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The key frame is bedded to the key bed by tapping along each rail in turn. Only a properly bedded key frame can avoid audible knocking during heavy playing. It is esential that the key frame is bedded in accurately as it is the foundation for the regulation of the action.
The keys are then placed on the key frame in the piano and back weighted. The correct height is set for the naturals first and then the sharps using a straight edge. Height is adjusted by adding and removing card and paper washers.
With the action in place all the parts are accurately aligned and the blow distance set. This is the distance from the hammer nose to the string. Trials are accurately set in the piano, the remaining hammers are then lined to these.
Correct set off adjustment is essential to prevent the hammers from fouling the strings. It is the point when the hammer disconnects from the playing mechanism. It is graduated throughout the compass off the piano, as lower notes have longer strings that move more when struck.
The touch depth is adjusted by placing card and paper washers under the front touch baizes, A special block is used as a guide throughout this process. The correct and even after touch must be acheived throughout, which requires expert judgement and feel.
Once the string has been struck the hammer rebounds and falls under gravity. It is caught by the check head, the position evenly set across the whole compass to provide smooth and reliable response to all playing styles.
The graduated repetition springs are expertly adjusted to provide an even and responsive touch. The spring strength is related to the hammer size and weight. The spring tension must be exactly right to produce the perfect feel in repetition play.
Lead weights are removed and added to the front of the keys to meet manufacturers specifications. Both down weight (the force needed to depress the key) and up-weight (the speed the key returns) are adjusted to produce the perfect touch for the pianist.
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Voicing starts even before the hammers are fitted to the shanks. Each shank is tapped against a hard surface to determine its pitch. The lower pitched shanks are used in the bass, the higher pitched shanks used in the treble.
Only an expert can produce the perfect shape of hammer once fitted to its shank. The manufacturing process causes "cups" or "ears" to be formed. Shaping eliminates these defects and ensures an even shape for the finest sound production.
The hammers are individually faced to the strings. Each hammer is held to the strings and the nose expertly shaped so that each string is struck at exactly the same time. This work requires great patience and experience.
"Doping" - the application of a special lacquer - is nescessary to correct tonally weak hammers. This is a delicate and highly skilled technique requiring great expertise. It does, however, produce the required results - in the right hands.
The skilful use of needles adjusts the tension and compression that exist within a piano hammer. Again, this is an expert technique, enabling a skilled technician to create a pleasant even tone throughout the compass of the piano for all playing conditions.
The final stage of voicing starts with delicate shaping the hammers with fine paper. This reproduces the correct hammer shape, lost during the needling process. The hammers are then needled to obtain an even tone throughout when the una-corda pedal is used.
Barry Caradine Piano Specialist
Bull Lane Ind Est, Acton, Sudbury
Suffolk CO10 0BD East Anglia
+44 (0) 1787 312231