Touch weight(Inertia)

[Ed Sutton]

Yes, but remember you can get the same frontweight with a small weight close to
the front of the key, or a larger weight close to the balance rail.  I believe it
was Joseph Hoffmann who realized that larger weights close to the balance rail
produced less inertia than smaller weights at the front.  And in particular one
would want to have an even progression of inertia from key to key, as well as an
even progression of front weights.

I believe this is the logic behind Vince's post.

Is there anything more delightful than piano technology?

Ed Sutton


----- Original Message -----
From: "David Love" <davidlovepianos@earthlink.net>
To: "College and University Technicians" <caut@ptg.org>
Sent: Friday, December 19, 2003 12:21 PM
Subject: Re: Touch weight


> The easiest way to use this stuff is by algebraically manipulating
> Stanwood's equation of balance to isolate certain variables and then plug
> in the appropriate matches from his published charts.  You can get these
> charts from his website: www.stanwoodpiano.com
>
> For example:
>
> The equation of balance is:
>
> BW + FW = (KR x WW) + (R x SW)
>
> BW = balance weight
> FW = front weight
> KR = key ratio
> WW = wippen strike weight
> SW = strike weight
> R = strike weight ratio
>
> The most useful algebraic manipulations are
>
> R = (BW + FW - (KR x WW))/ SW
>
> and
>
> SW = (BW + FW - (KR x WW))/R
>
> The procedure is to first  take sample measurements to determine what R is
> for the existing action.  You will need a platform and a gram scale for
> this.
>
> By using Stanwood's published charts of FW maximums and SW zones, you can
> then input data to determine what SW curve will work best for a given
> action (R) based on targeted BW and FW maximum.  You can do this for any
> sample note and extrapolate the rest of the SW curve from there.
>
> For example.  If your action yields an R of 5.5 by sample measurement, you
> can determine the maximum SW for that system from a sample note.  If we use
> note 40, for example, the maximum FW (according to Stanwood charts) is 30
> grams.  If your targeted balance weight is 40 grams, then simply plug in
> the remaining numbers to determine what the maximum SW for note 40 can be.
> KR and WW you have from your measurements.  Lets assume that WW is 18 and
> KR is .52.   It would look like this:
>
> SW = (40 + 30 - (.52 x 18))/5.5
>
> or
>
> SW = 11.02
>
> As you can see, a higher R will lower the allowable strike weight.
>
> That represents the maximum strike weight (without assist springs) that can
> be used without exceeding the FW maximums.  That number corresponds to zone
> 10 (1/4 high) in Stanwood's strike weight chart.  Subtract the shank strike
> weight from the strike weight (1.8 grams if a Renner shank is used) to
> determine what the hammer weight should be.  So on note 40, the maximum
> hammer weight that you can use without exceeding FW weight maximums for a
> BW of 40 in this system is 9.2 grams.  Use the zone in the published chart
> that corresponds and taper the hammers to achieve those weights.  Pretty
> easy.
>
> Now this is for the maximum front weight.  You may not wish to have the
> keys leaded to the max to keep inertia down in which case you can reduce
> your FW maximum to, say 80% of the front weight max.  Many old Steinway
> actions seem to come in around that number.  They also tend to have Rs that
> are around 6 or higher.  As you can see, with a higher R, a lower FW max
> and even a lower BW target, the maximum strike weight will be much lower.
> This is important to know if you are replacing hammers on an older
> Steinway, for example, without changing other parts or modifying leverage
> points.  It is also useful in determining why that newer Steinway needs so
> much lead.  Usually the problem lies in the KR.  A higher key ratio
> (capstan located too far back) will raise the overall ratio.  As an aside,
> also keep in mind that if you are modifying the KR, it is not enough to
> simply change the number to, say .50 and recalculate.  The new capstan
> position will change your measured UWs and DWs and the resultant R from you
> sample.   Should you decide that your overall ratio is too high (in the
> case of a total action rebuild) and wish to change it, then you will have
> to determine how a change in the knuckle position or capstan position will
> effect R.  Once you determine that, you can use the same methodology
> outlined above to determine your new hammer weights.
>
> David Love
> davidlovepianos@earthlink.net
>
>
>
>
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