<html> <head> <meta http-equiv="content-type" content="text/html; charset=ISO-8859-1"> </head> <body bgcolor="#FFFFFF" text="#000000"> <pre>Ron said: It's not an intersecting arcs thing, it's a spring deflection and friction thing. The 72° back check face angle provides the wedge, sprung by the back check wire, to jam the tail to a stop. The tail radius splits the difference between too shallow an angle (large radius) that will grab but the height at which it ends up is very dependent on the force of the blow.</pre> <pre class="moz-signature" cols="72"> So that sounds like the specifications are empirical not something you can easily predict on paper. So that brings up the second question: The 72deg check face (how'd you do that degree sign), 2-1/2"-3" rad tail, back check head height 1mm below tail at letoff, 1" min tail...are these specs that work on "standard" 17"-19" length keys only (call it 8-1/2"-9-1/2" back lever)? What about a shorter back lever, with its smaller radius at the backcheck? ALthough "D's" go the other way and have longer key lengths than 17-19, so maybe that shouldn't change things that much? Jim Ialeggio -- Jim Ialeggio <a class="moz-txt-link-abbreviated" href="mailto:jim@grandpianosolutions.com">jim@grandpianosolutions.com</a> (978) 425-9026 Shirley, MA</pre> </body> </html>