Pianotech

  • 1.  Grand hammer shank flange pinning torque

    Posted 08-17-2023 20:12

    Perhaps the most authoritative document I have on flange bushing Renner's Technical Manual "Renner Flange Bushing Cloth" clearly states that hammer shank flanges should be 2-5 grams measured 23 mm from center pin.   No difference indicated for 1 - 88 note.

    Yet I see numerous comments in various technical forums that measuring flange torque with a torque gauge is "inaccurate".  But people making this comment never say why, usually advocating for the swing test (which will clearly result in a graduated torque result, or at least a stepped on if the target swing is changed at various points across the 88 flanges).

    Thoughts on torque gauge accuracy and having the same target torque across the full keyboard appreciated.

     Thanks,



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    John Woodrow
    PENSHURST
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  • 2.  RE: Grand hammer shank flange pinning torque

    Registered Piano Technician
    Posted 08-17-2023 22:07
    On a number of occasions, I've measured the torque on a flange with a gauge, both uprights and grands, where they were on the tight side, (more than 5 or 6 grams), but the hammers swung the right number of times. I've also had the reverse happen. 

    On grands, I like to lift the shanks all the way up with a stick, and then make them drop. Any flange hammer that drops at a 11 o'clock or less is too loose. And hammers that don't drop until 9 are too tight. I've also tipped the stack upside down and swung the hammers. Loose one will continue to swing more than 5 times. Tight ones swing less than twice. 

    Upright flanges are a little more difficult to test on the action frame. I usually have to remove each one to do the swing test. I've seldom used a gauge on them. 

    Where I do use the gauge is on upright wippen flanges. It's hard to do a swing test on them. 

    Wim





  • 3.  RE: Grand hammer shank flange pinning torque

    Registered Piano Technician
    Posted 08-19-2023 11:53

    Hammer flange friction is a tradeoff between rigidity for clean tone, avoiding "fly away" for pianist dynamic control, and minimizing resistance that causes fatigue.

    Does a bass hammer need more or less friction than treble? Debatable.

    I make them all the same using a Correx spring gauge and a jig to maintain geometry. My tolerance for hammer flanges with wool bushings is 2.5 to 3.5 grams.  Wip flange 1 to 4, jack 1 to 2, rep lever 4 to 7. WNG style "plastic" bushings allow less friction (maybe 2 to 3 grams target) while maintaining tone because they are more rigid. I don't go much lower because it would impact touch control and feel too different.



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    Greg Graham, RPT
    Brodheadsville, PA
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