairly close variant of darwin the parts for the corners and so on are not printed in this case but made from laser cut acrylic and assembled by a series of nuts and bolts. I got the kit sometime last year but due to being away a lot and making a series of screwups I only now got the thing together.
It's driven by a pic microcontroller which runs the four stepper motors (X, Y, Z, and extruder) it will take an file written in GCode (a semi standard that is used on CNC machines) off an SD card to print out an object in a variety of thermoplastics. I'm currently using ABS which is what lego is made out of. You can basically take almost any model export it as an STL file run it through a program called Skeinforge and it will convert it to GCode that can be printed. It also has a nice little OLED screen that tells you what it's up to (the interface to which is very fragile basically a load of strips of tinfoil and caused me to have to replace it once before)
The extruder uses a screwthread driven by a stepper to pull in 3mm plastic filament into a metal nozzle which has been wrapped in nichrome wire. The wire, which is used in hair dryers and toasters and so on, heats up when a current is passed through it. A small thermistor on the tip allows the board to regulate the temperature and when it reaches 230 degrees or so (depending on what plastic you are using) it drives the filament into the nozzle extruding thin string of plastic.
Because of the way the device works laying down layer after layer it has a limitation of not having anything more than 45 degree overhangs because it can't deposit plastic into thin air there needs to be something holding it up. One way round this is to use a support material either the same plastic making thing supporting columns you cut away or some other material that is easy to remove (this is a future improvement to the machine). Usually some clever design can do without the need for support material.
So far I've been mainly calibrating and fiddling with the software to get a good quality of print out I've made a few objects with varying degrees of success a small mug, a little toy car, a dodecahedron. The software that generates the GCode is fairly complex and getting the settings right to get a good quality of print is tricky but I'm getting there.
One of the interesting things about the reprap project is that each machine can print parts for other machines even the next generation it can also make spares for itself or incremental upgrades and new parts for it. So people have already designed most of the spare parts for my machine as well as a couple of different print heads like one that takes a dremel tool to do lightweight milling. There are also sites dedicated to making things on the printers like http://www.thingiverse.com/ who offer designs other people have made. It's a very community orientated project with a lot of contribution from general tinkerers. One of the current problems is plastic warping on larger builds, this is due to the fact that as plastic cools it shrinks slightly and this tends to mean the lower layers of a print curl upwards. Various people have come up with various modifications to alleviate or fix this like a heated print bed that keeps the plastic warm enough that it doesn't warp or new ways of designing your objects to distribute the stress as it sets.
While I've been building my "Darwin" variant the reprap people have developed a version 2 of there printer code named "Mendel" (http://objects.reprap.org/wiki/RepRap_Version_II_Mendel) and should I want to I could use my printer to print out the parts to make one of these I would just need to add some electronics and a few rods and screws to it. Or I could take parts of it I like adapt them to my existing printer. It's wonderfully flexible in this manner since it is all open source people take the designs improve and modify as they see fit and ideas and improvements feedback into the design of the next generation machine.
As to what I'm going to do with this thing now I've got it the possibilities are endless I can make almost anything I could want out of plastic using it and plastic is fairly cheap. I have a few ideas for projects I'd like to try but at the moment I'm just learning how to configure the thing and get the best out of it. I'll probably print off some spares first of all since it's structure is made of laser cut acrylic which is not the most robust of materials there are already a couple of bodged repairs on some of the stressed parts. There are also some potential improvements I could make most of the extruders have moved to pinchwheel driven systems rather than the screwthread mine uses so perhaps I could replace that.
You can see photos and a couple of timelapse videos of the machine and stuff I've thus far made with it on my picasa album http://picasaweb.google.com/warriner.matt/Repman#