Titan E3Dv6 & Volcano fan mounts

This is a remix of Zeeflyboys excellent magnetic combo fan mount + cooling duct system for the E3D; simple, elegent and effective allowing quick nozzle or hot-end changes.

I had 3 teeny issues to overcome:
1 - the original duct didn't fit into the mouth of my 50mm fan. Fixed with a resize to suit what I had; YMMV.
2 - the 8x2mm N52 magnets need the sockets resized a smidge, but even with a tight press fit they were so strong they kept pulling out of the socket in the duct. I edited the duct to have the magnet inside - a faff getting it seated but once in it stays put. The extra distance between the magnets has weakened the hold a bit and the fan wobbles very slights so I may try something else like having the magnet in the original location but adding a wrap of glassfibre tape around to hold it firm. However it's yet to move enough to bump a print so I might not bother.
3 - I switch over to another hotend with a volcano block regularly so I needed a longer duct to accommodate that. A bit of Tinkercad jiggering and voila, a longer duct...

As the bits are in proximity to the heater block I used PETG at (iirc) 100% infill. The 50mm fan duct was printed upright, the cooling-block clip for the 30mm was face down. I didn't use any supports. Might want a brim if your bed adhesion is marginal but as I use printbite at 75°C for PETG I get pretty solid hold even rattling along at 50mm/s.