In reply to David Stanwood: I'm not a chemist either, so I don't know the reason why some key leads corrode, while others don't. I suspect David might be right. Next time I see one of my chemist friends, I'll ask him. As for the repelling magnets at the back of the key compensating for attracting magnets at the front: That's only partially true. We are dealing with an inverse-square function here. If you plot force-vs-position, you get an s-shaped curve that is only linear in the middle - at the zero crossing. If the spacings don't change much throughout the stroke, the function is nearly linear for all practical purposes if the motion stays near the middle of the curve. As for springs, the same approach does not apply. Spring rate, for all practical purposes is linear, so the spring rate will get you, no matter whether it is compression of elongation. If the spring rate is not too great, it will be fine for all practical purposes. In the case of wippen-assist springs, the spring rate and angular motion are such that there is little change in the force that is felt at the front of the key. However, if you were to use a very stiff wippen-assist spring, and regulate it so that it would only exert the required force in the key-up (wippen down) position, it would disengage before the key bottomed out, and I guarantee you that an experienced pianist would feel something strange with the touch. There is a trick you can do with a spring that will partially compensate for the spring rate, and that is to put it on an angle with respect to the motion, but the geometry gets messy, and for the sake of this discussion, I don't want to go there right now. Sincerely, Jim Ellis At 12:00 PM 3/30/05 -0700, caut-request@ptg.org wrote: >Send caut mailing list submissions to > caut@ptg.org > >To subscribe or unsubscribe via the World Wide Web, visit > https://www.moypiano.com/resources/#archives >or, via email, send a message with subject or body 'help' to > caut-request@ptg.org > >You can reach the person managing the list at > caut-owner@ptg.org > >When replying, please edit your Subject line so it is more specific >than "Re: Contents of caut digest..." >Today's Topics: > > 1. Re: Leads, Magnets, Springs, etc. (David C. Stanwood) >Date: Wed, 30 Mar 2005 12:29:37 -0500 >From: "David C. Stanwood" <stanwood@tiac.net> >To: caut@ptg.org >Subject: [CAUT] Re: Leads, Magnets, Springs, etc. >Message-ID: <6.1.2.0.2.20050330120601.026d8de0@pop.tiac.net> >Content-Type: text/plain; charset="us-ascii"; format=flowed >MIME-Version: 1.0 >Precedence: list >Message: 1 > >Hi Jim et al, > >A few comments on Jim's comments..... > >>Lead weights in piano keys can sometimes be a problem. I have seen leads >>in keys 100 years old where there was little if any corrosion. I have seen >>others half that age where there was very bad corrosion, swelled up leads, >>binding keys, and lots of lead oxide dust in the key bed. That stuff is >>very toxic - really bad stuff. I can see why the Germans might want to ban >>lead in piano keys. That stuff is extremely toxic, and once you get it in >>your system, your body has no good way of getting rid of it. It causes >>brain damage big time. The only thing worse is mercury, but fortunately, >>we don't use mercury in pianos. > >I think that the 99.99% pure lead doesn't corrode (as seen in those 100 >year old pianos..) I think that when the lead is impure there are things >that happen which cause chemical reaction.. These might be electrolytic in >nature and therefor more of a problem in humid climes, but I can't say for >sure as I'm not a chemist.... There are a lot of lead weights on the >market that are impure with other metals in them... Usually these leads >leads are harder to swage than the 99.99% pure stuff... > >>Weights have something going for them that springs and magnets do not. A >>weight will exert the same force on the key, whether it is up, or down. A >>magnet or spring will not. With a magnet, you will have the inverse square >>law that causes the force to decrease as the magnets get farther apart. >>With a spring, you have the spring rate that varies linearly (according to >>Hooke's law) as the spring is compressed or exteded, as the case may be. >>If the spring rate is too much - the spring too stiff - you will feel this >>effect on the key. If not, you won't. The same idea carries over to the >>repelling magnets, but for a different reason. > >The trick of the magnetic balancing is coupled magnets for and aft of the >balance rail.... when the key moves down and the attracting mags in the >front attract more strongly as the gap decreases... at the same time the >repelling mags in back repel less as the gap widens... So this compensates >for aforementioned effect... I've done several studies of this with keys >tipped on the scale and with the right combination of magnets and gaps >there is little or no significant difference between the total mag force at >the front of the key at the top of the stroke compared to the bottom... >I've done the same studies with springs and there is little or no >significant difference between the top and bottom of the stroke... You can >see also that the motion of up weight and down weight is normal with >springs or mags on or off..... so these kind of effects are negligible as >far as I can see... > >Hope this helps, > >David Stanwood > >_______________________________________________ >caut list info: https://www.moypiano.com/resources/#archives >
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