Dear Pianoexpert,
in the replacement of the key flange felt on a Schimmel upright piano, 114 cm high,
which thickness do you think is most suitable for the replacement? 1.3 mm?
Thank you
Started by
Pianoaccordatore
Moderator
Reply 2 by pianoexpert
- Posts
- 3,876
- City
- rocca di papa
When replacing the felt in Kasimir of the keyboard keybed mortises, one must start with the thickness of the pin. Once measured, cauls of the correct size are chosen (pin thickness + a tolerance). There are several types of cauls (small wedges that provide clamping during gluing). The crudest are steel clips. No good result can be obtained using them. Then there are nylon cauls, very precise, such that an intermediate larger size exists for the first gluing phase (on only one face of the mortise) and a final one, which holds both faces. Good precision. Then there are brass ones that are used hot. Extreme precision and obtaining perfectly "ironed" surfaces. Minimum friction and minimum key play in all positions.
Coming to the felt: once the right caul is chosen, one tries to insert the felt held by the caul dry without glue. The clamping must be such that it does not cause the key to fall, making it "dangle" by holding it by the caul itself.
Strict use of hot glue which does not penetrate the surface of the felt.
Generally, 1.2 - 1.3 mm is used in modern pianos.
The felt must not be placed too deeply in order to avoid excessive friction.