Here are a couple of thoughts for you.dan morrissette said:Is there a handy and adjustable jig for adding keyhole hanging slots to an prebuilt projects, like a Plate Display Shelf unit?
One: make sure the slot is deep enough in the wood to hold well and long enough so it cannot easily slip out.
Two: if the shelf is long enough try to have 16" centers or multiples of 16” so you can mount to wall studs.
Three: on smaller then 16 “ pieces I like to take a ¾” x ¾” piece of pine and tap a couple of nails thru it so the points just come out maybe a 1/16” at the spacing I want. Then I use the piece of pine to locate the holes on the work piece and on the wall so they all line up.
Four: on pieces that are going to get only one hole make sure you have the balance point or they will never hang straight.
I like to use my trim router because it light weight and handy for this sort of project. I made an L shaped plywood cutout that I clamp to the work piece. I use the one side of the L to run against and the other as a stop on the top-side (where the slot is not the hole on the work piece). Keep in mind the top of the slot is where the screw stops and the starting hole is not as critical.
If you need more information before Rick gets his tip out let me know I will make a drawing or take a picture of my set-up.