And then, I've heard the S&S C&A techs just say shoeshine it with emory cloth. You're right. Huge can o worms. No. This isn't intended to rebut your recommendations or provoke controversy. Just pointing out how far apart the differences are. Jeff ----- Original Message ----- From: "Alan McCoy" <amccoy at mail.ewu.edu> To: <caut at ptg.org> Sent: Wednesday, September 10, 2008 5:53 PM 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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