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rib crown radius

  • 1.  rib crown radius

    Registered Piano Technician
    Posted 09-17-2018 12:55
    Does anyone know for exactly what the rib crowning radius (or how much rise is cut into a 1 meter rib will suffice) for various piano builders who use crowned ribs: Hamburg Steinway, Bos, Fazioli, etc.  

    Not so much looking for speculation but rather if any one has any data that's reliable.  

    Thanks

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    David Love RPT
    www.davidlovepianos.com
    davidlovepianos@comcast.net
    415 407 8320
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  • 2.  RE: rib crown radius

    Registered Piano Technician
    Posted 09-17-2018 16:10
    I saw someone who makes a great piano try drawing a 60' radius on their shop floor. First with 60' of piano wire, then 60' of pvc pipe. Not satisfied went to a cad drawing with marks every 1/16".

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    Larry Messerly, RPT
    Bringing Harmony to Homes
    www.lacrossepianotuning.com
    ljmesserly@gmail.com
    928-899-7292
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  • 3.  RE: rib crown radius

    Posted 09-17-2018 17:38
    I had a machine shop with a laser cut a 6' pattern out of aluminum for me years ago @ a 60' radius​. 3 ft = 1/4" +/-
    -chris

    ------------------------------
    I don't always play the piano, but when i do, I prefer my own.
    chernobieffpiano.com
    grandpianoman@protonmail.com
    865-986-7720
    ------------------------------



  • 4.  RE: rib crown radius

    Registered Piano Technician
    Posted 09-17-2018 19:20
    Neither Steinway or Fazioli crown their ribs. Both use a crowned press. Steinway holds the curvature of the press as a proprietary trade secret.

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    Karl Roeder
    Pompano Beach FL
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  • 5.  RE: rib crown radius

    Registered Piano Technician
    Posted 09-18-2018 01:13
    NY Steinway does not.  Hamburg Steinway does.  Don't know about Fazioli.

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    David Love RPT
    www.davidlovepianos.com
    davidlovepianos@comcast.net
    415 407 8320
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  • 6.  RE: rib crown radius

    Registered Piano Technician
    Posted 09-18-2018 08:46
    Mr.Love,
    According to my friend and mentor Juan Toribio, who does belly work under warranty for Fazioli and has sat with Mr. Fazioli getting instruction on their soundboards, they do not. When asked about rib crowning Paolo Fazioli was said to reply "we tried that, it didn't work". You and I have gotten different information regarding Hamburg ribs. As I'm usually wrong in such disputes I'll do some more research.

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    Karl Roeder
    Pompano Beach FL
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  • 7.  RE: rib crown radius

    Registered Piano Technician
    Posted 09-19-2018 09:47
    When I was in Italy in 2011 teaching a seminar at the AIARP conference, it was attended by someone from Steinway Hamburg. I was discussing flat and crowned ribs pointing out the Steinway used flat ribs (meaning NY Steinway) and the Hamburg Steinway rep clarified that Hamburg did in fact radius their ribs unlike NY Steinway. Baldassim or Gravagne who have both spent some time at the Fazioli factory might have info on whether Fazioli does or not. 

    But my my question wasn't so much who does or doesn't, it was for those that do, what is the typical radius they cut the ribs to. The 60' circle has been used as a talking point standard for lots of years but it is unclear whether that represents the radius rhat ribs are cut to or trying to achieve post compresssion. A 60 foot radius (18.28 meters) achieves crown rise over 1.1 meters of about 8.5 mm (about 1/4"). That's appximately the length of the longest rib in most pianos. But some belly folks radius the ribs at a much larger radius on the order of 32 or even 45 meters which gives much less rise from the cutting of the rib, again the remainder being achieved by compression. NY Steinway, and some others, as pointed out, start flat and achieve crown purely through compression. 

    So I was asking for those manufacturers that radius the ribs and use compression for crown formation what is typical. The RC&S method is different and I understand that process, though I don't use it.

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    David Love RPT
    www.davidlovepianos.com
    davidlovepianos@comcast.net
    415 407 8320
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  • 8.  RE: rib crown radius

    Posted 09-19-2018 10:27
    ".......... start flat and achieve crown purely through compression."

    I don't think that is quite correct David.  The compression does't start until it's glued in. The crowning is a natural process of equilibrium of when two pieces of dried wood are glued together.  There's no compression while it's growing back after being artificially dried out.  Once the growth out is contained, then the compression begins.

    I think the real question is why a 60' radius?
    You may find this accidental discovery of mine interesting. For the past two years I have precut (although albeit slightly larger) the rib stock. Remember this is high grade straight grained pine. I use Eastern White pine. I noticed something peculiar. The rib stock would bow to a natural bow and stop bowing. Guess what? It was a 60' radius bow perfectly all on its own.
    Is that a coincidence?  So now i wonder if the presses were made to accommodate that natural bow. And that the intention was never to use a flat rib.
    -chris



    ------------------------------
    I don't always play the piano, but when i do, I prefer my own.
    chernobieffpiano.com
    grandpianoman@protonmail.com
    865-986-7720
    ------------------------------



  • 9.  RE: rib crown radius

    Registered Piano Technician
    Posted 09-19-2018 15:42
    Chris,

    Very interesting.  You could be on to something very logical.

    It could be that in the "old" days, the factory guys noticed this phenomenon, decided to figure out the radius, did so, and voila!...from that time on the "standard" answer became: "Radius of a 60' circle".

    This actually makes a lot of sense (to me anyway).

    Pwg

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    Peter Grey
    Stratham NH
    603-686-2395
    pianodoctor57@gmail.com
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  • 10.  RE: rib crown radius

    Registered Piano Technician
    Posted 09-19-2018 18:41
    I meant through expansion of the panel once the ribs are glued to it and the panel rehydrates, but I assumed that was understood when I used the term compression.

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    David Love RPT
    www.davidlovepianos.com
    davidlovepianos@comcast.net
    415 407 8320
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  • 11.  RE: rib crown radius

    Registered Piano Technician
    Posted 09-19-2018 18:43
    I would say it's pure coincidence. One of those correlation/causation fallacies.  Think about it. That would mean that they would have wanted to insure that the rib was placed on the panel mindful of which way it was going to warp. That seems highly unlikely.  Not to mention that my experience with ribsstock is different. They don’t warp as they change emc unless they are stored in such a way as to encourage it. 

    More likely, in my view, the 60’ radius came into being as a reasonable amount of crown so as not to have the bridge contact the struts, a ceiling, as it were. And a floor for that matter. The knowledge that you could increase impedance by compressing a dome shaped spring was probably accompanied by the question of “how much will we likely need”.And the answer was, “well not that much but some. Let’s try a 60’ radius.” “OK let’s.” 

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    David Love RPT
    www.davidlovepianos.com
    davidlovepianos@comcast.net
    415 407 8320
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  • 12.  RE: rib crown radius

    Posted 09-20-2018 10:07
    • Chris C. wrote:
      "I don't think that is quite correct David.  The compression does't start until it's glued in. The crowning is a natural process of equilibrium of when two pieces of dried wood are glued together.  There's no compression while it's growing back after being artificially dried out.  Once the growth out is contained, then the compression begins."
    • Compression starts after the ribs have been glued to a dried panel and the soundboard is exposed to normal room humidity levels (of course, presumably RH levels above those in the soundboard panel drying box). This compression will occur prior to the soundboard assembly being glued into the piano case. If one has difficulty understanding this concept, one only has to consider the NY S&S case where flat ribs are glued to a dried panel. Once such a soundboard assembly has equilibrated with the (greater RH) room environment, but prior to gluing the soundboard to the piano rim, the soundboard will develop crown. When the soundboard has its crown, the ribs will be bent into some radius. It requires force to bend the ribs, the source of that force bending the ribs is the compression occurring in the panel.

      David L. wrote:
      "I meant through expansion of the panel once the ribs are glued to it and the panel rehydrates, but I assumed that was understood when I used the term compression."

      I'm thinking that was not understood.


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    Terry Farrell
    Farrell Piano Service, Inc.
    Brandon, Florida
    terry@farrellpiano.com
    813-684-3505
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  • 13.  RE: rib crown radius

    Posted 09-20-2018 10:44
    There's only compression when it can no longer expand. But, if your convinced otherwise Terry, Glue some ribs onto a panel, set it aside, and when it reaches equilibrium, document the compression ridges for us. 

    I have also in the past glued a dry panel (before the crown fully developed), "flat" in a piano. Expecting it to crown, It didn't. I'll never do that again.
    -chris

    ------------------------------
    I don't always play the piano, but when i do, I prefer my own.
    chernobieffpiano.com
    grandpianoman@protonmail.com
    865-986-7720
    ------------------------------



  • 14.  RE: rib crown radius

    Posted 09-22-2018 17:07
    Chris C. wrote:
    "There's only compression when it can no longer expand. But, if your convinced otherwise Terry, Glue some ribs onto a panel, set it aside, and when it reaches equilibrium, document the compression ridges for us."

    The panel cannot expand where it is glued to a rib, and is thus experiencing compression. In your example above, why would compression ridges necessarily form? Maybe they would, maybe not - probably not as the strings would not be adding the additional compression in the panel that the panel would when installed in a piano.


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    Terry Farrell
    Farrell Piano Service, Inc.
    Brandon, Florida
    terry@farrellpiano.com
    813-684-3505
    ------------------------------



  • 15.  RE: rib crown radius

    Posted 09-22-2018 17:22
    Make an index with 2 nails and a stick.
    Make two holes when the panel is removed from the press.
    When the panel hydrates, the holes will no longer line up. They will be wider than the index. That's expansion.
    Only when the panel is glued to the rim, does the compression begin.
    -chris





  • 16.  RE: rib crown radius

    Posted 09-23-2018 05:14
    "Make an index with 2 nails and a stick.
    Make two holes when the panel is removed from the press.
    When the panel hydrates, the holes will no longer line up. They will be wider than the index. That's expansion."

    Correct.

    "Only when the panel is glued to the rim, does the compression begin."

    How does the first statement lead to the second?

    Anytime the panel is trying to expand (as when it gains moisture) - and is restrained - either one side (as in ribs glued to it) - or, as you point out, it is glued to something more solid at the edges - will it develop compression. The only difference one would see in these two examples is that when restrained from expansion on one side, the panel will develop a convex curve on the opposite side (what we call crown).


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    Terry Farrell
    Farrell Piano Service, Inc.
    Brandon, Florida
    terry@farrellpiano.com
    813-684-3505
    ------------------------------



  • 17.  RE: rib crown radius

    Registered Piano Technician
    Posted 09-19-2018 18:04
    Mr. Love,
    Thank you for making me look into this. My sources in NYC continued to assert a non crowned rib so I queried Hamburg. Mr. Hartwig Kalb Director of product services was kind enough to inform me that Hamburg does indeed crown their ribs. You should reach out to him and see if he is willing to give you the information you seek. It has always confused me why piano manufacturers hold this sort of thing in such secrecy. In the automotive industry for instance the manufacturers can't wait to tell you in minute detail about engineering and production advances they have made. If you can't get an answer from Steinway you might try asking Chris Maene in Belgium. He seems to be pretty well acquainted with the Hamburg factory and probably studied their designs and methods as he was working on his own.

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    Karl Roeder
    Pompano Beach FL
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  • 18.  RE: rib crown radius

    Registered Piano Technician
    Posted 09-19-2018 18:38
    Thanks Karl!  I think there are long standing traditions, especially in Europe, about "trade secrets". Even while I was teaching this seminar people expressed some surprise that I was so willing to share with them how I did things.

    While I don't intend to just hand over the spread sheets that I use and that took quite an effort to develop for soundboard design and action design and component matching and balancing and smooth weighting I probably will just give this stuff away at some point when I'm too tired to care. Not quite there but will be at some point. 

    Anyway Ill make those inquiries, thanks again for checking.

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    David Love RPT
    www.davidlovepianos.com
    davidlovepianos@comcast.net
    415 407 8320
    ------------------------------



  • 19.  RE: rib crown radius

    Member
    Posted 09-21-2018 12:33
    Interesting quote by Paolo. Here are some random quotes by piano builders
    I worked in a shop and rebuilt the soundboard press for Dale. 
    You probably know Dale. His boards are rib crowned and glued in a dished caul and dried before installing for a compression crown. He also uses the finest Sitka spruce you can find. I thought his boards became too stiff. I liked the ethereal sound of some of his early boards. A board not so constrained will have a higher amplitude of movement and the computer model pooling frequency Paolo showed in the Fazioli class at the Salt Lake convention would intuitively be lower. Better smoother bass. 

    Dale always wondered why in a board of fine straight grain,, the bass corner board was a weak piece of spruce. He must have decided that was needed to free up the bass because I saw a recent board he did and the bass corner piece was just that cruddy spruce.
    Also, tall skinny ribs were better than wide flat ribs. I find this to be true in pre WW1 uprights. The boards with tall ribs still have life. 

    Dale heard Steingreabber say Dale's piano sounded like his. Dale thought, funny I thought his piano sounded like mine. All I got was the synopsis of the short discussion. With the language barrier, what came back was,, Steingreabber said,, What do you do with the long bridge? 
    Right? He was indicating the bridge is a long rib that gets tied to and affects the structure. He uses sand to see the board vibration patterns. I don't know if he actually crowns his bridge.
    I think,, the bridge should be crowned to some degree. To build a board with crown and then flatten it with a center ridge beam would seem to remove the ability of the board to move. 
    However, free wheeling is not a good thing and the reason for shock absorbers on a car. The board can move too much. 

    A board that moves too much is what I thought of Sauter's board at the piano store in Berkeley. The sound erupted on the jazz player. He had a hard time controlling the soft dinner jazz sound. Airplane designers, they use only a straight rib and the lightest construction. Sauter was there and said it compromises the wood strength to cut through the grain and crown the rib. They high tech glue their board in a dished caul for the crown. 
    I was asking about sound transmission of the glue,, He said epoxy would be like pouring lead into his board.

    I took Nick G's class and found out why the board I modified in a Schimmel upright had a double boom. No back posts so I put in a cutoff bar and fish. Then I thinned the board down so it wasn't so stiff. When you hit it, it would boom and then wah whoom! Impedance feedback. That piano was too loud, I put wiekert felt hammers on it.,,,, Now that it has been there for 8 years,, it has mellowed. Sounds beautiful. 

    Boards seem to work in a variety of design and have different sound. It is trial and error.

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    Keith Roberts
    owner
    Hathaway Pines CA
    209-728-2163
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  • 20.  RE: rib crown radius

    Posted 09-21-2018 23:59
    Keith, I enjoyed this post. Thank you for sharing.

    Especially this part:
    "I liked the ethereal sound of some of his early boards. A board not so constrained will have a higher amplitude of movement and the ....... frequency .............would intuitively be lower. Better smoother bass."

    Sure refreshing to hear someone else say it for a change.
    Thanks,
    -chris



    ------------------------------
    I don't always play the piano, but when i do, I prefer my own.
    chernobieffpiano.com
    grandpianoman@protonmail.com
    865-986-7720
    ------------------------------



  • 21.  RE: rib crown radius

    Registered Piano Technician
    Posted 09-23-2018 20:18
    The problem with these sorts of conclusions (all of them) is that they suffer from confirmation bias: we create a grand theory or hypothesis and then look for evidence (usually empirical or anecdotal) to "prove" ourselves right. The greater discipline, the necessary discipline and the more difficult challenge in any scientific inquiry, is to commit ourselves to proving that we are wrong. And even after we have exhausted all known possibilities and failed to prove ourselves wrong we can never be sure because we can never be confident that what we need to know to prove ourselves wrong isn't something we haven't yet thought of. We usually pursue these lines of "knowledge seeking" or reasoning not to find truth, but to reassure ourselves in the face of our own ignorance.

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    David Love RPT
    www.davidlovepianos.com
    davidlovepianos@comcast.net
    415 407 8320
    ------------------------------