I believe I have figured out how to make the carbon inner shaft:
I will use the old tail pipe from my walkera 4#3 for the shaft. It is 2,5mm but will go inside the outer shaft. Ihe inner diameter is more than 1mm but less than 1,5mm.
At the ends I will make steel ends from an inner shaft. Some part of these steel ends need to go inside the carbon pipe and these must be glued together.
I did some research on glue and I found out that epoxy woud be the appropriate glue for putting the steel and the carbon together.
The last remaining problem is how to reduce the diameter of some part of the steel ends so they will go inside the carbon pipe?
And then to actually do this