For my MK1 I had replaced the normal cooling fan with a ballbearing radialfan blowing fresh air from the side. I had very good results with it. It looked a bit ugly and with printing the contruction would always bend a little because of the heat, but it worked. After my MK2 upgrade I installed the fan that comes with it. Also a radial fan but not that good.
That thing would only give a light breeze. Not enough for proper cooling of PLA with small detail or overhanging structures. Because of the BL-Touch sensor i could not use my old radialfan setup anymore, the sensor was there now.
So i decided to design a new cooler, for both MK1 and MK2 owners. One that works and looks much better.
It uses the old MK1 "hotend blower" as it's better heat risistant than home printed ones. You need to use those original 3 screws to mount everything at the bottom. Just like the original fan.
On top of that it cools in 2 directions, also cooling the downside of the hotend firewall, after that the air is pushed out towards the hotend. Gets the temperature down by wuite a margin. From alsmot to hot to touch to body temperature (dont have a thermometer).
The weight of the cooler is more towards the X bar now.
I reached version 4 by now, it fits great and it works really well. You need to remove the small cable clamp at the right side, but there is a notch to keep the cables in place included in the design.
Did i mention it's the best looking cooler for the D9?