Fitting of Bridge Feet...
...The main idea of fitting bridge feet is to make the bottom of the two bridge feet exactly match the curve of the violin top plate all over the bottom surface of both feet.
...The back side of the bridge is exactly perpendicular to the top plate (straight up and down) with the bottom of the bridge feet exactly touching the top plate.
... When the feet are properly fit, the bridge will stand up by itself in its proper place with the violin held horizontally.
... The wood dowell is exactly perpendicular to the rear block of hardwood. The front (toward fingerboard) side is the same size but is cut with an 8 degree angle face toward the inside to hold the 8 degree angle of the bridge properly.
... The metal rod is welded to the two 1/4" studs and placed in oversize holes so that this clamp is free to rotate slightly. To use, the bridge is placed with the labeled side toward the wood dowell side and clamped firmly the bottom of bridge even with the bottom of the clamping blocks) just the bridge feet stick down below.
...This tool is used as illustrated at the left. The idea is the violin is supported in a holding fixture exactly level (top plate plane level).
...An adjustable back support is raised or lowered so that the dowell is exactly level when the bridge is in position. This support has a cut out notch which positions the dowell and allows it to slide back and forth (forward and backward).
...The dowell is fitted to the bridge back support block exactly perpendicular so when this back support is raised and lowered it can be made exactly horizontal (checked with a small bubble level), thus assuring that the bridge being fitted will have its back surface exactly perpendicular to the top of the violin top plate.
...Various grades of sandpaper (face up) are held against the curve of the top plate beginning with say # 100, and ending with a fine grade (say # 600). The sanding process is shown in this photo with the bridge being moved forward and backward perhaps over a 3/4" range in the position of the bridge final position (centered between the inner "ff" hole notches). As finer grades of paper are used, and as the bridge feet are sanded down, the adjustable back support is repositioned so that the dowell remains parallel to the holding fixture (that is, horizontal).
...This view shows how the sandpaper is held during sanding so that the proper shape is developed on the bottom of the bridge feet. As you near final shape, you can make pencil hash marks across the bottom of the bridge feet as that as you next lightly sand, you can see just how perfect the developed shape matches the top.
...A final check can be made by putting a piece of (oldfashioned) typing tracing paper, ink side up, under the bridge (in position and upright), and then while holding the bridge in position, pull the tracing paper out, which will mark the bottom of the bridge feet where they are in tight contact with the violin top plate. Inspecting the pattern on the bottom of the bridge feet will reveal all. Ideally it will be inked evenly all over on both feet.
...Once the feet are properly fitted then the top surface of the bridge needs to be shaped for proper string clearance over the end of the fingerboard.
...After that, the bridge needs to be reshaped leaving the proper 'tuning' in place for the finished instrument.: