I make a template out of 1/4" birch ply which fits the bridge outline exactly. Once the bridge is positioned using a centerline finder and Saddlematic, I mark the forward edge and the ends of the wings with lacquer-safe green tape or delicate surfaces blue tape. I position the template on the top using the tape as a guide (even with forward edge of cutout and end of wings), clamp, then set depth using .003 shim stock (AKA notebook paper). I use a 3/8" bushing with a 1/4" downcut spiral bit to clean off the lacquer leaving a 1/16" lip around the edge. After sanding the bottom of the bridge to the top radius, I use a convex radiused router base plate to cut a matching rabbet in the edge of the bridge.
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