[CAUT] Stringing equations and friction

[Ed Sutton]

If there are any bearing points, when raising pitch, the highest tension 
will be in the wire section closest to the tuning pin. Lubing the bearing 
points, including felts, might help.
Ed S.
----- Original Message ----- 
From: "Greg Graham" <grahampianos at yahoo.com>
To: <caut at ptg.org>
Sent: Saturday, December 05, 2009 9:44 PM
Subject: [CAUT] Stringing equations and friction


> I've always suspected the stringing equations were forgetting something, 
> namely friction at the bearing points.
>
> A year or so ago I wrote asking for advice on a piano with a C88 speaking 
> length of 63 mm.  The #13 Roslau wire I had wouldn't come up to pitch, 
> usually breaking at the capo.  I tried some #13 Mapes Int'l Gold and got 
> closer.  Mapes I.G. #12.5 got me to pitch after two tries, with gritted 
> teeth and squinty eyes.
>
> Here's the rub... literally:
>
> There is so much tension on that poorly scaled string that the capo 
> develops grooves as soon as you pull up to pitch.  There is LOTS of 
> friction going on.  A smaller wire, with less tension, will have less 
> friction.  That matters when you are talking about strings breaking, 
> doesn't it?
>
> Won't the segment of string between the capo and tuning pin always 
> experience higher tension and break percentage than the speaking length?
>
> If we reduce bearing point friction, won't we lower the difference in 
> tension between the two segments, thus allowing less breakage?
>
> I don't have the answers here.  I'm just the new guy (with a mechanical 
> engineering degree) looking for guidance and questioning authority.
>
> Greg Graham, RPT
> East Stroudsburg, PA
>