Measure friction weight was: Weighting upright keys question

[Porritt, David]

Julia:

 

Keep in mind that the weights from some suppliers are not accurate.  I
bought the little gram weight set from a major supplier and found them
all to be heavy (fortunately).  I simply drilled holes in each weight to
remove the excess and calibrated each one.  Some of the weights have a
lot of holes!  Of course to do this you'll need a good scale properly
calibrated and capable of reading down to at least 0.1 gram.

 

dp

 

David M. Porritt, RPT

dporritt at smu.edu

 

From: pianotech-bounces at ptg.org [mailto:pianotech-bounces at ptg.org] On
Behalf Of Fenton Murray
Sent: Sunday, February 17, 2008 7:49 PM
To: Pianotech List
Subject: Re: Measure friction weight was: Weighting upright keys
question

 

Julia,

To do this work you'll need a set of gram weights. They are for sale at
most of the supply houses. With these weights you can place an exact
amount on the end of the key, say 50 grams, with the damper pedal
depressed (important), see if the key will fall to the point of let off.
We are only concerned with the travel of the key from it at rest up
position down to the point of let of. The lowest amount that will cause
the key to drop (with the damper pedal depressed) is the down weight.
Then depress the key to let off and place an amount on the key, the most
the key will lift up to it's at rest position is the upwieght, maybe
around 25 grams. A little taping on the key bed to get things to move is
OK. You need to try some of this before trying to figure it all out.
Once you've spent some time with it you'll find it opening doors to a
higher level of action work. There is lot's to understand. Read the
Stanwood articles in the PTJ, I think they were early '90s. Use the PTJ
on CD.

Fenton

	----- Original Message ----- 

	From: KeyKat88 at aol.com 

	To: pianotech at ptg.org 

	Sent: Sunday, February 17, 2008 3:22 PM

	Subject: Re: Measure friction weight was: Weighting upright keys
question

	 

	Greetings,

	 

	             So how do I start making measurements to see what
weight a key(s) neeeds?  How do I measure friction? I am guessing that I
should start  by measauring the the foot-lbs (or cm-grams?)  inertia it
takes to start the power stroke at the wippen heel/foot. Then I have
measured my fricion...right? Then I can do the uw/dw calculations.

	 

	Julia 

	Reading. PA

	 

	In a message dated 2/16/2008 11:27:46 PM Eastern Standard Time,
fmurray at cruzio.com writes:

		Given a certain friction in the piano we are going to
want to set up something like maybe a downweight (dw) of 50 and an
upwight (uw) of 25. All numbers in grams. This is assuming a friction of
12.5.

	
	
	

	
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