Peter, that is in my opinion the single best way to make a dado cut! By the way, dadoes go across grain and grooves go along grain. When it is plwood I have no idea of the proper name! This jig can make dado and groove cuts. I've been using one like this for many years (mine is much simpler) and it never fails me - I just have to remember to always load my router with a 1/2" diameter bit (which is always smaller than the width I am routing). Your jig pictured here looks very nicely made! Keep-up the good work!
OPG3 Tweak everything!