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A friend has a Yamaha ER10 piano that had become in need of tuning. That seemed to present an opportunity to explore the what, why and where of piano tuning.
The tuning exercise went quite well, it took a few hours, no broken strings or other damage, the piano was in tune and held the tune state generally well over the next months.
However, during the tuning job, it became apparent that one key was about 1.5mm lower than its neighbours which prompted further examination. The key was stiff and did not return to the full up position, although it would do so with a little downwards pressure applied to the back of the key. A wider looks showed that quite a few keys were a little stiffer than most.
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The next step was to remove the action, which was not difficult, although impeded by the transit screw that seems had not been removed at installation, see Fig 1. One wonders whether the action was ever removed during previous maintenance visits by technicians.
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Removal of the action gave better view of the keys and it was noticed that many of the capstan screws were quite corroded, see Fig 2.
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Removal of the worst sticking key revealed the cause, severe corrosion of the balance rail pin in the region of the lower part of the key timber. This corrosion made removal of the key quite difficult. Fig 3 shows the balance rail pins after removal of the keys.
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Fig 4 shows the corrosion on a typical balance rail pin and capstan screw. Note the balance rail pin is in good condition at the left end where it was embedded in the balance rail, and above the top of the key. The worst corrosion is in the region of the proximity of the timber at the base of the key.
The capstan screw is rusted severely where it was in intimate contact with the key timber, and is in excellent condition around the head and flats.
Before embarking on repair, it is worth considering why or how this happened to a 20 year old piano by a reputable manufacturer.
The piano is located in an inland dry climate, the room and house containing it are not particularly humid, humidifiers and evaporative air conditioners are not used, there are no indoor plants in the room with the piano.
There was a little dust under the keys and in the base of the piano, there was no sign of pests, no mouse dirt or pee stains, no signs of water.
The strongest hint is that the corrosion seems to be localised to the metal parts in contact or proximity with just some of the planks that were glued up into a board to make the keys. The colour of corrosion products might give a hint to the chemical reaction that occurred, and possible source of the reactants. Fig 2 shows corrosion of the capstan screws in the whiter timber, similar was observed over the whole keyboard and with balance rail pins. The whiter timber seems to support corrosion more than the darker timber, perhaps it is even reactive and caused the corrosion. Reactive timber could be natural, the result of a treatment process or even salt acquired when logs are transported or stored in brackish or salt water. The observations raise a question of quality control in Yamaha's manufacture processes.
The piano needed replacement of some balance rail key pins and capstan screws. The balance rail pins were slightly smaller at 0.139" than the common 0.146", so genuine replacements were sought. Capstan screws appeared in many after market catalogues, but in the end, were difficult to source, so genuine parts were sought. Genuine parts were much more expensive than after market parts, and buying parts from Yamaha meant an inquisition about the origins of the piano.
The Yamaha replacement parts were a little different to the original parts, the replacement Yamaha balance rail key pins were brass as against the original plated steel. The replacement Yamaha capstan screws were a different thread, and had a hex face for the adjustment tool.
The rusted capstan screws were removed. They generally tore up the timber around the thread a bit, and one key split. The split key was repaired by gluing with hide glue. The capstan screw holes and balance rail key pin holes were blown out with compressed air and the timber in intimate contact with metal was doused with WD-40 to buffer the metal from potentially reactive timber. It was important that no liquid got onto the felt. Where the replacement capstan screw was a loose fit in the hole, the hole was packed with shaved toothpick to provide sufficient purchase to be stable over time.
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The rusted balance rail key pins were removed by gripping them in a drill chuck (not attached to a drill) and rotating them whilst pulling them upwards. They all came out with ease. The felt and paper punchings were blown out with compressed air to remove rust particles. (I had purchased a full set of after market felt punchings, but they were not needed.) The new pins were driven in, I think the technical term is "pounded in". Figure 5 shows a tool that was made for driving the balance rail key pins straight and to a uniform depth. The tool was made from 10mm mild steel, and worked a treat. The felt and paper punchings were restored.
The key area was vacuumed out and the keys were inserted. The keys were levelled by adjustment of the balance rail punchings, and the key dip checked. A supply of paper punchings was procured to support the key adjustment process.
The capstan screws were adjusted.
The piano was give a quick tune, and appeared fully operational. The state of the metal parts in contact with key timber will be monitored over time, which will mean periodic removal of the keys for inspection of the balance rail pins, front rail pins, and capstan screws.
| Version | Date | Description |
| 1.01 | 22/09/2006 | Initial. |
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| 1.03 | ||
| 1.04 |
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