From Tony Caught, Wednesday, June 29, 2011 2:39 AM > How do you harden the capo bar in a grand piano. > > Have a Yamaha CF that is buzzing wildly in the upper treble. I am going to release the tension on the strings in the upper section then seesaw some emery paper over the grooves to get the bar smooth but this bar is IMO to soft. Can this be chemically treated to harden it or how should it be done. > > > > Tony > Hi Tony, I have never hardened a capo bar, but the case hardening via of metal is a fairly well-understood phenomenon. The Wikipedia page (case hardening) has some info to get you started. I saved the following long Pianotech thread from Ron Overs and several others a few years ago. I think it might be of some use to you. My apologies for the length of this email, but I thought that the whole thread should be preserved, and I didn't want to pre-decide which parts you might find to be the most useful. Joe DeFazio Pittsburgh > >> From: Ron Overs <sec at overspianos.com.au> > > Date: March 4, 2009 4:07:40 PM EST > To: pianotech at ptg.org > Subject: Re: [pianotech] Capo Bars > Reply-To: pianotech at ptg.org > > > David, > > Why do manufacturers harden capo bars rather than cast (or grind) the underside of the strut flat, rout out a groove to receive a steel rod of proper radius, shape and hardness and insert it there where it could, when it's worn, be easily changed and where the consistency would be more easily controlled. Is there a compelling reason not to do it that way? > > Yes, this is a way to build a capo' with a controlled profile and a hardened surface. When the first Yamaha grands came out in the late 70's with the V-pro plates, they used a bar under the capo just as you've described. I seem to remember from their literature at the time that they mentioned a hardness of C60 for the bar. Piano wire is typically about C45, and a mild steel nail would be around C20. > > I have also experimented with the inserted bar, finding that it is critically important that the bar is seated well all along its length. If there are any sections where the bar is not being supported by the cast iron groove the tone will be weak and short at that point. > > The other question of course is how many manufacturers are actually hardening bars. Of the two that I know of, Yamaha and Steinway, neither of them are hardening the front duplex bars. One of the reasons why I suspect that Yamaha stopped using the inserted bar was that with the combination of string approach angle, bar radius and hardness they were using, there were quite a few string breakages. I have found that string breakages are definitely more common when the bar is hardened, if the piano is being regularly serviced by a technician who drags the strings all over the shop during tuning. If the tuning is carried out with minimal string movement once the piano has fully settled down, I have found that the string longevity on pianos with hardened bars is very good. > > I've just published a page on my website, which is actually a "more-information" page for the Australian market, and supplementary to a small advertisement we are running in Limelight magazine (a link to the page is included in the ad'). The page is mostly a promo' for rebuilding during the economic down turn, but you can see the front duplex images down the page in the 'Photogallery' section. There is some explanatory text under each image. > > http://overspianos.com.au/more_info.htm > > On the page I have images of a D which we rebuilt recently, with an image of a new Hamburg Steinway immediately below it. Both images show a close-up of the front duplex bars. Steinway don't harden their front duplex bars, and I suspect that this is why they use such a flat top surface. We shape the front duplex bars down to the same radius as we use for the capo, and harden them also. For some pianos, when the customer is prepared to pay the cost, we grind off the front bars completely and make new front duplex bars. This allows us to relocate the bars closer to the capo, to reduce noise, and to set the front duplex distance to a de-tuned length, with respect to the speaking length of each note. This helps to further reduce string noise. But I believe that the biggest factor in counter-bearing noise is length. Make them shorter and noise reduces. > > At this time David, we have settled on hardening the original capo bar after profiling, ie. we don't use the inserted rod idea. This is not without its problems. The most usual is that many manufacturers repair flaws (blow holes and such) in their capo bars by drilling and fitting a plug (which is probably made from mild steel) into the bar. This is very common in Steinway pianos, which unfortunately is the piano which we rebuild more than any other brand. The plugs will not harden because their carbon content is too low. We have been grinding them down with a die grinder and welding the hole with cast iron. This is a difficult process and we often have to repeat a repair, since it is common to have the repaired fillet crack post hardening. The other problem with hardening is that a lot of paint and filler gets burned off the bar during the hardening. Over the years we have gotten better at this, so we burn a lot less of the paint than during our first year of hardening (1995). > > Hardening still is a big job if it is taken on as part of the rebuilding process. I still believe it is worth it, because the tone in service sounds like a new piano for longer. I also believe that it is worth hardening the front bars. For domestic clients who typically have their piano tuned only annually we reshape the front bar but leave it unhardened. But for commercial clients I regard hardening the front bar as essential. > > Secondly, if I were to do that to a piano where I have some concerns about the hardness and or consistency of the capo, what specific material and diameter would be best to use for the rod insert? > > My experience is that the inserted rod option is more trouble to fit compared to the work involved in shaping and hardening. So we continue to reshape and harden. If you harden an S&S bar today you'll now be rebuilding to S&S standard, which clearly is not strictly their own standard, it is something which they took from somebody else. > > I can't comment on recent US Steinway D bars since I've only rebuilt one 1925 piano, and that was back around 1990, when we were reshaping but not hardening (we see very few US made S&S in Australia). All our other S&S rebuilds have been Hamburg instruments. Our first D, in which we hardened the bars, was for Queensland Conservatorium. Steinway wrote a damning report, criticising us for hardening the bar, saying that we 'knew nothing about tone-building the Steinway piano' (I have a copy of the report, which was kindly and anonymously faxed to me by an unknown supporter). They claimed that we had ruined the piano and that it would have to be sent back to Hamburg to have a new plate fitted. This banter went on for six months, during which time I got very little paid work done. After months of shouting down the phone, the problem subsided. Eventually, the institution was talked into a new D. The 'modified' instrument ended up in the hands of a dealer, who was a known slick operator but he also was quite a piano player. I heard reports that he claimed it was one of the nicest Ds he had played - not that it means much, but it felt like a little compensation for the effort and trouble we had been through. > > I don't know when Steinway actually started hardening their bars (if anyone has this information I'd like to know), but it certainly was happening by 2000, since we've rebuilt a 2000 D which had hardened capo bars. On this particular instrument the hardening had shelled off at the lowest end of the capo, so we had to re-profile the bar and harden it again, but I'd say that most of the time with these pianos it should be possible to simply fit new wire, although the front duplex bars are soft and of a large radius, and I do believe that the front bars are a source of noise also. We've found that the pianos are a bit cleaner, even if we just reshape and harden them, without fitting a new re-positioned front bar. > > Since S&S are now having all their plates for both Hamburg and NY made at their Kelly foundry, it would be interesting to know if they are hardening the capo's for the US pianos. If any of you have a late US D in your care, check out the capo bar surface with an inspection mirror. If you can see string grooves where the strings have been moved, they are not hardened. If the strings can be moved easily without marking the bar they are hard. I'd be interested to know. It is quite possible that the US bars are not being hardened, because the Hamburg plates are being hardened in Hamburg after the plates arrive from the US (I've got a photo of the machine they use for the process - which a visitor to the plant, at a certain time, sent to me via email from somewhere which shall remain un-named). > > Sorry for the length of this post. I'd better go to work. I'm currently getting covered in compound buffing another model O rebuild, which is a bit of a yawn since the client wasn't prepared to fork out the funds for the cost of a tenor bridge (the economic downturn killed off the tenor). But I've done the maths for this model now. It looks like a very suitable model for an upgrade. > > Ron O. > -- > OVERS PIANOS - SYDNEY > Grand Piano Manufacturers > _______________________ > > Web http://overspianos.com.au > mailto:ron at overspianos.com.au > _______________________ > --- > > From: Ron Overs <sec at overspianos.com.au> > Date: March 5, 2009 3:57:27 PM EST > To: pianotech at ptg.org > Subject: Re: [pianotech] Capo Bars > Reply-To: pianotech at ptg.org > > > But if brass is softer than the steel music wire, and I presume softer than unhardened cast iron, then isn't the steel wire going to cut a groove into the brass capo insert? And isn't that what we're trying to avoid? > Terry Farrell > > > > Terry and all, > Indeed, that's exactly what happens, and yes it is what we are trying to avoid. There will be considerable variations in the drawing and treatment of various alloys, which is bound to result in considerable hardness variations. Some may be harder than unhardened cast, but I don't believe any are really suitable for supporting piano wire, because they are relatively too soft. I'm not a big fan of using other alloys for the capo, and I have replaced them a couple of times with hardened silver steel (which in its cheapest form is a straight high carbon alloy, and its not necessary to use the more expensive oil-hardening grade) with much improved results. > > I can say from experience that the modern capo, if not hardened, is a disaster on account of its softness. As I have written previously, I suspect that this phenomenon of so much noise may be in part due to the longer freeze times which result from modern foundry practice - where two-pack chemical binders are typically used for the moulding sand and the mould is drier before the castings are poured. Overly long front counter-bearing lengths are as much to do with the problem. Our colleague Ron N. has also written about this in this thread. > > Despite the fact that cast iron doesn't have as favourable a friction coefficient as some of the other alloys, when bearing against piano wire, the grooving that occurs with other alloys makes them also drag during rendering. While unhardened cast iron is not very good either, when properly hardened (there is hardening and hardening), the strings will render at five years just like the day that the piano was strung. I know this because I've been doing it for enough years, and following up our own instruments on a regular basis to know that it is a fact. The tone will still 'age' when the bar is hardened because tonal deterioration is a result of both bar and wire deformation, but the deterioration is less when an appropriately radiused and hardened bar, with appropriate string approach angles are used. > > As I've written previously, care has to be applied with regard to maximum string approach angle and not making the bars too small in radius (which I have to avoid a propensity to do, in search of that really clean tone), but provided a commonsense approach is used, I believe hardening is a worthwhile practice for quality tone building. > > Yesterday one commentator said > > > Why do manufacturers harden capo bars... > > Do they? How? Cast iron is hard anyway. > > Modern cast plates are very soft unless they are hardened. For any who doubt my claim, try placing a piece of piano wire across the capo bar at the strut between the two top string sections and hitting the wire towards the capo with a small hammer. The bar will be mangled while the wire will be untouched. If the same test is carried out with a hardened bar, the bar will be untouched while the wire will be mangled. > > The hardness of the cast iron is related to both its analysis and the freeze time. Longer freeze-time plates such as V-pro plates, are very soft. They also don't respond to hardening as well as conventional sand cast plates. I seem to remember that V-pro plates typically have a higher phosphorus content to make them pour better. If this is so it may be the reason why they don't harden as well since phosphorus is known to reduce the effect of flame hardening. If there are any foundry men out there, they might like to comment on this. > > I also did a custom job on a capo for a dealer here in Sydney in late 2006. The piano had a plate with a soft capo bar and a short counterbearing length. There were problems with the tone of this quite new piano despite the fact that the counterbearing length was short, and I recommended that we shape and harden the bar. When I attempted to harden the bar it wouldn't cooperate at all. So I ground off the capo V, manufactured a new bar, hardened it and fitted it. The result was most satisfactory. Here's an image of the bar shown ready to be fitted to the piano. It is hardened and polished but not plated. > > > If you can't see the image, a copy can be found at; > > http://users.tpg.com.au/ronovers/ptr.custom.capo.jpg > > The square-section bar in the image is the off-cut of the ground stock from which the new bar was made. > > There seem to be some who doubt whether a clean tone can be had from a piano with hard bars. Below are links to full length tracks of an Overs 225 with hardened capo's and hardened and detuned front duplex bars. These mp3 files were converted from an audio CD at 192K, so the sound is good with a freshly restarted computer using headphones or decent speakers. > > http://users.tpg.com.au/onyxer/Corelli.mp3 > Scott Davie's recording of Rachmaninoff'sVariations on a Theme of Corelli, Op. 42 > Piano: Overs 225 no. 3 - duration 18'38 > > Sydney jazz pianist and composer Mike Nock recorded a CD with his trio on an Overs 225 piano. The following mp3 of Mike's composition,Acceptance, can be heard at; > > http://users.tpg.com.au/dotmewes/Acceptance.mp3 > Piano: Overs 225 no. 3 - duration 7'04 > The performers are; Mike Nock - piano, Brett Hirst - acoustic bass, Toby Hall - drums. > > > Ron O. > --- > From: Ron Overs <sec at overspianos.com.au> > Date: March 5, 2009 4:16:09 PM EST > To: pianotech at ptg.org > Subject: Re: [pianotech] Capo Bars > Reply-To: pianotech at ptg.org > > > No, my question is why the heck do they make agraffes out of brass? Maybe even more noise with an all steel agraffe? > > Terry Farrell > > Terry, > > The best set of agraffes I ever used was a custom set I made for a very-high-use Steinway D. I made them from SAE 1040 carbon steel, which was EN plated in the usual way that we have been doing it. The harder 1040 is much better than brass, since it provides a stronger substrate which is less prone to collapse. I built them in 1998. The piano is still in service and the agraffes are still clean. > > Why don't I build them for all of the pianos we do? It took me a week to build the test set on the lathe with my milling attachment. I understand the Steinway rep here (who is also a technician) criticised the parts because they weren't factory standard - amazing stuff. This is how pianos have been stuck-in-a-rut for a 100 years. The factory that dominates the others doesn't give a damn about the craft, just the politics. So nothing changes. > > Ron O. > -- > OVERS PIANOS - SYDNEY > Grand Piano Manufacturers > _______________________ > > Web http://overspianos.com.au > mailto:ron at overspianos.com.au > _______________________ > > --- > > > > From: John Delacour <JD at Pianomaker.co.uk> > Date: March 5, 2009 4:38:18 PM EST > To: pianotech at ptg.org > Subject: Re: [pianotech] Capo Bars > Reply-To: pianotech at ptg.org > > > At 11:06 -0500 5/3/09, PAULREVENKOJONES at aol.com wrote: > > There is a mythology here that begs correction. Brass is not "self-lubricating". There is no "lubricity" to it at all. There is a significantly lower friction coefficient between brass and steel than between cast iron and steel particularly because of the different galling characteristics of them. > > It depends what you mean by "significant". So far as I can see, the coefficients of friction hard steel/brass and hard steel/cast iron are not very far apart. The coefficient for steel/steel is far higher than either. For copper-lead alloy or leaded bronze the coefficient is really significantly lower. > > But it is no use going simply by the figures in engineers' handbooks. The slightest amount of lubrication will greatly alter the friction coefficient, and the behaviour of each pair of metals needs to be measured under lab conditions to arrive at any useful figures. Besides, there is not one single composition for the "brass" alloy. > > One thing seems to be certain, and that is that steel, and especially hardened steel, is a bad option unless it is lubricated. Brass or cast iron unlubricated have behaved to most people's satisfaction since the 1850s, with cast iron, in practice, being better, since there is not a sudden change from static to sliding friction. > > For a capo bar I would prefer solid bronze containing the optimum lead content. I'm no great lover of Bösendorfers but in this regard I like their choice. > > JD > > Some useful general information and tables can bee seen here: > <http://www.roymech.co.uk/Useful_Tables/Tribology/co_of_frict.htm> > > > > > --- > From: <pianoguru at cox.net> > Date: March 4, 2009 5:35:26 PM EST > To: pianotech at ptg.org > Subject: Re: [pianotech] Capo Bars > Reply-To: pianotech at ptg.org > > > As others have said, very few manufacturers harden the capo bar. None of the manufacturers for whom I have worked have done so. My only experience with hard terminations were the Baldwin SD-10 and SF-10. These had very hard termination pieces. I suspect that the only reason that they did not have severe problems with string breakage as a consequence of the extremely hard material is that they had an unusually large radius at both contact points with the strings. > > There were some good aspects of the design. The termination pieces provided a bridge between each note, connecting the capo and the main mass of the plate. This provided a very rigid termination. > > I never cared for what the termination piece did to the sound, whether the problem was the extreme hardness, the large radius, or some other variable. There is a reason why so few harden the capo, and it is not because they are too cheap. Call me an old-fogy, but for my money, hardening the capo does more harm than good. > > Frank Emerson > --- -------------- next part -------------- An HTML attachment was scrubbed... URL: <https://www.moypiano.com/ptg/pianotech.php/attachments/20110630/bf652297/attachment-0001.htm> -------------- next part -------------- A non-text attachment was scrubbed... Name: ptr.custom.capo.jpeg Type: image/jpeg Size: 17818 bytes Desc: not available URL: <https://www.moypiano.com/ptg/pianotech.php/attachments/20110630/bf652297/attachment-0001.jpeg>
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