Although I have made quite a few sound-board panels using AR glue (see above) this will be my first using hide glue, so I'm going to approach it rather timidly, and joint and glue the panel one piece at a time. Otherwise, as I generally work alone, I would construct a heated table, if I were not too lazy, and proceed at leisure. The panel for the Erard has only seven pieces, the same as the original, so this method won't take very long.
 Above, an intermediate step. The final two pieces, you can also join them in pairs, as shown below.
The panel rough trimmed, and cleaned up, a bit, but not leveled, the thickness at this stage is around 10 mm. Final thickness will vary from 5.5 to 7 mm, before final thicknessing the panel will sit in the hot room for two weeks and shrink down. The hot room is set at 26% RH.
In gluing up large panels out of individual boards, good woodworking practice usually dictates that heart wood should be joined to heart wood, and sap wood to sap wood. In actual practice, however, matching run-out overrides this rule. If the wood is split, or properly saw, which it seldom is, and there is little or no run-out, then boards from the same flitch may be book matched, which evens out the shrinkage at the glue joints, as well as allowing smoother color changes across the face of the panel.

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