touch weight

[David C. Stanwood]

Newton,

Some comments on your recent post:

>Would measuring the weights at three or for velocities give an idea of
>inertia?  Inertia is a major consideration of drive head arms so you
>may have some information or ideas in this area already.

An increasing number of technicians find that they can control inertia
by choosing hammer weights that are compatable with given leverage ratios.

This means looking at Hammer weights and Shank Strike Weights before the
hammers are hung, or Strike Weights if measuring after the hammers are 
hung.  The trick is to know what leverage components work with  what hammer 
weights.  This is basic engineering 101.  If the rock is  too heavy get a
lighter rock or a stronger arm or both!  High ratio actions like 1:7 are
totally intolerent of hammer heaviness.  1:5 actions can handle the heaviest
hammers made.  Then there is all the stuff in between.

The most common mistake that techs make is to use a knuckle that is 15.5mm
out on the shank as the original parts were, then using a heavier modern 
weight hammer.  For Today's hammers the most succesful part is the Hamburg
style shank with the knuckle mounted 17mm out from the hammer center.

Leverage is made more complicated by the fact that key ratios vary from one 
Steinway to another.  I strongly recommend that any tech who is replacing
parts, learn how to use a standardized method of measuring key weight ratios
or key distance ratios and keeping notes on what key ratio works best with
which
part and hammer weight level.

Lack of attention to these details lends an aspect of "rolling the Dice"
to our work.  Take measurements and keep a notebook!!!!!

>The current practice is to remove the front most key weight then place
>a 20 gram weight on the key then set the down weight by moving weights
>back and forth on the key then using differing weights determining how
>much weight the key will lift, this gives the friction of the key. 
>Then use a set of up and down weights predetermined by friction and
>desired balance weight and cut a weight down until it will achieve the
>goal by placing it into the vacated hole.

Don't forget to always cross check the down weight.  As a rule of thumb,
if it's above 50 grams check friction.

David Stanwood