[CAUT] Re: Leads, Magnets, Springs, etc.

[David C. Stanwood]

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