Hello,
I am very interested in the RepRap project and I'm very excited for when the design for the Mendel gets released.
Now, I'm really sorry if this is redundant or in the wrong section, but I thought of an idea for solving a potential problem when dealing with a metal extruder. From what I understand, it is difficult to build from metal because it might not stick as easily. The solution I came up with is to surround the section of metal with a filler substance (like a mould) and then to fill in the metal later. Then the filler substance can be dissolved away.
Thanks for listening and I hope this helps. : )