Capstan Relocation

[Farrell]

Hi Richard. Thanks for your response and your interest.

----- Original Message -----
From: "Richard Brekne" <Richard.Brekne@grieg.uib.no>
To: <pianotech@ptg.org>
Sent: Saturday, October 14, 2000 1:40 PM
Subject: Re: Capstan Relocation


> > I am evaluating relocation of the capstan line on my Boston grand
because
> > the wippen heel cushion/capstan contact point lies well below the "magic
> > line" between the wippen center pin and the key bottom at the center
rail
> > pin. At full key depression, the contact point comes just up to the
magic
> > line.
> >
> Grin... just make sure you have correct hammer to string distance and
letoff and
> drop adjustments, proper key height and dip and correct spread BEFORE you
check
> contact point at the magic line. Assuming you have done this then ......

Yes, absolutely. Complete regulation of the note(s) is done after every
change.

> > I made a little adjustable capstan that I can slide back and forth along
the
> > key to search for the "sweet spot", as defined by Bob Hohf in his recent
PTG
> > Journal articles as the capstan location where downweight is least and
> > upweight is greatest.

I made a bad statement above. As you move the capstan toward the center rail
pin, Downweight AND Upweight decrease. It is friction that one is trying to
minimize. The lowest friction number is the "sweet spot". I'm not sure, but
I think that in "normal" cases friction may well continue to decrease as the
capstan moves toward the center rail pin because of overall increased action
efficiency, BUT an action is well designed enough, the wippen heel/capstan
contact point at half key depression will SOON rise above the magic line,
and thus friction (actually vector losses) will start to increase, resulting
in a "sweet spot". Playing around with my action, the friction seems to just
keep decreasing as I move the contact toward the center rail pin, but I
think that is because only after moving the darn capstan to the edge of the
heel cushion, has the contact point met the magic line at half key
depression.

> I also made a little temp capstan thingy... But it was the length of the
capstan
> and whippen cushion combined and could be "adjusted" by adding paper
punchings..
> I used this to go for ideal whippen travel for a given key height /
keydip.
> Havent tried Hohfs definition yet.. might be fun to compare the two.
>
> > Moving the capstan toward the center rail key pin will
> > increase action efficiency (Why does there seem to be no trade-off? Am I
> > missing something?). Lets say I move it 10 mm toward the center rail pin
(I
> > know, that's alot - just an example), up and downweight is more
favorable
> > and the contact point crossed the magic line at half its travel -
Perfect!
> > But, I could, for the sake of arguement, install a taller wippen heel,
lower
> > the capstan, and move it even further toward the center rail pin, thus
> > increasing action efficiency even more while keeping the heel/capstan
> > contact point right on the magic line at half key depression. What
limits me
> > from doing this?
>
> If you go in too far you will get... shall we say... to efficient. This
> efficiency is also connected directly to touchweight. You are changeing
> leverage.. move in too far and the touch will get like really really
light. You
> would have to have massive hammers to deal with it and there are optimums
with
> hammer mass as well as optimums elsewhere. Until we (you and I,,,grin)
know more
> I would suggest that you stick to getting as close to Stanwoods 9.0 grams
> combined key ratio and whippen radius weight figure, while at the same
time
> shooting for optimum whippen travel (ie jack just clears the knuckle at
letoff
> /drop). Keeping the contact point on the magic line as well. If you have
to
> change whippen cushions to do this then do so. (tho I would be suprised if
you
> had to in a Boston)

Yeah, that is certainly one thing that I keep in mind. I find it hard to
believe that Steinway would design grossly improperly dimensioned parts into
the action - poor assembly, yes - poor adjustment, yes - improper alignment,
yes - but a major action part way off, let's just say I would be a bit
suprised, but I will always keep my mind and eyes open! Sounds to me like I
should just shoot for a compromise that is not radically far from what I
currently have between the Stanwood key and wippen parameters, magic line
contact, proper whippen travel (that was always right-on), and Bob Hohf's
thoughts. OK, easy!

> > Key thickness? (I hope there is something else!) Common
> > sense (or what I perceive to be) certainly suggests that I leave good
enough
> > alone, but I want, er a, need, to understand the what and why. What?
Why?
> > Anyone?  ?-)
>
> We arent going to get a lot of response to this thread me thinks Terry.
Jon Page
> has been very helpfull to me, and probably the best help he has given me
is to
> kindly and patiently kick me in the butt to get my hands on experience
going.
> Tho I would welcome more discussion on this from others. I am really not
sure
> how many techs actively manipulate these parameters so much. Most techs I
know
> learn to regulate, but not how to set up regulation parameters.
>
> Have you tried sending copies of your queries directly to Bob Hohf ? I am
not
> sure he subscribes to the list..

Yeah. I just sent him two questions this morning. I always fear that someone
who has a piece published in the Journal gets lots of mail regarding it. I
hate to bug him. I'll see if he is able to respond. Will let you know.

> Keep us posted anyways. (me at least.. it helps me learn this stuff you
"hear"
> you think and ask questions

Same here. Really helps me to read this stuff and always try to understand
it.

> --
> Richard Brekne
> RPT, N.P.T.F.
> Bergen, Norway

 Terry Farrell
Piano Tuning & Service
Tampa, Florida
mfarrel2@tampabay.rr.com