For those of you asking for an Ender 3 "PRO" Bullseye duct to fit the wider attaching points for the 4010 fan on the PRO, here you go. It should accommodate the extra width nicely. This also fits the CR10 Mini and the 2020 version of the Ender 3.
The file is:
Ender3ProBullseyeDuct10.19
Dave
...................................
2/25/20
A user messaged me that this will also fit the Cr10 Mini which uses the same fan as the Ender 3 Pro.
Print with 4+ walls with 50%+ infill. These are structural parts and need to be strong, especially the mounting points.  

9.27.2018  I adjusted the duct to have a little thicker arms around the holes and changed the larger inlet so you won't need a calibrated printer.  
................................................................................................  
I’ve had some questions about the duct height and the Petsfang v2 and Bullseye. I decided to borrow a colleagues' smoke generator to give a better visual of the airflow since the "water tests" only show the turbulence.…

Let's keep it cool!
My take on a better cooler for the CR-10 Tronxy X1/3 type hotend. The stock CR-10 set up can cool the heater block too much if you don't have it wrapped. The parts doesn't cool all sides well. My Tronxy X3 didn't have a parts cooler and the heater block couldn't get temps over 205C.
I tried a couple other popular coolers but did not fit my original parts blower or just not that efficient.
So the Mittens Cooler evolved. Printed in PETG, it weighs 12 grams. Has a bit fo a twist for a little vortex of air.
Needs a few things: a 5015 blower/fan, a few screws, a bit of rewiring, and a bit of tenacity.
Reportedly works with the Tevo Tornado now.
WARNING: It works for me. Your results may vary wildly.
I've gone through dozens and dozens of printed revisions to get to this version.
If you find this useful and want to encourage my insanity, buy a cup of coffee for me, a bag of coffee, or you pick the value. Thanks!
Please note, this is not compatible with the auto-leveling sensor. Send me one and…