SmartAlu 80mm hotbed post-printing cooling fan support

The SmartAlu aluminium hotbed is amazing (the printed pieces stick perfectly on it, it requires no glue or adhesive tape of any sort, and as soon as it's cooled down, the pieces are really easy to remove), but it's also amazingly slow to cool down after each printing.

To resolve this issue, I installed a 80mm cooling fan (the regular 12V kind that's really easy to get), and designed a two-pieces very simple support that holds it with the best orientation, and it works wonderfully : the cooling down time is reduced by a significant amount! :)

To give you and idea of its efficiency, my tests show that, in a room at 20°C, without this device, the hot bed goes from 60° to 25° in no less than 20 minutes. With this cooling device, going from 60° to 25° takes only 5.30 minutes!

To install the fan on the support you'll need four M4x12 bolts and nuts.
You can also use bolts to install the support on the bottom aluminium plate of the printer, but two-sided adhesive tape will be just as much efficient with less trouble. ;)

The general idea is just to put it in the middle of the X-axis, and at the back of the printer (without touching the Z axis!), so that when the plate is at its lowest position just above it, the fan points directly at the middle of the plate.

Then comes the wiring part…

For that, you'll need a Ramps1.4 RRD Fan Extender, that goes on the "Servos" of the MKS-Gen board (that's between "5V out" and "Aux-1").
All wiring information is detailed here : http://www.instructables.com/id/Configuring-and-using-Reprap-Ramps14-RRD-Fan-Exten/

…and the coding part :

For that, start by checking your new fan is connected properly, by sending the following command through the terminal to your printer :
M42 P11 S255
If it starts blowing, you have a winner! :)
Turn it off with :
M42 P11 S0.

Then modify your custom ending G-code so that, at the end of the printing, the plate will get down as low as possible without (of course) hitting the fan or the filament spool.

For instance, it would be something like :
G1 Z170 ; get the plate as low as possible above the cooling fan.
(on my Smartalu, for instance, this is the optimal height)

Then add these lines at the very end of your custom end G-code :
M42 P11 S255 ; turn hot bed fan on !
M190 R25 ; wait for the hot bed to cool down to 25°C…
M42 P11 S0 ;…then turn the fan off !
M140 S0 ; and turn the hot bed completely off

This way, this cooling device will start automatically at the end of each printing, and keep doing so until the printing plate has cooled down to 25° (or any other temperature would be sufficient to allow you to remove the printed pieces easily), then turn off.