I have two Hemera tools on my TC, design is based on Greg's but using two Duet 3 Tool Boards as described at https://miscsolutions.wordpress.com...l-changer-to-duet-3-with-hemera-tools-part-1/ and subsequent entries on that blog. The print cooling fans are 12V versions of the Winsinn centrifugal fans used in the original Bowden tools. I noticed that the print cooling fan on one of my Hemera tools didn't always start, so I removed the fan duct assembly to investigate it. What I found was that the Winsinn fan doesn't work when its back is mounted right against the Hemera stepper motor. It needs at least a 1mm gap to run well. A 2mm gap is sufficient for it to run at full speed. This issue isn't unique to the Hemera stepper motor, the fan also stops if I hold the back if a different stepper motor against the back of the fan. So I need to modify the fan duct to hold the fan slightly away from the motor.