Here's you part back. The difference is that you have to create cylindrical geometry that you can actually be tangent to. There's no real benefit I can see in joining the curves together, in fact it frequently produces inferior geometry. And why you'd never bother to sweep a circular section along a centreline once you realised that the tube or cable function is for! That done creating the plane works as expected.
I am not at work right now, so I haven't tried what I am going to tell you.
Put a datum axis un the cylinders, pick the face of the cylinder and it will going down its centerline. Then when you want to make a datum plane tangent to that cylinder you pick the datum axis first, and then the face of the cylinder second. In the dialog you should be able to enter what angle you want the datum plane.
I have a bit more radical approach to what you are doing. Instead of making the bent cylinder round, initially make it square, then extract the datum planes from the faces of the square that you need, and then round the square by using blends that are a radius .5 the size of the square side.
Thanks Hudson, I forgot about the tube, don't use those features that often. So I have to trade the ugly edges where the sketch curves meet for correct geometry then.
Join curve converts primitives (lines, arcs ..) to splines.
Splines are complex entities. You're generally better off selecting primitives when available.
