I took Chris Robinson's class a long time ago and not much is retained...I remember 2 intersecting circles which turned into gears. I remember his point was the careful engineering Steinway had built into their older pianos. The angled capstan...he made a point about the lack of wear on action parts because good engineering...someone needs to go to the horse's mouth...Chris. David Ilvedson, RPT Pacifica, CA 94044 ----- Original message ---------------------------------------- From: "Mike Spalding" <mike.spalding1 at verizon.net> To: pianotech at ptg.org Received: 3/15/2009 8:25:45 AM Subject: Re: [pianotech] capstain/wippen angle, was: key position at rest >This topic has interested / confounded me for years, and it's been >frustrating particularly because my engineering background, which >included a stint in the gear manufacturing industry, should allow me to >make sense of it. >First, thank you Nick for the link to Wikepedia. Look carefully at the >animation, and read the accompanying text. Notice that the reason for >using the involute in gears is not to eliminate sliding friction - >sliding friction and wear is listed as the main drawback of involute >gears, hence the need for effective lubrication on gears. The involute's >strength is that it transmits angular motion very smoothly. And it turns >out that, as you work with the pressure angle and other parameters to >optimize smoothness, tooth strength, and power ratings, you end up >increasing the amount of sliding. Also, note the definition of >"involute": "the spiraling curve traced by the end of an imaginary taut >string unwinding itself from that stationary circle". Does anybody >really believe that the top of the capstain, or the heel of the wippen, >are shaped like true involutes? But they do share one similarity with >involute gear teeth: They slide. >When Ron Overs unveiled his new action geometry in Reno, I was certain >he had discovered and corrected a major flaw in piano action design. >While standard parts don't allow us to go as far as Ron did, we could at >least convert angled capstain actions to vertical capstains. So why, >when I did just that (S&S L) did it make no improvement, possibly made >it worse?? >I like Dale's explanation: *The broad faced angled capstan actually has >an accelerating effect when positioned properly. At rest, the key side >edge of the Broad faced capstan touches on the wippen felt edge furthest >from the wippen center pin. As the capstan/wippen moves thru its >rotation the capstan moves upwards & rotates to the middle of the >capstan & then to the rear edge. SO, as it continues thru its arc, the >point at which the wippen is lifted moves to the rear edge of the >capstan & closer to the wippen pin thereby accelerating the key/action >motion. Kind of an automatic transmission affect.Things move faster >without shifting. >*If sliding friction is unimportant (especially if it's minimized by >polishing the cap and teflonning the wip heel), and if the change in >leverage during the stroke works as Dale describes, that would explain >my experience, and also the results of the "what happens if..?" >experiments. >Lots of good new information this morning, need time to digest it. >Mike >Nick Gravagne wrote: >> >> 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 -- 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 >>
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