You all know I used WIDE purfling all the time. Here is a tutorial on how I did it. My purfling was usually around 5/16" wide and usually overlapped the INSIDE of the kerfing. Here's how I did it.
I made a jig from an old Stew-Mac violin purfling cutter like this...
I also used carbide "burr bits" that were very sharp.
Set the depth for 1/2 the depth of the top at the edge and routed the inside cut. Doesn't much matter which way you rout as it's a burr, but I used to follow my pencil lines and arrows to get the proper cut direction.
Note the little plexiglass "mount" that sits on the top. It's screwed to the jig with a few 2-56 bolts.
I used to freehand rout the outside scrap off to end up with a nice ledge.
The real secret of the whole setup is taking the time to carefully file that inside ledge smooth. A 1/8" piece of spruce cut to the waist shape with 120 grit glued to it takes care of the waist.
Ledge was removed by very sharp chisel or just routed off freehand.
Binding ledge was cut with a Stew-Mac setup and also cleaned up with a file just to be sure.
Purfling was always installed, then it was filed a tiny bit if needed.
Finally, the binding was installed separately.