[pianotech] WNG jack don't come back no more, no more, no more.....

["Rafael M. Huberman Muñiz"]

I have been following this discussion because I'm perplexed with  
reducing the tension in order to get the subject in question move  
faster/stronger.
I never encountered so far this problem but a similar one on some  
damper not damping in verticals. After changing damper felt and  
regulating the dampers some of them don't damp well enough so I  
usually increase the damper spring tension and most of the time that  
solves the problem, but every now and then I increase the tension and  
instead of damping better it becomes worst and I'm always intrigued  
with what's happening. Ron: are you saying that decreasing the spring  
tension will solve the problem?

Rafael Huberman


On 19/01/2012, at 03:14 p.m., Ron Nossaman wrote:

On 1/19/2012 8:03 AM, Dean May wrote:
> I'm having trouble understanding so I'm going to risk asking a stupid
> question. Could you or someone explain why the too heavy spring  
> could be the
> problem? I understood the complaint to be the jack would not slip  
> under the
> knuckle. Seems like too much rep spring tension would assist in  
> holding the
> rep lever high to make it easier for jack to return, not more  
> difficult.
>
> Thanks in advance.
>
> Dean

Sorry, been out bustin' inharmonicity.

Dean,
While there most certainly are such things as stupid questions, this  
isn't even close. We're talking about spring rate, which is specified  
as units of deflection per unit of weight, or how much a spring  
deflects under a given weight. So a high rate spring will will be  
stiffer than one with a low spring rate. In a repetition lever, we  
need a specific force over a broad range of spring travel. If the  
spring rate is too high, the force exceeds what we want as the spring  
is compressed, and we get the choice of too much spring force at the  
bottom limit of spring travel, or too little at the top. The power  
curve is too steep. A lower rate spring (lighter spring) will give a  
less steep power curve through the spring travel so we can get  
controllable and adjustable power throughout the stroke. Too low a  
spring rate may not give you adequate power at the bottom to get  
things moving, and will over stress the spring. So the spring rate  
should be chosen to accommodate the power requirements through the  
range of movement of the mechanism. This gives longest spring life,  
most dependable function, and easiest adjustment.

This is the extremely shortened version, but it's the gist of it. I  
can get more detailed if you need.
Ron N