Wim Writes: >Wimblees@aol.com >To: Pianotech@PTG.org, caut@ptg.org >Subject: those pesky swings >We all know that a hammer is supposed to swing 4 - 8 times. Dear Wim, There are many technicians who don't use the swing method. The alternative is to use a gram gauge instead of swings for measuring flange friction: http://www.stanwoodpiano.com/hffguage.jpg Because of the decrease in hammer weight bass to treble, setting hammer flange friction to make equal swings across the keyboard creates a decrease in hammer flange friction from bass to treble as measured with a gauge. If you want to have uniform gauge friction of say 4 grams using the swing method, I would guess that 7 swings in the bass tapering down to 3 swings in the treble would do it for a medium strike weight... Here's why: Some observations... I just tested a flange on a hammer with a 10.0 gram strike weight. I measured with the gauge at a radius of 32mm which is the length of a Steinway or standard short flange. With 8 swings I get a friction of 2.5g. This particular flange has friction adjustment screws so I tightened them down to get 4 swings then re-measured the flange friction and got 7.0 grams. When I set the Strike Weight to 8 grams, gives 8 swings gives 2g. and 4 swings gives 4g. of gauged friction. So, in these cases, the 4-8 swing rule results in a wide range of variation with strike weight variations causing variations as well. Another variant is that when swinging, the flange is moved through an arc that is much greater than what the flange moves through when the part works in the piano. Sometimes, especially on older parts, if you gauge the friction through it's working arc, you will get a much lower reading than if you measure outside that working arc. The swing method can give false readings because of this. If we set the friction to produce 4 swings across the keyboard with say a half medium strike weight, we see that hammer flange friction will be 7 grams at note 30 and 4 grams at note 60. We could guess that the friction is around 8g at note 1 and 3g at note 88 for a drop of 5 grams across the keyboard. For each gram change of gauged friction we see a change of a gram in the friction weight (D-U)/2. When flange friction gauged to a uniform reading across the keyboard we normally see a drop of friction weight of about 4 grams from bass to treble. If we use the swing method we can add another 5 gram tapering of friction weight for a total of 9g decrease from bass to treble. So the swing method exaggerates the natural tapering of friction from bass to treble. If we look at a generic version of the old Steinway Down/Up specs by sections: 50/20 49/21 48/22 47/23 46/24 The friction weight is F=(D-U)/2: 15 14 13 12 11 Here we see the classic drop of 4 grams that is associated with uniform gauge friction in the Hammer Flange. These classic specs are achieved with a gauge friction on the hammer flange of 5 grams. If we exaggerate the friction tapering with the swing method we would see frictions sort of like this.... 18 15 13 11 8 So with down weights to spec the d/u would look like this... (U=D-2F) 50/17 49/19 48/22 47/25 46/30 The greater tapering of friction from the swing method exaggerates the difference in Up Weight from bass to treble. The Up Weight tapering is even more pronounced with uniform down weight. 50/17 50/20 50/24 50/28 50/34 Chew on that! As I said, if you want to have uniform gauge friction of 4 grams using the swing method, I would guess that 7 swings in the bass tapering down to 3 swings in the treble would do it for a medium strike weight... Cheers! David Stanwood
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