While... I don't see how chalking the tail of the hammer can show us anything as the chalk will depose on the backchecks in any case during the checking. I believe the usual method to check clearance and security is good enough (and even very secure if on use a bit more force). this said The hammer rubbing on the check is felt while playing the note (once we are suspecting it or if we compare with a corrected regulated one). But indeed the 2 mm rule is certainly also a security measure by some aspect. Then, let's say also that different type of tails and bachecks may be addressed differently, that is why it seem important to me to understand the basic concept underlying the process. best Regards. Isaac -----Message d'origine----- De : pianotech-bounces@ptg.org [mailto:pianotech-bounces@ptg.org]De la part de Richard Brekne Envoyé : mercredi 18 août 2004 19:06 À : Pianotech Objet : Re: back check, a magical mystery tour. Grin... Stephen... this is the second time in a row you struck the exact chord that brings an appreciative smile to my innards... :) This time its directing us towards the obvious... common sense as it were. This explanation doesnt have a lot of sensuality to it... but it does show some promise of being in the right ball park. Stephen Birkett wrote: > We've seen quite a few 'second-tier' hypotheses - as Ric says, sexy > explanations - for the backcheck phenomenon. These things obviously > need to be examined experimentally, but a small dose of Occam might be > a good thing first. I'm thinking something is causing this that occurs > before the string impact. The obvious candidate is interaction between > the backcheck and the hammer tail as the hammer heads toward the > string. Backcheck clearance is supposed to be pretty tight, and I've > seen enough examples of slight catching on the check as the tail goes > up, enough that power is lost without it being obvious. For a given > action configuration, this effect doesn't occur for all blows. It's a > function of various action parameters, including softness of the > whippen cushion and other felt contacts, hammer shank flexibility, > tail geometry, and so on, as well as the type of touch applied to the > key. Lowering the check to achieve the magic 2mm separation may very > well ensure adequate clearance in all cases. > It may very well indeed... especially when the other back check parameters are adjusted correctly. > It's probably possible to check this on a "dud" key before and after > making the adjustment of backcheck height, even with just a bit of > chalk on tip of the key tail. Static clearance of the check/key tail > is certainly no guarantee of dynamic clearance. If it's too subtle for > chalk it will need some targeted experiments with high speed images to > investigate properly. > A good suggestion.. and easy to carry out... most certainly at least some what revealing. I'm a gonna give this one a try :) > From the current discussion, it seems the effect is also apparent if > backcheck clearance height is too much more than 2mm, and the > explanation above doesn't address that of course. To those who've had > good results with Andre's technique (including Andre himself), in > practical circumstances how often do the checks have to be lowered vs > raised? > Well.. lets see...if the back check is too high or too low.. then it has to be moved in the lateral direction and its angle has to be changed to maintain the same <<static>> check height and holding strength. So maybe.... the 2 mm simply describes the optimum distance for these other two directions to also be at their most efficient ?? As far as how often checks need adjusting. Hmm... you'd be suprised how varied back check height is off the factory line... even in pianos like Yamaha where <<precision machines>> are specially made to do the job. Then there is the hammer change job done by the tech down the street...... grin.. In short... it happens often enough that they need addressing. > Stephen Cheers RicB _______________________________________________ pianotech list info: https://www.moypiano.com/resources/#archives
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