Chickering rebuild -- touchweight.

[David Stanwood]

Hi Gary,

So the point is that you want to get your balance weight down and make a 
lighter action.

There are four ways:

1. reduce friction weight
2. reduce hammer weight
3. Increase front weight
4. Increase leverage

Some comments

>So far I have re-bushed the keys

Did you put try Teflon in the bushing felt?  Friction coefficient between 
felt and metal is high.  Dry lube prevents wear but it's no substitute for 
nicely eased keys. Friction weight numbers would indicate if high friction 
is contributing to your heavy touch.  What kind of friction weights do you 
come up with?  If they are high zone then Key Friction Weight would be the 
first place to look.  (this method is published in the Journal) If that 
checks out then hammer flange friction would be next, etc...  The numbers 
tell you where to look..

For Friction Weight zones refer to:

http://www.stanwoodpiano.com/f-zones.jpg

>I plan to cut a little more weight off of the hammer tails

This is a weight modification.  Are your hammers heavy, medium, or light? 
Strike weight evaluation would guide your decision here.

For Strike Weight zones refer to:

http://www.stanwoodpiano.com/sw-zones.jpg

>Hence, it looks like a reweighing of the keys is in order.

Try weighing off some sample to say a 40 BW and see what kind of front 
weights you come up with.  If they are below the front weight ceiling then 
your probably ok..  (Front Weight Ceiling was Published in the Journal, I'll 
post it if you want….)

If it takes too much front weight to get even a 40 BW and your hammers are 
not too heavy then you have a leverage problem and the capstan line has to 
be moved towards the balance rail.  There are two rules to follow:

1. See that the capstan/heel contact point is close enough to a line between 
the wip center pin and the balance point of the key that there is minimal 
rubbing between the capstan/heel.

2. Don't move the capstan so far as to create the need for unacceptable deep 
dip with a standard blow distance.  0.420" with 1.75" blow would be my 
extreme for this.

Determining the average level of Strike Weight ratio will tell you if your 
leverage is ok.  If the strike weight ratio is above 6.0 then any strike 
weights above mid medium zone will be trouble...

All the above assumes that you arc geometry is acceptable.

Who said touch weight was simple?

By the way, the Touch Designer Toolkit is nice but you can take these 
measurements jungle style with home made jigs as shown in the June 1996 
article "The New Touch Weight Metrology"

David C. Stanwood


>From: Gary Rondeau <grondeau@efn.org>
>Reply-To: pianotech@ptg.org
>To: pianotech@ptg.org
>Subject: Chickering rebuild -- touchweight.
>Date: Mon, 29 Jan 2001 11:50:58 -0800
>
>Dear List,
>
>I am rebuilding a 5'6", 1907 Chickering. So far I have re-bushed the
>keys, replaced the hammers with new shanks and knuckles and replaced all
>the keybed felt.  I have played on it for a year and am fairly happy
>with the results except that the touch is a bit heavy.  The balance
>weight averages about 50gm across the keyboard.  I plan to cut a little
>more weight off of the hammer tails, but there is not much more to be
>gained their. Hence, it looks like a reweighting of the keys is in
>order.  Presently, there are keyweights in the front of the keys on keys
>1-50, and behind the pivot from 50-88.  My question is this -- If I am
>going to add front weight to the entire keyboard, what should I do up in
>the treble?  Should I remove the old keyweights behind the pivot first?
>If I don't do this, it seems that the inertial weight will climb in the
>treble since there will be weights on both the front and back.  Any
>suggestions on removing keyweights and plugging or not plugging the
>holes?
>
>Thanks,
>
>Gary Rondeau
>Eugene, OR
>grondeau@efn.org
>
>
>

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