<HTML> <HEAD> <TITLE>Re: [CAUT] about magnets</TITLE> </HEAD> <BODY> OK, let’s see ho= w much I can remember from “Elementary Strengths of Materials” f= rom 1976. Technically, springs don’t “wear out”.  The amount o= f force needed to bend or compress a spring a given amount, it’s &#822= 0;rate”, is dependent on what the spring is made of and it’s cro= ss-section area.  In the absence of corrosion, this doesn’t chang= e.  What does happen is that if a spring is subject to a constant stres= s, like a wippen spring that is slightly compressed when the key is at rest,= the shape of the spring will, over many years, conform to that stress. &nbs= p;I have also seen this happen with upright hammer springs – you unhit= ch the spring and it only moves a little bit, and it almost certainly didn&#= 8217;t start out that way.  Effectively, then, the spring isn’t c= ompressed as far as it once was in it’s rest position, so it’s n= ot exerting as much force.  The distinction, I guess, is pretty academi= c.  From the player’s point of view, the spring has worn out. Of course, corrosion is also a factor in old springs, usually in the form o= f rust, and it does decrease the spring’s rate by degrading the metal.=  And if you try to re-bend an old spring to regain it’s performa= nce very many times, you can weaken the metal some.  Like bending a coa= t hanger until it breaks. Synthetic magnets do slowly lose their field over time, at least theoretica= lly.  However, given the quality of magnets available today, I doubt th= at you could measure a change in the field after 100 years. That’s all I remember. Ken Z. On 3/22/05 4:41 PM, "Ed Sutton" <ed440@mindspring.com> wrot= e: <BLOCKQUOTE>O, Great Minds of Caut!   I have heard tell that Petrof is producing grand pianos with a magnetic ass= isted action, soon to arrive in our neighborhood.   The magnets are installed in the wippen rail and wippen in repelling orient= ation so that the magnets lift the wippen similar to a wippen assist spring.=  The touchweight can be refined by adjusting the magnets similar to a = screw regulated wipen assist spring.  Functionally it seems identical t= o a wippen assist spring.   When I asked how it differed from a wippen assist spring I was told "S= prings wear out, but magnets last forever."  I would be interested= in educated comments on that statement.  The magnets will be held cont= inuously in opposition and "compression."  Will they grow wea= ker over years? decades? or will they last forever?   How does this compare with assist springs?  Do wippen assist springs g= row weaker over time?  Faster than magnets?   Jim Ellis, I thank you in advance!   Sincerely, Ed Sutton   </BLOCKQUOTE> -- Ken Zahringer, RPT Piano Technician MU School of Music 297 Fine Arts 882-1202 cell 489-7529 </BODY> </HTML>