L/O Weight (was:Re: Kawai let-off (poor jack design?)

[Jon Page]

I would like to add a point (my view) in regards to L/O weight.

Repetition spring & jack spring tensions affect this.

Heavier hammers require a stronger rep spring so the resistence
will be increased during L/O. Conversely, a light hammer requires
lighter spring tension hence less resistence.

This brings to light  Dave Stanwood's desire to have the indivual
hammer's weight graduated. An erratic hammer weight for consecutive
keys will produce variations in spring tension.  By bringing the adjacent
hammer weight to .1gr (a smooth curve when plotted on a graph) spring
tension becomes more uniform and touch weight is more consistant (this
is just one component of Stanwood Touch Designs)  plug, plug, plug

Which is why the 'butterfly' type spring is superior to two separate
springs.  I would venture to say that on an action with separate
jack springs, the tension is_never_adjusted in the field for the jack.
However, with the butterfly type, the jack spring _is_adjusted
same-ol'-timeously with the repetition spring.

Aside from hammer weight and positioning the L/O button for minimal 
friction, the springs would control the degree of resistence during 
L/O which illustrates the need for minimal tension and uniformity.

That's how I see it.

Spring is in the air,

Jon Page

PS  What is this scale and where does one get it?
>a Kontaktor touch weight scale (25-250 gms for checking let-off weight) 

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At 05:37 PM 5/8/99 +1000, you wrote:
>Richard Moody and list,
>
>Richard wrote;
>
>>I have always been interested in the additional weight needed to push the
>>jack through let-off. You say it will require ADDITIONAL 150 grams.?? 
>>Perhaps you mean milligrams? Centegrams? 15 grams?? 
>
>
> When measuring down weight, up weight and let-off weight, it is 
>important observe the following;
>
>1) All measurements must be taken with the damper assembly lifted, ie. 
>with the sustain pedal depressed if checking in the piano, or with the 
>action on the bench.
>
>2) Ensure that the measuring instruments are accurately calibrated. I use 
>a Kontaktor touch weight scale (25-250 gms for checking let-off weight) 
>and gram weights from APSCO (for down and up weight). The APSCO gram 
>weights were originally quite inaccurate, for example, the heaviest 
>weight which was marked as 32 grams actually weighed 35. I spent 
>considerable time machining and grinding the weights to an accuracy of 
>better than 0.01 gram (I used my RCBS rifle powder reloading scale for 
>the calibration - [15.43 grains = 1 gram]).
>
>3) The down weight is that required to move the key slowly from its 
>resting position to the point where the jack tail just contacts the 
>let-off button. When the jack tail reaches the let-off button the 
>downward motion of the key will stop.
>
>4) When measuring the down weight, the gram weights should be placed 
>gently on the front of the key. Dropping them from a great height is 
>unlikely to give results which mean anything.
>
>5) The additional down weight is that required to execute let-off, and is 
>additional to the previously measured down weight.
>
>A procedure for measuring let-off weight
>
>Check the down weight of the key to be tested. With gram weights 
>equivalent to the measured down weight placed on the front of the key, it 
>will be depressed only to the position where the jack tail is in contact 
>with the let-off button. An accurate scale is used gradually to increase 
>the weight on the key until let-off is executed. For example, if a note 
>has a down weight of 50 grams, and an additional 125 grams is required to 
>execute the let-off, then the overall weight required will be 175 grams, 
>ie. the sum of the down weight of 50 grams and the additional let-off 
>weight of 125 grams.
>
>The let-off weight will vary from higher, in the bass, to lower in the 
>treble. The figures I quoted in a previous post referred to measurements 
>taken around note C40 (it is important to measure a couple of adjacent 
>notes to obtain averages, since there will be some note to note 
>variation). While key leads and/or wippen helper springs can be used to 
>control down weight with a heavier hammer, heavier hammers will increase 
>the loading between the roller and the jack. This results in a higher 
>let-off weight in the bass section, and vice versa for the treble section.
>
>It is important to remember that while the let-off weight is an indicator 
>of the relative after touche resistance for real world actions, we are 
>measuring this parameter under static conditions. When a piano is played 
>normally, the let-off resistance is barely noticed.
>
>Ron E. Overs
>Sydney, Australia
>
>Email: sec@overspianos.com.au
>Website: www.overspianos.com.au
>  

Jon Page,  Harwich Port,  Cape Cod,  Mass.  mailto:jpage@capecod.net
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