Finishing the registers

The four registers need to be cut down in length and assembled together in pairs. Each pair is held together with spacer posts, which have a profile designed to fit into the grooved underside of the upper register:


These posts go not into the register slots, which are for the jacks, but in between them.

First, the registers are stacked in pairs, and to make sure the slots are vertically aligned between the two, blocks sized to fit snugly in a register slot are slipped through slots at opposite ends:


Spacer posts are installed into the bottom register at 5 places, and the entire assembly is drilled at these locations with a #54 drill bit. The hole depth is controlled so that the bit passes through both registers and makes a small dimple in the post. It is not possible to drill much further because the drill bit is pretty short.

Next, the assembly is taken apart. The dimple mark is used to align the bit correctly and drill the spacer posts vertically all the way through. The holes in the registers are then enlarged with a 5/64" bit.

This process creates holes for #2-56 machine screws in the spacer posts that are accurately aligned with clearance holes in both registers. The spacer posts are tapped with the appropriate tap from both ends, and all the components are temporarily screwed together with 3/4" brass machine screws to check the configuration.

Each register pair hangs from a pair of gap spacers which span the gap between the wrestplank and upper belly rail:


In other harpsichord designs, these little struts keep the gap from closing up due to the tension of the strings. Italian harpsichord designs don't need this kind of help; if they do, the design is fatally flawed. I'm using them just to hold up my registers. The upper register lies on top of the gap spacers and the remainder simply hangs down inside the gap, like this:


Each register pair is installed by screwing the spacer posts to the lower register and pushing it up into the gap from the back of the keywell. Then the upper register is slid sideways into the instrument through the spine window, pressed down onto the spacer posts, and screwed in place.

One final detail is this walnut cover plate for the spine window: