Touchweight query

[Farrell]

Keith wrote:

> Terry & Keith R, I agree of the importance of key bushings. I would 
> be interested, Terry, how you manage to precisely measure key bushing 
> friction, though.

>From David Stanwood himself, here is his explanation:

Terry,

I published the method in the PTG Journal in my atricle:

"Standard Protocols of the New Touchweight Metrology"
PTG Journal February 2000

Excerpt:

"The new measurement called Key Friction Weight (KF) tells us precisely how 
much of the Friction Weight is from the key bushings. Place the key on the 
front weight jig and follow the protocol for measuring negative Front Weight 
(FW).  With the key on the jig, place temporary weights on top of the key 
and slide them back and forth until a position is found that makes the Front 
Weight (FW) zero.  Then, without disturbing the position of the temporary 
weights, place the key back on the key frame and push the back of the key 
down onto the back rail cloth. Then find the minimum amount of weight placed 
on the front of the key at the Measuring Point that causes the key to drop 
(Fig 8).  Another way is to place the key on the frame and attach a key 
leveling lead to hold the back of the key down. Then measure Up Weight and 
Down Weight (with stack off) and apply the formula (DownWt - UpWt)/2.  The 
value found is Key Friction Weight (KF)."

I usually do an alternate procedure that I find much faster and "close enough". It is basically the same thing David does, but just a bit less accurate, but much faster (for me anyway). I start with the stack off the keyframe, but keys on. Just add appropriate weigh to the back of the key so that the key balances. Then take a small weight, one or two grams and place it alternately on the front and back of the key and see that it goes all the way down in the front and the back. Very easy to see whether you are down to one or two grams friction. Like I say, David's method would be a bit more exact. If you take an action where you have not set balance weights equal, you will find that you are changing the amount of weight added to the key for balance with every key. When you do this to a set of keys where you have set the balance weights equal, you can jump from key to key very quickly with the same stack of weights, just moving them a tiny bit. It's a neat way to observe what magic you have done to the keys!

Terry Farrell


  
----- Original Message ----- 
From: <kam544@flash.net>
To: <pianotech@ptg.org>
Sent: Sunday, June 30, 2002 11:47 AM
Subject: Re: Touchweight query


> >...My thought is the key bushings. Uneven wear causing the extra 
> >friction.  Try
> >some protec on the offensive key bushings. Just a guess.
> >Keith R.
> >
> >...either too high or too low.  Double check all friction points again and
> >check pinning in the hammer flange... David Love
> >
> >  ...If you have not precisely measured key bushing friction in each 
> >key, I recommend that be done. You may be surprised.
> >Terry Farrell
> >
> >...As far as things to look directly for, in addition to what Dave 
> >has pointed to
> >I would look at any slight differences in the angle the knuckle is 
> >glued to the
> >hammer shank... a very small angle difference can mean a lot really...
> >suprisingly so. Same thing about the capstan.
> >
> >...Also... do any adjustments in BW with whippen assist springs 
> >disconnected if
> >they are present.
> >RicB
> 
> Keith, David, Terry, Richard, List,
> 
> I certainly appreciate your thoughtful replies. At least, I am 
> reaffirmed that I was not amiss on the fundamental concepts.
> 
> In brief I wasn't looking to achieve exactness as much as a closer evenness.
> 
> A few things:
> Richard, there are no wippen assist springs. Also, I did investigate 
> the knuckle relation and actually altered it to see what difference 
> it might make. And I measured the capstan relationship as best as 
> possible.
> 
> Terry & Keith R, I agree of the importance of key bushings. I would 
> be interested, Terry, how you manage to precisely measure key bushing 
> friction, though.
> 
> Anyhow, as it turns out, and I really don't wish to admit it, but 
> hammer flange repinning is the culprit. On a fluke I applied Protek 
> CLP to the flange bushings and the DW dropped immediately.
> 
> Observing hammer swings did not reveal this and the hammer flange 
> appeared to drop of its own weight. Because of that I dismissed that 
> area completely.As I am discovering, this older Knabe grand requires 
> no resistance whatsoever to achieve the touch that I am desiring.
> 
> t's quite amazing all in all as opposed to say, some of the Steinway 
> resistance guidelines.
> 
> Thank you all for for your contributions.
> 
> Sincerely,
> 
> Keith McGavern
> Registered Piano Technician
> Oklahoma Chapter 731
> Piano Technicians Guild
> USA
>