And this is something you don’t see often in the dungeön, me testing on scrap!! I tell others to do that but rately can I be arsed to follow my own advice. I drill using a drill stand, lacking a drill press in my home workshop.
Once the depth is dialled in I go for the real piece. The drill is modified to leave a smooth bottom in each hole, I shortened the brad point and the spurs.
I roughed in the upper edges of the hole, screwed the jig back together and pressed the small part into the hole. Then I can scribe around the large part to get the outline of the instrument-to-be.
And here’s the router plane smoothing out the bottom, and making it deeper in small increments. My thought is to get the hole nice looking then thinning the soundboard with a smoothing plane from the front face.
At this moment the thickness was 2.3 mm, I went to around 1.8 in the end.