Hi Rick,
Simple is beautiful, as usual !
However, this is true because you use your probably homemade good quality vise, which has the top surface always parallel to the bottom surface.
Sadly, all my poorly made drill press vises have a badly adjusted mobile jaw, and when you tighten them they start tilting ...
Another trick maybe could be to use a magnet, half positioned on the top of the fixed jaws, and half positioned on the piece, if magnetic... then you tighten the jaws ...

Thanks for the trick Rick !
Christophe