Read the instructions and post at Ultimaker at:https://ultimaker.com/en/resources/20503-ultimaker-original-dual-fans-upgrade Updated with step/rhino/3ds files of the 30x30 version so anyone can change it and make their own version. Updated with step/rhino/3ds files of the 40x40 version so anyone can change it and make their own version. The Curve for the inside of the cap it's done using 'loft' on rhino, then cap it, and bolean it to the fancap extrusion. Modifying the curves of the loft you can change the inside of the cap to improve the airflow as you see fit :) Update on 50x50 fancap. Stronger bottom-left/right parts and fixed fancap because it might hit the sides on some umo (because the sidepanels have a curve and that changes from one machine to other machine Z alignment). Update. @Amedee made a very interesting mod for this fancap, so I adapted a bit to his specs the untested design v2 and now is a v3, it cools much better than the basic design but is only for 40x40 fans (IMO the best ones) So added this two files. The 'Scalable tops' Can be scaled to the user need, if you use Cura, do 'Merge' then scale the part to your needs. If you use S3D, just group and do the same. For Amedee Mod Umofancap40x40v3.STL – 1.2 mb For Amedee Mod Umofancap40x40v3 Scalabletops.STL – 370 kb