Issue with Joining Surfaces, Shaded View Problem

Hey! Does anyone know why these surfaces change so drastically after I join them? I created these surfaces in parts with two rail sweeps. Please see the attached screen shot:

before joining

after joining

Hi Bo,

That looks like a render mesh issue. It appears that the surface on the bottom may have kinks in it from the input curves and that could be involved. If you still have this file, please post it and I’ll take a look. In general, the default render mesh settings should work fine for a form like this so I suspect a geometry issue. You can also change the render mesh settings for the file in File>Settings>Mesh.