[CAUT] Re: Moving Capstans

[Alan McCoy]

> This message is in MIME format. Since your mail reader does not understand
this format, some or all of this message may not be legible.

---------------------- multipart/alternative attachment



> From: Jon Page <jonpage@comcast.net>
> Date: Tue, 26 Oct 2004 12:24:58 -0400
> To: <amccoy@mail.ewu.edu>
> Subject: [CAUT] Re: Moving Capstans
>=20
> Alan,
> With the capstan in its present location, where does the jack end up at t=
he
> bottom of the keystroke?

Good question. The jack is in good position =AD midway between the knuckle an=
d
window felt.
>=20
> If it is buried into the stop felt there is latitude to move the capstan
> forwards while keeping the dip at
> 10mm (hopefully where it is now).
Dip is at about 11mm. Blow about 1 7/8=B2, and some aftertouch.

You want the jack to be just in front of
> the knuckle at full dip.
> Hammer bore is important too, so don't go moving capstans with worn hamme=
rs.

Brand new hammers.
>=20
> With the hammer/key set at half blow *, draw a line perpendicular to the
> heel through the contact point
> (hopefully it's on the Magic Line) and extend onto the key. This is an
> optimal capstan angle.  If the heel is
> straight 'perpendicular' is a line which is parallel to the rep support
> post.  Many a time, just by reducing the
> acute angle gets the action to regulate properly.
>=20
> Prop up a tri-square with a spring clamp, set the half-blow height on the
> square, put a weight on the key. This I can=B9t quite visualize.
>=20
> Regards,
>=20
> Jon Page
>=20
> PS  4.38" is perfect for action spread.
>=20
> If this is a B, I'd bet that the balance rail is too far forwards (or an
> M). =20

It is a 7=B9 Chickering.

Your best bet may be to install a balance rail shim.
> I did it last month on a B, it was the only thing that would work. It
> changed the KR from .56 to .52, reducing friction and
> touchweight.

I was called in to evaluate this piano, and noticed as I was tuning that it
played like a Peterbilt. Week later brought my Stanwood stuff. Took
measurements. Began doing =B3what ifs=B2 in my spreadsheet. All the numbers
pointed to moving the knuckle (kind of a no-brainer to move from 16mm to
17mm, right?) and also to moving the capstan closer to the balance rail.
Moving the capstan this way brings the action closer to convergence,
improves key ratio & WBW, brings down BW and R all of which this action
needs, right? Hence my original =B3what if=B2 question about how to predict the
effect on BW that moving a capstan or knuckle has. The analysis is very
circular.=20

So here is the scenario:
What if I move the capstan to achieve a KR of .50? Plug that into the sheet
and I have the new WBW.
I know that BW will go down and so will R. But how much?? If I could plug i=
n
an estimate for how much DW and UW would change , then voila, the sheet
calculates R . Then I can play around with SW and FW and plug those back in
to figure out the parameters that this action will allow. Very circular.

Thanks a lot for your thoughts.

Alan




>=20
>=20


---------------------- multipart/alternative attachment
An HTML attachment was scrubbed...
URL: https://www.moypiano.com/ptg/caut.php/attachments/10/3a/e4/b1/attachment.htm

---------------------- multipart/alternative attachment--