Touch Weight

[David Love]

Jim:

I agree with you generally.  But there are times when modest redesigns are
in order and to fail to consider them will often lead to bad results. 
While a thorough understanding of design elements will always give you a
better result, there are some simple ways to approach things if you don't
yet have that type of expertise that will often give you a better result
than what is there.  

An overall look at the action before it is disassembled can give you a lot
of information without taking the extensive measurements that Stanwood
suggests.  I do think it is important to adopt the balance weight as a
standard rather than simple downweight, but understanding that is not
difficult and is outlined well in one of Stanwood's articles in the PTJ a
few years back.  (You also mentioned the formula in you previous post.) 
)Measure the knuckle to center distance, a few sample hammer weights (try
measuring all the C's to give you a sense of the weight curve), the up and
down weights and look at the number of leads in the keys and their
placement.  That information will give you a lot with which to make
decisions about changes.  

If you don't have extensive knowledge, then the simplest changes that can
be made, if you think there is a problem with the action set up, will
involve adjusting hammer weight or selecting a knuckle-to-center pin
dimension that is different than the existing one.  If the old action
weighs off where you want it to and there aren't an excessive number of
leads in the keys, then you can try to simply duplicate what is there,
weighing the hammers and following the procedures you laid out in your
previous post.  

Without weighing the front weights of the keys it is difficult to determine
precisely what constitutes excessive front weighting, but as a general rule
no more than four in the low bass, three in the low tenor, two in the mid
treble and one in the high treble.  That's assuming they are placed toward
the front with moderate spacing between them.   If the leads are placed
back toward the balance rail, then you can add one more lead and probably
not get excessive.   If your desired hammer weights will cause you to have
to add more leads to achieve the balance weight you want, then consider
using a knuckle to center dimension that is 1 mm longer than the existing
one.  A move of the knuckle by 1 mm will usually change the BW by about 5
grams ( a longer knuckle to center pin dimension will also reduce friction
slightly).   Try a few samples to make sure that they will regulate
properly.   If you are unable to alter the knuckle dimension and your
existing hammers are producing excessive balance weights then you will have
to reduce the hammer weight.   Depending on the action leverage, a
reduction in the hammer weight by 1 gram will cause a reduction in the BW
of 5-6 grams, or it will allow you to take one 12 gram lead out of the key
from midway between the front of the key and the balance rail.  Not hard
stuff.  I use a balance weight range of 36 - 40 grams (lighter - heavier). 
While there are times when one might want to go lower or higher, I would
generally recommend staying in that range.  I default most actions to
around 38 grams.  Of course, be sure whatever you do that you test for
regulation with samples.  It is likely, however, that an action that
requires a modest number of leads to achieve a medium balance weight will,
by definition of action ratios, regulate properly.  

These sorts of simple design changes are routinely made and usually without
any problems.  I don't think technicians who aren't well versed in action
design need fear these types of changes.  Just sample things methodically
and take care to create a smooth hammer weight curve by whatever your
favorite tapering system is (mine is with a table saw).  Though I prefer a
more thorough approach as is offered by Stanwood methodology, you can get
good results making modest changes to the action without  all the platforms
and detailed formulas.  Just work carefully and think through cause and
effect before you glue it all together.  


David Love
davidlovepianos@earthlink.net


> [Original Message]
> From: James Ellis <claviers@nxs.net>
> To: <caut@ptg.org>
> Date: 1/2/2004 4:21:11 PM
> Subject: Touch Weight
>
> David Love's point is well taken, and I agree.  However, my previous post
> titled "Touch Weight" was in response to Paul Legard's request for a
simple
> routine to follow that would produce good results.  From reading some of
> the posts on this list, it seems to me that many technicians out there do
> not have a sufficiently clear concept of action dynamics to attempt any
> sort of re-design of an existing action.  Hammer weight (mass) is dictated
> by string mass and the sound one wants to produce, but constrained by the
> mechanical limitations of the system.  John Hartman's description of
moment
> of inertia is correct.  You must look at the entire compound lever system,
> but it all boils down to static weight, leverage ratio, time, mass, and
> distance traveled.  No matter how you describe it, the basics remain the
> same, and it is not just "theoretical".  It is very real, and provable.
> The simple point I am making is:  If you really know what you are doing,
go
> ahead and re-design the action.  If not, don't do it.
>
> Sincerely, Jim Ellis
>
>
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