The next step is to surface sand both sides until the thickness is exactly 5.0mm.
..This sanding setup has an adjustable table height. Remove about 0.005" per pass, alternating sides.
In this picture, I have laid out the dimensions and locations of the bass bar; drawn on the inside of the plate in pencil.
Since I have angled the grain of this top plate is on a diagonal, the bass bar is similarly angled with the bass bar passing directly beneath the left foot of the bridge.
I have taped a piece of rough sand paper along the bass bar location and am sanding the bottom surface by using short rubbing motions. After the bar fits well, I use # 100 paper, and finally # 150. The bar is positioned upright (90^ to the plane of the edge gluing surface).
Check your work by placing a ling strip of carbon paper and rubbing. Continue refining shape until there is continuous contact.
I use two spring clamps to hold bar in position and if this is not enough (as in this case) add clamps to just remove any air gaps.
Pre fit the bass bar so you know exactly the steps you will make once you begin the gluing operation.
Let it dry overnight in a warm location.
The bass bar is glued into place with hot hide glue. Warm both parts before hand to improve bond. Brush full strength glue on to bottom of bar and over contact surface and rub into position and apply just enough clamp pressure to hold in position without air gaps.[ A light coat of half strength glue on the plate contact area first, will prevent any plate surface distortion on final glue up.]
Clamp the top plate in the plate holding fixture to that it is perfectly flat for this next fitting and gluing operation.
..The "ff" hole inner notch (bridge centerline) is 7 11/16" down from front edge of top plate = high point of bass bar depth.