If you read my interests, you probably know that I love studying the 3D printer we have at school to see how it works. If anyone wants to know more about 3d printing, there is a really cool article here. Anyway, I spent about a month (as an engineering student I know how important research is) sketching designs and building prototypes. After that I finally found a design that fit my needs. This printer is based on the brain of a mindstorm NXT because it is easy to program and my arduino chip is burnt out and I'm still trying to save up to buy a new one. This printer only prints as accurately as you program it, but I will show you the best method of programming. The design includes x-axis and y-axis movement as well as z-axis movement used to pump down the printing material.
Time to make: about 4 hours if you have all of the pieces in front of you
Parts: Lego mindstorms kit and assorted lego box as well as a hot glue gun, tin foil, string, a printer, ink for the printer, a computer, and power to you house.
What did you make: I used the above parts and about a months worth of research to develop my design for a 3d printer that prints out a glowing material as accurately as you can program it. Not nearly as good as an industrial one, but a great project nonetheless.
How did you make it: I worked alone and used the 3D printer in my school as reference to how to build one. I had about 50 different design sketches before I started to prototype and then I had 3 prototypes.
Where did you make it: I created this in part at school (sketches) but mostly at home. I spent whatever extra time I had free from homework to work on this project.
What did you learn: I learned the importance of good and thorough research as well as refining my skills as an engineer.

Step 1: Before You Start...

The type of 3d printing shown in this instructable is called extrusion printing. This is when a hot material is programmed to be applied layer by layer to a surface in order to create a 3d object. In this process, we use hot glue as the material. This process can use multiple colors too! If you have a look at this link you can see how to make your own or you can buy color hot glue sticks.
Motor Uses: two motors for x-axis and y-axis movement, one motor for applying the hot glue.
How it works: The two motors move a base plate any direction and then hot glue is streamed down using the third motor.
Glue gun preparation: For this to work, you will need to open up your hot glue gun and remove the trigger. MAKE SURE IT IS UNPLUGGED FIRST. This will allow the hot glue to be freely pressed down. Be careful not to disturb any wiring inside and remember, these companies like to hide disassembly screws underneath stickers.

Step 2: Assembly X-axis Movement Part 1

Part 1 covers basic x-axis movement.
There are some parts that are not included in this step that you can either find or you can find alternatives

Step 3: Assembly X-axis Movement Part 2

A continuation of basic x-axis movement

Step 4: Assembly X-axis Movement Part 3

Preparation for y-axis movement

Step 5: Assembly Y-axis Movement Part 1

This part will go over the basic gear structures and how they interact to accomplish y-axis movement.

Step 6: Assembly Y-axis Movement Part 2

This shows you how to build the basic platform and the plates that hold it in place

Step 7: Assembly Z-axis Structure Part 1

The start of a very tall 3d printer...

Step 8: Assembly Z-axis Structure Part 2

Connecting the structure to the x-axis movement

Step 9: Assembly Z-axis Structure Part 3

Building the resting platform for the z-axis glue applying mechanics

Step 10: Assembly Z-axis Structure Part 4

Making the glue-gun holding platform and adding to the height of the printer

Step 11: Assembly Z-axis Structure Part 5

This adds much needed support and weight to the back of the printer. It also includes two touch sensors that you can implement in your programming if you wish

Step 12: Assembly Z-axis Structure Part 6

Preparing the glue gun connections

Step 13: Assembly Z-axis Structure Part 7

This is a very important gear train that slows down motor speed and increases power output. This makes for a very precise z-axis linear motor

Step 14: Assembly Z-axis Structure Part 8

This is a platform to keep the z-axis pusher in line and make sure it does not move too far one way or another

Step 15: Assembly Z-axis Structure Part 9

This shows parts necessary to attach the z-axis pusher to the rest of the printer

Step 16: Methods of Printing

Things you can print on: I would highly recommend printing on tin foil as the hot glue doesn't really stick to it, especially if you freeze it. I have found that adding oil or other non polar substances so that the glue has little risk of sticking to the foil. I DO NOT recommend printing straight onto the plastic for a few reasons: if the plastic melts, BAD things will happen; if BAD things happen, I take no responsibility. Just don't print straight onto the platform. Be safe about it.

Step 17: Programming

Since programming needs a lot of motor use that slows down the software, I would recommend the use of MYBLOCKS. If you don't know how to use them, you can see how here.

Steps of programming:
1. Print out a picture of whatever you are printing. If you are printing something with multiple layers, do this one layer at a time and make sure you keep them in order. I would suggest making a separate MYBLOCK for each layer of the print.
2. Go into the NXT and move to "View". Then choose the motor and move it. You can then program the motors in degrees. I would keep motor speed between 20 and 40 percent. If you want to program curves, you can uncheck 'wait for completion' on the first motor block and keep it on the next one. Then they will run at the same time and if you have x and y axis movement you can create a curving motion. Throughout the build, features were added that make for easier data logging.
3. Use sounds to say when it is done or when the glue gun has run out of glue. These are very helpful.

Step 18: Start Printing!

You can print a large amount of things with this printer. I started by printing a few layers (5 I think) to make a 3d 'S' for Searx. Once you get good at programming layers, you can go for something larger such as a 3d head or something. If you make something out of this printer, post a comment with a picture! After printing, go ahead and turn off the lights and pull out an ultraviolet light to make your creation glow!