<!doctype html public "-//W3C//DTD W3 HTML//EN"> <html><head><style type="text/css"></style><title>Re: Lever friction maths</title></head><body> <div>At 3:07 am +0200 23/6/07, Danilo Perusina wrote:</div> <div><br></div> <blockquote type="cite" cite>Hi! I posted this about twelve hours ago. Was it missed in the hurry, or deemed erraneous/ too incomplete? So many references since about how much increased friction actually affects the spring. I post it again then, and please ignore if the whole calculation is way out!:-)</blockquote> <div><br></div> <div>The designers of the Herz-Erard action were extremely exact in their calculations, so little is gained by bringing in such very approximate calculations as yours to prove that having a stiff centre provides more work for the spring to do and puts the spring under more stress than it is designed for to do a certain task, which is obvious.  Incidentally I think you will find that the standard bearing point of the spring is 25 mm. from the centre and not 30 mm.</div> <div><br></div> <div>In the 35 years that I have been restoring grand actions my experience has been that the centre of the repetition lever is the centre least likely to be affected my time and use and although I do re-centre the repetition lever on most jobs, it is rarely actually necessary, and this lever is almost always free enough to fall by its own weight and not to need the weight of a large coin at the end to make it fall.  Bill Garlick or no, I see no advantage at all in adding what is in effect a friction damper to a spring that was not designed to be damped and which can be adjusted to to its work effectively without such damping.</div> <div><br></div> <div>At 8:36 pm -0700 21/6/07, David Love wrote:<br> </div> <blockquote type="cite" cite>Pinning the rep lever tighter allows for speedier jack return as well as more positive hammer rise since the spring doesnÕt need to be set so close to the fail point.  Most of the benefit, in my view, comes from the speedier jack return and thus faster repetition.</blockquote> <div><br></div> <div>I don't see the logic of this.  No matter how much extra spring force is provided for the jack, the fly cannot return under the roller until the repetition lever has almost fully returned to its rest position, and this will occur no sooner with a heavy spring and a tight centre than with a lighter spring and a free centre.  Besides that, the jack needs very light spring pressure and will become increasingly noisy as the pressure is increased.  Many actions, especially American actions, provide a separate lighter spring for the jack in order that the heavy pressure required for the repetition lever in the bass shall not be applied also to the jack, which has no need of such pressure.</div> <div><br></div> <div align="center"><img src="cid:p06240806c2a28dea26c1@[10.0.0.1].1.0"></div> <div align="center"><br></div> <div>JD</div> <div><br></div> </body> </html>