Hammer assist spring ?

[David C. Stanwood]

>This progressively reducing assist force is one of the disadvantages 
>of assist springs. The wippen, by virtue of it small degree of 
>rotation, is the more practical of the two levers to assist. We have 
>reduced the lack of linearity by including an extra coil in the 
>spring. And yes I agree with you Bill (Ballard), when there is no 
>adjustment screw, setting the assist spring pressure is nothing short 
>of a pain.
>
>Ron O.

Hi Ron,

I have never considered it to be a problem because the motion of the hammer
when measuring up and down weight without springs is not significantly
different with them.  You roused my curiosity..... (Thank You!) so I just
did this little experiment:

I set up a key on the digital scale to measure Front Weight.  I attached a
rail to the metrology table and hung a wippen, (with very low friction in
the flange), on the rail so that it sits nicely on the capstan.   I loaded
jiffy leads on the wippen to simulate the force of the hammer-shank-knuckle
that would normally sit on the wippen.  I then held the front of the key
down on the scale by loading the front of the key with a 100 gram weight.
Then I tared the scale to zero and hooked up the spring.  The scale reading
indicated the spring was working 17 grams, a figure considered by many,
including myself, to be a safe maximum for the amount that a wippen spring
should be designed to reduce the touch weight by.   Then I lowered the
scale by 10.5mm simulating a maximum keydip.  The reading changed by 1.5
grams.  When the spring was working 12 grams the reading was closer to
gram.  So it looks, according to this sample, like about an 8% reduction in
the working effect of the spring at the front of the key from top of stroke
to bottom...

Hmmmm... Interesting.....

Regards,

David Stanwood