<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN"> <HTML><HEAD><TITLE>Center pin friction (was Re: Schaff spring)</TITLE> <META http-equiv=Content-Type content="text/html; = charset=iso-8859-1"> <STYLE type=text/css>BLOCKQUOTE { PADDING-BOTTOM: 0px; PADDING-TOP: 0px } DL { PADDING-BOTTOM: 0px; PADDING-TOP: 0px } UL { PADDING-BOTTOM: 0px; PADDING-TOP: 0px } OL { PADDING-BOTTOM: 0px; PADDING-TOP: 0px } LI { PADDING-BOTTOM: 0px; PADDING-TOP: 0px } </STYLE> <META content="MSHTML 6.00.2800.1400" name=GENERATOR></HEAD> <BODY bgColor=#ffffff> <DIV><STRONG>torque</STRONG><SUP><FONT size=-1>1</FONT></SUP> =   <A href="https://secure.reference.com/premium/login.html?rd=2&u=ht= tp%3A%2F%2Fdictionary.reference.com%2Fsearch%3Fq%3Dtorque"><IMG alt='Audio pronunciation of "torque"' src="http://cache.lexico.com/dictionary/graphics/AHD4/JPG/pron.jpg" border=0></A> <SPAN style="DISPLAY: none">(</SPAN><SPAN style="BORDER-RIGHT: 1px solid; BORDER-TOP: 1px solid; FONT-SIZE: 7pt; = BORDER-LEFT: 1px solid; COLOR: red; BORDER-BOTTOM: 1px solid; = FONT-FAMILY: verdana, sans-serif; BACKGROUND-COLOR: = #ffffcc"> P </SPAN><SPAN style="DISPLAY: none">)</SPAN>  <A class=linksrc title="Click for guide to symbols." onclick="ahdpop();return false;" = href="http://dictionary.reference.com/help/ahd4/pronkey.html"><B><FONT = color=#0033ff>Pronunciation = Key</FONT></B></A>  (tôrk)<BR><I>n.</I> </DIV> <OL> <LI>The moment of a force; the measure of a force's tendency to = produce torsion and rotation about an axis, equal to the vector product of the = radius vector from the axis of rotation to the point of application of the = force and the force vector. <LI>A turning or twisting force.</LI></OL> <DIV>Terry Farrell</DIV> <BLOCKQUOTE dir=ltr style="PADDING-RIGHT: 0px; PADDING-LEFT: 5px; MARGIN-LEFT: 5px; = BORDER-LEFT: #000000 2px solid; MARGIN-RIGHT: 0px"> <DIV style="FONT: 10pt arial">----- Original Message ----- </DIV> <DIV style="BACKGROUND: #e4e4e4; FONT: 10pt arial; font-color: = black"><B>From:</B> <A title=fordpiano@earthlink.net = href="mailto:fordpiano@earthlink.net">Phillip Ford</A> </DIV> <DIV style="FONT: 10pt arial"><B>To:</B> <A = title=pianotech@ptg.org href="mailto:pianotech@ptg.org">Pianotech</A> </DIV> <DIV style="FONT: 10pt arial"><B>Sent:</B> Saturday, December 18, = 2004 11:15 AM</DIV> <DIV style="FONT: 10pt arial"><B>Subject:</B> Center pin friction = (was Re: Schaff spring)</DIV> <DIV><BR></DIV> <BLOCKQUOTE cite="" type="cite"><FONT face=Arial>Now I haven't = tried this, so I may well be speaking out of ignorance, but I have a reasonable = concept of how much flange friction there will be with 3-4 grams of = resistance. A jack weighs almost nothing. Seems to me if the jack needs to swing = freely 7 full swing cycles, that would require almost no friction in the = center. Three to five grams friction in an action center with a shank and = hammer hanging from it will swing maybe three full cycles - and that has = tons more momentum. Seems like something may not be right = here???</FONT></BLOCKQUOTE> <BLOCKQUOTE cite="" type="cite"> </BLOCKQUOTE> <BLOCKQUOTE cite="" type="cite"><FONT face=Arial>Terry Farrell</FONT></BLOCKQUOTE> <DIV><BR></DIV> <DIV>I think there a couple of things askew here.  One is that = some people are talking about hammer flange center pins and others are = talking about jack center pins.  Two is that, with regard to center pin = friction, a gram reading by itself is meaningless.  Action centers rotate, = and that rotation is caused by a torque, not a force.  And the friction = associated with them is measured by a torque, not a force.  A gram reading = is a measure of force.  To get a torque you have to know the distance = from the center that the force is applied.  On a hammer flange, 4 grams = applied next to the screw hole gives a completely different torque than 4 = grams applied at the tip of the flange.  If you're going to specify a = gram reading for flange friction then you also need to define the point at = which you're taking that gram reading.</DIV> <DIV><BR></DIV> <DIV>Phil Ford</DIV> <DIV>San Francisco, CA, USA, Earth</DIV></BLOCKQUOTE></BODY></HTML>