A little technique that I tried today turned out well. Perhaps it will be of use to others.
I had a neighbor/friend who was a highly skilled woodworker, with far more experience than I. Some years ago he gave us two trivets that he had made. They were composed of a ceramic tile on a hardboard base, framed with four thin pieces of wood joined at 45 degree mitered corners. The problem was that the wood framing pieces were a fraction HIGHER than the tile. Whenever my wife put a hot pot on them, she noticed burning and blistering of the wood and its lacquered finish. She got in the habit of putting several layers of aluminum foil on top of the trivets whenever she used them. To me, this was a messy solution.
Several ideas came to my mind, but I was aprehensive about offending my friend if I should attempt to revamp his nice gifts. Not long ago, he moved to another state, and my inhibitions began to vanish, knowing that I could try something without his seeing my handiwork, skills, or lack of same.
Today, I put a 1/2" Diameter end cutting bit in my router, mounted in the router table. After carefully adjusting the fence to expose the bit at only the width of the wooden frame (making certain that it wouldn't contact the tile) I raised the bit about 1/32" above the table, placed a stop at a position to terminate the cut about 1/4" before the end (to prevent splintering) and proceeded to cut down all four sides flawlessly. They now are below the level of the tile, and after I locate a little finish to daub on the exposed wood, we will have dispensed with the "unworkman-like" aluminum foil! :-)
Godzilla