For a while now I've got a 3D-printer. An Orca V0.43 to be exact.
This is a 3D-printer from http://www.mendel-parts.com/.
I'm very satisfied with the printer, it prints well, it isn't that hard to put together and it looks good.
But it doesn't support a fan to cool your prints.
The Orca V0.43 runs on the gen6 deluxe electronics.
The gen6 electronics do have a connector wich says "fan" but this is a direct connection to the 12V input. This means that the fan connected to this connector will always be on.

In this instructable I will explain how I added a controlable fan to my gen6 deluxe electronics. this instructable will probably work for the gen6 too.
With a few modifications it would also be possible to control pretty much everything. For example a heated bed for the gen6 users (gen6 doesn't support a heated bed, gen6 deluxe does).

Step 1: The Electronics

The electronics to make this work are very simple.
To control the fan I used a pin from the I2C port. The I2C port has 4 pins available, two digital pins, a ground and 5 volts.
The two digital pins are pin 16 and 17.

To switch my fan I use pin 17, a resistor, a transistor and a couple of connectors.
You can find the schematic in the picture.

Another option is the seven switch which can can be found here http://reprap.org/wiki/SevenSwitch

Step 2: The Firmware

There are a couple of things you will have to change in the firmware of your printer to make the fan work.

First things first the firmware supplied by mendel-parts does not support PWM/speed control, the fan can only be turned on and off.
To get the PWM for the fan working you will need to download the latest firmware from https://github.com/ErikZalm/Marlin
When you update to this new firmware you will need to change the configurations to match those off the firmware from mendel-parts.

The pins from the I2C connector must be defined/redefined to tell the firmware what the pins do (control a heated bed or a fan).
Defining the pins is done in the "pins" tab of the firmware. In the "pins" tab you need to find "motherboard == 5" this part defines the pins for the gen6 electronics. In the picture you can see what you will have to change.

When you're done with the firmware you need to upload it to your gen6 board.

Step 3: Hardware

now you can print the cooling tower and mount all the components.
The cooling tower I printed can be found here http://www.thingiverse.com/thing:31089