Hi nukkle,

> 1.i tried to join c1 and c2. joining is succesfull, but
> one problem stays. the point between c1 and c2 where
> the curves are melted wont be smoothed. why?

That's actually intentional that Join does not alter the shape of objects.

Otherwise it would not be possible for example to join 4 lines into a closed rectangle.

You can put a fillet in between 2 curve segments to smooth them out, or after you have joined segments into a combined curve, you can turn on control points and delete the control point where they touch to fuse 2 segments together into a single smooth segment, that is another way to smooth things out.


> 2. i tried to extend c1 to c3. but it doesnt work. why?

It's because the tangent extension of c1 does not intersect the c3 line, it shoots off to the side of it. Here I have drawn a line from the end of c1 with "Straight snap" enabled so I could snap to the end tangent of c1, so you can see this more clearly:



- Michael