Rim Bending Process
In a unique method used by Steinway for over a century, the inner and outer piano rims are bent into the shape of the rim as a single continuous piece. Before Theodore Steinway developed and patented this method in 1878, rims were made of separate pieces held together with joints.
All Steinway grand pianos are built upon rims made entirely from straight-grain hard rock maple and 2 face veneers. The number of laminations varies according to model:
- 12 for the Model 'S'
- 13 for the model 'M'
- 14 for the model 'O'
- 15 for the model 'A'
- 16 for the model 'B'
- 18 for the model 'D'
Each lamination is 3/16 of an inch thick, and is positioned so that the grain is set horizontally. Horizontal setting rather than the cross-grained (the technique for plywood) used by some makers of grands, improves tonal projection by an estimated 47%.
All Steinway grand piano rims are continuously bent in presses designed and built by Steinway. Together, the inner and outer rims for one united rim. Moder high-frequency gluin welds together the laminations.
The single inner and single outer rim is constructed from hard rock maple. Steinway invented this process which permits the soundboard to be built into the rim. No part of the sounboard is forced down. The Steinway rim provides the solid foundation for proper stress-free mounting of the soundboard. The purpose of this construction is to provide sigular tonal resonance and construction stability.
After being guled the rims are removed from the presses, they are chalk-dated and stored upright in a conditioning room. There they relax from the tremendous shock of being bent. Rims remain in the conditioning room between 10 and 16 weeks depending on the thickness and size. The room's temperature is set at 85 degrees Fahrenheit; and the relative humidity is 45%.
In terms of design, materials and workmanship, the Steinway system of rim bending maintains ultra-high overall string tension, as well as down-bearing and side-bearing, almost indefinitely.
The method of rim bending was invented by C.F. Theodore Steinway. It became U.S. Patent no. 229298 on June 22, 1880. The original patented process is strictly adhered to today.
When Steinway’s rim-bending patent expired years ago other grand piano makers began to employ the method. Over the years, however, nearly every manufacturer discontinued the production of a single united rim in favor of two seperate rims (inner and outer). The reason others choose the two-rim system – it’s inexpensive.