[pianotech] Grams, swings and centre pin sizes

[John Delacour]

At 12:30 -0600 8/1/09, Ron Nossaman wrote:

>I agree too, but where's the alternative measurement process that 
>produces a measurement in the proper terms?

Well a good engineer or mathematician could actually convert swings 
to grams force/millimetres but as you rightly say:

>...it's not absolute measurements that are needed in practical 
>application, it's a reliable means of comparison within a limited 
>range

My main point was to demonstrate the inexactitude of the "gram" 
method used indiscriminately, firstly because n grams in the screw 
hole of one flange will indicate a different friction from n grams in 
the screw hole of different flange, and what we are aiming for is a 
certain degree of friction.

The swing method is a quicker and more reliable measure and I'd say 
that starting the swing with the shank horizontal and a note 50 
hammer head, five half-cycles is about right, that's to say that the 
head will cross the lowest point on the arc five times.


>  My "standard" is a clip clothes pin, and I swing grade sets before 
>installation. I put the tight centers in the treble, because that's 
>the area that needs firm centers for tone production. The looser 
>centers go in the bass, because that's where the hammer weight 
>problems are, and I don't want any more center produced friction 
>than necessary.

That sounds like new shanks with flanges attached straight from 
Renner or wherever.  In the sort of work I do I am usually restoring 
the originals, which must remain in roughly the same order, and I 
(rebush and) recentre with the old hammers still attached, so the 
swinging (if I were to do it) is done as part of the recentring 
process: broach, tallow, swing the hammer holding the pin by its flat 
end in the cutters, broach more if needed, push in the pin using the 
cutters and cut flush.  I aim for equal friction throughout the scale.

So much for hammers.  How to swing for a grand jack?  For other 
centres than hammers, I recommend to learners the little balance I 
posted in my last message.

JD