Thank you cino.cihan and Dave R. for responding.
I already used two different materials to show the joinery in a clearer manner, but, thickening the edges, is also helping to make the joinery perceptibly clearer yet.
Dave R., I understand your point, too. A rendering program will default to showing the edges no matter what was done in SU.
I am learning a lot from all the experienced users on this forum. Thanks to everyone who has responded.