shank strike weights

[Porritt, David]

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Jon:

=20

I understand the different heights of the knuckles and the effect on the
leverage.  Do you also find much disparity in the knuckle placement -
i.e. are all 17mm knuckles exactly that far from the center pin or do
you get a range?  That could also make quite a difference.

=20

dp

=20

David M. Porritt

dporritt@smu.edu

________________________________

From: pianotech-bounces@ptg.org [mailto:pianotech-bounces@ptg.org] On
Behalf Of Jon Page
Sent: Tuesday, November 15, 2005 6:59 AM
To: pianotech@ptg.org
Subject: shank strike weights

=20

> What is the benefit or what <is> the noticeable difference of
measuring

>the knuckle, besides making the let off buttons nice and even and look
good?

=20

I first started measuring knuckle and shank thickness because of what I
would

call a poorly installed set of knuckles and was surprised to find such a
wide disparity. Measuring the thickness of many shanks proved to have
negligible differences so the differences were in the exactness of
pressing the knuckle in. I measure from the top

of the shank to the bottom of the knuckle.

Last year I posted about a knuckle caul press for this concern.

=20

Subsequent sets measured to have differences between .5 and 1 mm (.020 -
.040")

within the set. I maintain a window of .25 mm (.010"), that's +/- .005"
(.125 mm) from

the average overall shank/knuckle height. I place the bulk (average) of
the shanks

in the center and the +/-'s at the extremes. A more level let off button
line was just an interesting result.

=20

Action geometry is affected by the size of the knuckle so anything one
can do to

bring uniformity benefits the action.  Priority for shank selection is
matching shank SW

to hammer weight with knuckle height second.

=20

Ultimately the best scenario, inertially speaking, would be to graduate
the weight of the hammer heads themselves and group same-weight/knuckle
height shanks. But most hammer sets are

so erratic in individual weights that it takes invasive procedures to
have them comply.

=20

Matching shank SW to hammer weight has proven to require minimal
intervention for

a smooth SW curve.

=20

First, I bore and taper the hammers.

Weight them and plot them on a graph.

Select shanks accordingly and install them on the rail. (# on underside
next to knuckle)

Hang hammers.

Remove h/s/f from the rail.

Cut the protruding shank off with a band saw and rough cut an arc.

Set up fence to trim tails on disk sander to even length.

Arc tails.

Weigh SW and plot on chart

Adjust SW

Install h/s/f on rail.

=20

I sounds like a lot of work but it goes fast. I like to arc the tails
after hanging the hammers

to produce a nice finished edge. I also ease the edges (sides and
bottom) of the tail molding

to remove the sharp corners with a file.

=20

--=20


Regards,

Jon Page


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