[CAUT] Fw: capo bar reshaping

[Paul T Williams]

Thanks mucho Alan,

This is the info I'm looking for.  The capo to front bearing angle was 
large enough to file down a bit of the front bars and now file "up" a bit 
of the capo.  Just 0.5mm total or so, just enough to get some of the 
grooves off the bar and front bars.  The angles I think, now, might be 
closer to "ideal".  I think maybe the best resolve is to average the two 
schools of thought and shoot for a 1mm radius with a bit larger (0.02mm in 
the lower parts and a bit narrower( or just at 1.0mm) in the high end. You 
reminded me of what Steve Brady taught me many years ago when I resurfaced 
a Bosey bar that was doing the same thing.  Thank you!!

Hardening a capo iron is something I know nothing about, so I may have to 
just see what happens..This is a practice piano, so,.....I'm practicing!! 
:>)

Thanks for your reply!

Paul




Alan McCoy <amccoy at mail.ewu.edu> 
Sent by: caut-bounces at ptg.org
09/10/2008 04:57 PM
Please respond to
College and University Technicians <caut at ptg.org>


To
"College and University Technicians <caut at ptg.org>" <caut at ptg.org>
cc

Subject
Re: [CAUT] Fw: capo bar reshaping






Hi Paul,

The email came through the first time. But the issue is a can o worms. The
proper shape of the capo depends on who you ask. If it is too pointy and 
not
hard enough, you quickly get grooves, which gives the capo a too flat
bearing surface. If it is too flat (as it is when grooves have been cut 
into
an otherwise sharp profile) then you will probably have noise (string
sizzle) at the capo. Also part of the puzzle is the angle between the 
string
plane and the duplex segment up to the counterbearing. If it is shallow it
won't cut grooves as quickly, but it may not terminate the string 
properly.
If it is steep, there is a tendency for cutting grooves. So what you need 
is
a decent counterbearing angle (anywhere from 12 deg to 20 deg though 
you'll
get arguments aplenty about what's the best angle) and you can get away 
with
a shallower angle if the counterbearing segment is shorter (long and 
shallow
will often give duplex noise especially if the length of that segment
happens to be harmonically related to the speaking length). Also you need
the capo to be properly hardened. And it needs to be profiled to some
radius. Talk to Ed McMorrow and he will advocate a very sharp (0.5mm 
radius,
I think). While others will advocate more like 1.5mm (about 1/16"). Me? I
use a Stewart MacDonald diamond fret file and file it to probably around 1
to 1.5mm radius. As a rebuilder (of sorts) and somewhat pragmatic I worry
less about the capo itself and more about the counterbearing angle and
length of duplex segment. That is really the only easily changeable part 
of
the equation. I know that some will harden the capo, but I don't have that
skill yet. But I do alter the front duplex when I think it will be some
benefit. Just finished grinding off the counterbearing bars of the piano 
in
my shop and will replace the bars with half-round brass. The angle won't
change much at all, but the segments will be significantly shorter (less
than 30mm my eyeballs tell me, though I haven't measured yet).

Like I said, can o worms.

Alan


-- Alan McCoy, RPT
Eastern Washington University
amccoy at mail.ewu.edu
509-359-4627
509-999-9512


> From: Paul T Williams <pwilliams4 at unlnotes.unl.edu>
> Reply-To: "College and University Technicians <caut at ptg.org>" 
<caut at ptg.org>
> Date: Wed, 10 Sep 2008 12:29:47 -0500
> To: <caut at ptg.org>
> Subject: [CAUT] Fw: capo bar reshaping
> 
> I'm not sure if this went through yesterday.  I'm trying again.
> ----- Forwarded by Paul T Williams/Music/UNL/UNEBR on 09/10/2008 12:28 
PM
> -----
> 
> Paul T Williams/Music/UNL/UNEBR
> 09/09/2008 01:23 PM
> 
> To
> caut at ptg.org
> cc
> 
> Subject
> capo bar reshaping
> 
> 
> 
> 
> 
> Hi List,
> 
> I'm working on a plate from a 1926 Steinway M that had been breaking 
lots
> of string along the capo.  Both sections broke about the same number of
> strings per semester.  Upon pulling the plate and looking carefully at
> both sections, the top section was really flat (plus grooved and crusty)
> and the lower section was more pointed like we like, but way deeper
> grooved (and just as crusty). So, my conclusion is that both too deep of
> string groove and too flat a capo surface experience the same amount of
> string breakage.
> 
> Now, I can't remember the width of the "peak" of the capo, but seem to
> think along the lines of 0.5mm-1.0mm (top to bottom of whole capo)
> 
>  Is this a bit too sharp? Could someone please remind me the proper
> "shape" before I begin filing?  Do all the string grooves need to be 
100%
> gone?
> 
> Thanks for the input!
> 
> Paul



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