40 mm air duct for Robo3d

When I got in charge of the Robo3d Printer I printed this for, we were having a clogging problem. After reading [this guide](http://support.3dverkstan.se/article/23-a-visual-ultimaker-troubleshooting-guide#grinding) we decided that the printer extruder needed more ventilation.
In order to be able to attach a bigger fan, I designed this piece from the shape and dimensions of the printer cart.
The piece is sideways to increase the conctact area with the bed.
It has a significant drawback: be