Another good reference on belly work that I just came across is attached, authored by Del, and comes from the September 1992 newsletter of A Michael's Pianos. It includes details on soundboard cracks and compression ridges that can accompany compression crowning, which was a very appropriate topic for that time frame when Michael Yeager had some issues with Steinway & Sons on the topic.
Del's article helps one appreciate how many variables go into the approach of "compression crowning" that has been highlighted in this thread, and in the articles. A real art. You have to consider wood density, thickness, temperature, glue type, timing, number and types of ribs, and more. The article indicates that there are alternatives to compression crowning that do not come with some of the negative baggage of compression crowning -- any elaboration?
What about bridge work within the belly process? Chris indicated that the wood type for the cap is significant. How is the bridge height achieved? When is the bridge glued in place, and is height (down bearing) now always adjusted from taking wood off the top of the bridge? (I was of the impression that previously wood might have been removed from the bottom of the bridge for fine down bearing adjustment before gluing.) Regards, Norman.
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Norman Brickman
Potomac Piano Service
Potomac, Maryland
potomacpiano@verizon.nethttps://potomacpiano.com(301) 983.9321
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Original Message:
Sent: 09-05-2024 14:54
From: Norman Brickman
Subject: Belly Work
Thanks to all for the posts. Informative, as hoped, and reinforces how complex the topic gets and covers some of the options that are part of soundboard manufacturing and re-manufacturing.
A few references that others might also find of interest: (a) the PTG Journal of January 2006, page 12, article by Mary Cushing Smith includes discussion of several factors/options in belly work. (b) in the PTG Journal of October 2006, page 16, Robert Grijalva discusses an approach for getting more power and consistent timbre in the treble. And (c) Del has some good comments in https://forum.pianoworld.com/ubbthreads.php/topics/1126038/what-is-belly-work.html that explain how the approach I referred to earlier of starting with 4.0% moisture content of flat soundboard and ribs can result in a well-tensioned crowned soundboard.
Chris, your videos are quite a good set of references for belly work and I encourage others to also have a look. The listing is at https://www.youtube.com/@ChernobieffPiano/videos.
Del, yes – consider offering again your belly work 3-hour review class. I'm sure it is a good start on the topic. And to ask again, if you or others have videos, or good references, they would be appreciated. I might give the Wolfenden treatise a try. Regards, Norman.
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Norman Brickman
Potomac Piano Service
Potomac, Maryland
potomacpiano@verizon.net
https://potomacpiano.com
(301) 983.9321
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Original Message:
Sent: 09-04-2024 23:00
From: Chris Chernobieff
Subject: Belly Work
Hi Mr. Brickman,
Its such a big question i think your going to get such varied answers that you'll most likely be more confused than before you asked it. I'll address a couple things you mentioned.
Weak treble: It sounded like you were talking about a Steinway. Compared to other companies they are one rib short in the treble and on top of that, the diaphragmatic system weakens that area badly. And further, they set downbearing incorrectly at the factory. If you check the downbearing its most likely 2+ degrees. Way too much down force on the weakened structure. If your working with an existing board, just correcting the downbearing is a good start. What i do to get a fantastic treble is replace the maple caps with a harder wood. I use Osage orange, but there are other species that work too. I believe boxwood is used a lot because of its ultra fine grain. I also like to extend the scale a little bit, my preferred length of #88 is 54mm. Then after that its good regulation of the action, and voicing properly.
The other point i'd like to make Norman is about design. No one else talks about it, but the most important elements are weight and space and internal stress. Only the Compression Crowned soundboard maximizes those three elements. All the other systems make compromises on those elements. I think the criticism of compression crowned boards come from not knowing how to make them properly. BTW, they already have a full crown before being glued in and develop compression once glue in. Making them is a timed sequence that also has to be in the proper order, when done so, they can last as long long time. When installed improperly can fail rapidly. Since i have studied over 500 soundboards one thing becomes clear, all boards are made with mistakes as far as rib dimensions, panel thicknessing and more. Its actually a great opportunity because they can be improved on by a lot. One element that offers much improvement on is weight. I can remove 3 - 8 pounds of weight from a soundboard without compromising its strength. That's because most boards are overbuilt by that much. I picked up on this when i had three sequential Baldwin R's in my shop and each boards weight varied from 12 lbs to 18lbs. And its the same with the other brands as well.
Anyways, i have around a 100 videos on soundboard design, making them and with many experiments on my youtube channel if you want to learn more about how to make soundboards. There's a lot of practical info there.
All the best!
-chris
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Chernobieff Piano Restorations
Inventor of Inertia Touch Wave (ITW)
Advanced Resonant Compression Engineered Soundboards (ARCHES)
865-986-7720 (text only please)