<!doctype html public "-//W3C//DTD W3 HTML//EN"> <html><head><style type="text/css"></style><title>Center pin friction (was Re: Schaff spring)</title></head><body> <blockquote type="cite" 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 type="cite" cite> </blockquote> <blockquote type="cite" 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> </body> </html>