The instrument received some additional reinforcement in two forms. Firstly, several braces were attached along the full width of the bottom. The stress from the strings pulling on the bentside liner, if one thinks about it, is transferred from the notch at the top of the knee down to the base of the knee, and might cause the bottom to buckle somewhat. Four braces made of Douglas fir, which is strong and stiff, help keep the bottom flat to resist this.
Secondly, a couple of "flying buttresses", also out of Douglas fir, were wedged in between the bentside liner and the bottom. These required some rather complicated compound cuts on each end, which my father ended up calculating on paper. Two of these go at the bass end of the bentside, where string tension is high, and one goes in the treble near the cheek, which is a problematic area in many harpsichord designs: the soundboard often cracks in the treble and creeps into the register gap. Since the compound cuts were close but not quite perfect, I secured the buttresses with epoxy, which has reasonable strength across gaps (most glues are strong only when the joinery is tight).
Lastly, the joints between bentside liner and knees were reinforced with #8 wood screws as extra insurance, and dowels secured the far end of the spine and bentside liners to the corner blocks at the tail of the instrument.
I've inscribed a dated note marking the completion of this stage on the back face of the lower belly rail.
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