Hi Danny, thanks for giving that one a try!

It's an interesting result - it looks like it is forcing the miter join by warping the ends of the sweep, I guess maybe in the same kind of tweaking of the control points at the end, although maybe it is a bit different than the other one.

That produces a kind of miter-join result but at the expense of not having fully regular thickness tube, just by eyeballing it you can see the thickness is different in these areas for example:





Here you can see why there is not a constant thickness - here I've set up a bunch of isoparm curves on one of the other surfaces and as you can see the warping at the end causes a kind of slanting to the cross-sections in the generated surface, they are not perpendicular to the central rail anymore:




However, that does not seem to really be a particularly bad result, because I'm pretty sure that it is a physical impossibility to maintain constant thickness in this situation and also have a nice matching miter, you can have either one or the other. And if you have bothered to have a single joined rail curve with a kink in it, I guess that probably means you are actually more interested in the miter.


- Michael