Dale, I think we'll have to go to Chris for the answer to that. The term "frictionless involute" doesn't ring any bells for me. An involute is a precisely defined geometric curve. A curve, in and of itself, has no friction properties. In my experience the capstain and wippen heel are neither involutes nor frictionless. I wish I had been there to hear the context of his remarks. Mike erwinspiano at aol.com wrote: > *Mike > I remember Chris R. using the term frictionless envolute. Does this > eliminate any problems ...or make things worse in the theoretical world? > Dale* > > > Mike S wrote > > 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, are20shaped 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=2 0it. > > 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> > [mailto: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 <mailto: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 > > > > > ------------------------------------------------------------------------ > Worried about job security? Check out the 5 safest jobs in a recession > <http://jobs.aol.com/gallery/growing-job-industries?ncid=emlweuscare00000001>. >
This PTG archive page provided courtesy of Moy Piano Service, LLC