Spine, Bentside & Tail
The rim is made of three distinct parts: the spine, the tail, and the bentside.
- Spine – The long straight portion of the rim that is on the left (bass) side of the piano
- Bentside – The curved portion of the rim that is on the right (treble) side of the piano. This distinctive shape is a result of the treble strings being shorter than the bass strings.
- Tail – The portion of the rim that is opposite the keyboard. On modern grand pianos, the tail is curved to match the bentside. Tails on harpsichords and many early pianos were usually straight across.
Construction of the Rim
The shape of the rim is derived directly from the wing-shaped harpsichord. Cristofori used the case of a harpsichord to build his first pianos, and the shape has now become the identifying feature of the grand piano. The rim is made of many thin sheets of wood, called veneers, which are glued, or laminated, together (similar to plywood). If the rim were made of one solid piece of wood, the wood could expand and contract across the grain due to changes in the humidity levels. Over time, this movement of the wood could result in the warping or cracking of the rim. By laminating many thin pieces of wood together and alternating the direction of the grain in each layer, the chance of this harmful expansion and contraction is virtually eliminated. The top (or outside) veneer is usually made of mahogany, and is finished to match the whole piano case. In order to create the distinctive shape of the piano, the long laminated rim slab is put into an iron press, and formed into the proper shape. The rim is glued together, and held in place by clamps until it dries.