[4DThinker]

The preview screen won't show any bit that undercuts (keyhole or dovetail) but all you need is a short 2-segment vector that runs back on itself and a profile toolpath ON the line. Describe the bit as an end mill but name it a keyhole bit.

Sometime the software wants to close vectors that end on the same point they started at. I get around that by making a very slight V instead. This will taper the keyhole slot slightly but that just make it easy to find/slip over a screw in the wall. I normally run a straight end mill which has the diameter of the narrow part of the keyhole bit to clear out the center. Less work for the keyhole bit to cut the final shape.

 

[4DThinker]

You wouldn't want to ramp from the surface to the bottom of the dept of the cut. I've done a couple where I used the fluting toolpath to start 1/4" deep, ramp another 1/32" or so, then ramp back to the starting position before retracting from the wood. That was when I needed the screw to get tighter as it slid up the keyhole slot.

4D

 

[4DThinker]

Nothing wrong with cheap hardware solutions, unless you have a cnc and a keyhole bit already.

Nice thing about keyholes is you can hang your flat backed project flush to the wall.