Fan duct for ReprapPro Mendel fan mount

This fan duct is designed to be mounted on a 40mm attached with ReprapPro fan mount.
A fan duct is particularly necessary when printing ABS since high bed temperature means high thermal dissipation which can exceed the heating circuit ability to maintain proper temperature. This can result in your bed temeperature decreasing too much. With this duct, air is directed only near the printhead: thermal dissipation is limited for the first layers and once the printhead is a little bit higher cold