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I was disappointed by the performance of the stock J1 fan and duct design. I designed this version that keeps roughly the same profile and size as the original back cover. I spruced up the venting a little to allow better cooling for the stepper motor and the hotend heat sink. It is a bit difficult to print and I did use dissolvable supports since I was printing in ABS. If you have a well-tuned PLA profile then the small geometry shouldn't be as big of an issue. The ducts were able to be printed without supports.
Required Hardware:
2x M3x4mm button head screw (I think anywhere between 3-5mm will work for the length)\
2x M3 threaded insert
2x 5015 fans (The front cover will need to be removed and the mounting holes need to be trimmed as the picture indicates)
2x Fan connectors (I'm not sure what connectors are used on the J1, the original connectors can be cut and resoldered to the 5015 fan)
Installation:
The author marked this model as their own original creation.