Right Jon, The "standard" capstan-to-whip-heal-interface motion of the parts (beginning from rest) follows this pattern: 1) Slide with friction, 2) then roll at magic line with no friction, 3) and finishes with slide-friction. The indentation in a veteran whip cushion should reveal an oval shape. The involute slide path, supposedly described at the interface of a tipped capstan and sloping whip heal, should roll through the complete path, hence no friction (effectively). I have understood this to be the case for many years, but have never verified it for myself, although I have no reason to doubt Chris Robinson (I also took that class many years ago). The rolling condition obtains since the force line, or line of action, common to both the capstan and the heal runs along a tangent common to both surfaces. Said another way, "both contacting surfaces are always perpendicular to the plane of contact." Relative to gears, this condition exists as the gear teeth mesh; the teeth roll on each other without the immense friction and wear which would otherwise exist. Check out this link: <http://en.wikipedia.org/wiki/Involute_gear> http://en.wikipedia.org/wiki/Involute_gear -- has a neat animation. Nick Gravagne, RPT Piano Technicians Guild Member Society Manufacturing Engineers Voice Mail 928-476-4143 _____ From: pianotech-bounces at ptg.org [mailto:pianotech-bounces at ptg.org] On Behalf Of Jon Page Sent: Saturday, March 14, 2009 5:26 PM To: pianotech at ptg.org Subject: Re: [pianotech] key position at rest >Why they angled them backwards I'm still unsure of. The interaction between the angled capstan and angled cushion is called an involute gear (Chris Robinson stated this in a class many years ago). -- Regards, Jon Page -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://ptg.org/pipermail/pianotech_ptg.org/attachments/20090314/005ebe02/attachment.html>
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