Curving tubes is described at: bikecad.ca/curved_tubes. Be aware, that you can also display the angle of the bend on your drawing. While you cannot directly enter a value for this angle, it is fairly straight forward to get the angle you need by tweaking other dimensions and observing the effect that that those changes have on the angle. There's a discussion of this in the context of seat tube bends at: bikecad.ca/seat_tube_bend_angle. Also check out the video at: bikecad.ca/problem_curves. You may also find it useful to add in some user dimensions (bikecad.ca/user_dimensions) to be sure that your design is matching up. Also, you can bring in a photo of your stays and manipulate the drawing until they match. This is described at: bikecad.ca/import_photo.