After many attempts, endless tests and improvements, heat sink and  other stuff,finally we've got a Bowden type extruder working and not oozing.
It was the aim of a little research we  made in our workshop. 
The tests shown below present various printed parts that were needed to modify the parameters of the system.
Of course we could not expect a perfect result at first print, but it was really not bad.

Aluminum X-carriage V2 Available for shipping
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Aluminum X-carriage V2

Comparing two techniques for rapid prototyping.
A four axis CNC milling machine and a 3D printer