overcentering justified?

[Richard Brekne]

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Grin... Ok David P... you got me scratching my head here... How do you
come up with a stack raise of 2.8 mm to achieve 0 rake, 48 mm bore and
no overcentering based on the info Bob sent in ?...

Cheers
RicB

"David M. Porritt" wrote:

>  What would happen to the "magic line" etc. if you raised the stack a
> little?  2.8mm higher stack would get you 0 rake, 48mm bore with no
> over centering.  You'd have to check out all the other parameters --
> let off, etc. but I'd check that. dave
> *********** REPLY SEPARATOR ***********
>
> On 8/15/2003 at 3:57 PM Bob Hull wrote:
>
>      List,I have a question about appropriate bore distance to
>      see  if overcentering is justified, even designed into the
>      action from the first.  Here's the background for the
>      question(s):In determining the bore distance for a new set
>      of hammers on a Hamburg D, I have done the usual math to
>      determine a perfectly level shank when the hammer meets the
>      string.According to this the new hammers should be bored at
>      2" for the treble hammers which is a considerably longer
>      distance than the old hammers are bored at and also longer
>      than the specs I have from Steinway ( 48mm).The old hammers
>      overcenter due to their bore and even more so of course due
>      to their wear.  Was this intended by Hamburg in their
>      design?After boring at the longer distance I thought would
>      be better than their old short bore distance,  I see that of
>      course I have to lower the capstan to have a blow distance
>      like the old and of course the let off.  The result is that
>      1. The shank is only 1/8 or less of the cushion and 2. The
>      repetition speed is very mediocre.  (I can improve the
>      repetition speed on the long  bore distance hammer by
>      decreasing blow distance to about 1 5/8".)The old hammers
>      repeated very easily and as fast as you could want.  (The
>      old blow distance is about 1 3/4". I searched the archives
>      and read Ron Overs, Richard Davenport, Newton Hunt and Dave
>      Love about the benefits of a higher shank.  Also, Sam
>      Powell's article in the Sept. '93 Journal about the reduced
>      friction that comes from the knuckle not being too far below
>      the line. (Effects of Hammer Bore on Escapement Friction)
>      These seem to give some approval to overcentering.But, will
>      there be an unacceptable loss of power?  Won't the hammer be
>      sliding into the string rather than striking it at 90
>      degrees? If I resort to overcentering like the old hammers
>      on this piano, would it be advisable to hang them with a
>      positive rake angle to compensate?  Hamburg Steinway specs
>      call for 0 rake. I realize some of this may be a rehash of
>      an old subject, but any good guidelines would be
>      appreciated.Thanks, Bob Hull
>      -------------------------------------------------------------
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> _____________________________
> David M. Porritt
> dporritt@mail.smu.edu
> Meadows School of the Arts
> Southern Methodist University
> Dallas, TX 75275
> _____________________________
>
--
Richard Brekne
RPT, N.P.T.F.
UiB, Bergen, Norway
mailto:rbrekne@broadpark.no
http://home.broadpark.no/~rbrekne/ricmain.html
http://www.hf.uib.no/grieg/personer/cv_RB.html


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