You can minimize this effect by using a weaker spring and winding it up more. A spring that generates less force per distance change will have less total percent distance change for a given movement. For example if you have a spring that generate 15 grams when compressed 90 degrees, there is an approximate spring equation that says force = K * degrees. K in this case would be 15/90 = .1666. A 10 degree change results in a change of 10 * .1666 = 1.666 grams. A weaker spring with twice as many windings will require 180 degress compression to get the same force. This gives K = 15/180 = .0833. For this spring a 10 degree change results in only a .833 g change in force. So you can have the same force but less change in force and less of a "springy" effect by using more windings (or smaller gauge wire). Of course there's only so much space for that little spring. -Mark ----- Original Message ----- From: "David C. Stanwood" <stanwood@tiac.net> To: <pianotech@ptg.org> Sent: Saturday, June 07, 2003 4:19 PM Subject: Re: Hammer assist spring ? > >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 > > > > > > > > > _______________________________________________ > pianotech list info: https://www.moypiano.com/resources/#archives
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