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Thanks everyone who has been helping me thus far with my Baldwin Model G learning/restoration project. In my previous thread I detailed out my plans with the bridges (repair small splits with epoxy.)

Next problem:
While my soundboard does have crown (approx 1/16" when measured with a string). The middle of the long bridge, unfortunately has negative downbearing (by about 1/16", or ~1/2 the width of the aliquot bar at note 44 and ~0 at note 23).

I find it odd that there is crown but no downbearing…

I know the CORRECT answer is to replace the soundboard and go again. For those who are just tuning in, I’m doing this as an educational project on a piano which would otherwise be headed for the trash heap. I already have a lot on my plate and don’t really want to take on a soundboard replacement.

That said, I obviously don’t want to go forth and spend a bunch of effort without at least some chance of being successful.

What are some options here?

I know Igrec talks about cutting a vertical cut in the bridge and inserting a shim. Seems pretty invasive but do-able.

When I pull and reinstall the plate, could I install the plate SLIGHTLY lower to a happy medium (where there is at least a minimal amount of downbearing throughout the bridge?
Is there another option? Again, this is an educational rebuild (with the hope of a functional instrument at the end.)

Thanks in advance!

Last edited by A-Piano; 01/26/21 08:25 PM.

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I believe you may have an imaginary crown there. The longest rib you should measure is most likely about 42" long, with a 1/16" "crown" that would be a 295 ft radius. In other words flat as a pancake. It should be .30" (not .062") which would be equivalent to a 60 ft radius . That would explain why your bridges no longer have downbearing.


-chris

Last edited by Chernobieff Piano; 01/26/21 09:09 PM.

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Chris, you are correct on the 42" part. I had been told any sort of deflection would be considered good. The loss of nearly 1/4" would certainly explain the lack of downbearing.

From my reading (short of replacing the soundboard) the correct response would be to set downbearing to 0 and call it a day, correct? I assume i can do this by shaving the dowels which support the plate and adjusting the pinblock/case fit? (My pinblock rests on a lip of the case but is not attached on any sides).

Thanks!


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If I recall you were going to do a roll pin conversion, that would be your best shot for minimal bearing. But even in that case expect a somewhat choked board.

Maybe an option would be to convert with agraffe bridges that don't require downbearing? I've never used them myself and it would be experimental. Maybe other techs here have used them and can comment on their pros and cons?

-chris


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Chris - there were a couple folks who were recommending a roll pin conversion, I was leaning towards not since it is adding a lot of work to an already big project. Of course if it is the easiest reasonable solution, I might reconsider. My concern with that solution would be that I will end up with positive (or zero) downbearing on the back of the bridge, but still have negative downbearing on the front.

My thought for lowering the plate to achieve ~0 downbearing was that I could maintain equal downbearing on both the front, and back of the bridge.

I'm also reading more into Igrec's controversial shimming technique. (Image HERE.)
[img]https://photos.app.goo.gl/zqfkgyYmd3TGoumF7[/img]

And also into the unusual solution of coating the soundboard in epoxy (Detailed HERE.)

Of course the epoxy and lowering the plate is the easiest, but I'm wondering if it could be worth attempting the shim in conjunction. Curious if anyone else has done that.

I'm reasonably certain, whatever I do, I don't want to finish the project with negative downbearing, regardless of soundboard crown.


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I'll add something else interesting to think about (and don my flamesuit.)

The point of having downbearing on a soundboard (as I understand it) is to transfer the energy of the strings into the soundboard in a manner that allows for little loss and maximum duration of resonation.

The downbearing is essentially 'loading' the soundboard (much like a car pushes on a leaf spring). So, in theory, wouldn't having negative downbearing be BETTER than 0 downbearing.

With 0 downbearing there is no 'preload' on the soundboard and it is allowed to sit where it naturally wants to sit (at rest).

With either positive OR negative down bearing you are applying pressure to the soundboard, thus pulling (or pushing) it 'taught' rather than 'at rest'. Hence my question of negative downbearing being better than none. At least there is still potential energy being applied to the board which will help maintain oscillation with the sound waves (much like a taught piano wire will resonate but a slack wire will not).

Perhaps I'm totally missing something though?


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Does the piano have strings on it, or have you removed them? I find it difficult to believe that when the strings were on, that some of them were 1/16" above the bridge.


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Hi BDB,
I would love to find out I'm doing something wrong with my measurements.

The piano has strings on it. The bass note I measured was on a random bass string that snapped a couple months ago, so I pulled thread between the tuning pin and the hitch pin and it just barely drug across the top of the bridge.

For the higher note where I measured the 1/16" I loosened the tuning pin just enough to slip the wire off the bridge pins, thus allowing it to run straight back to the aliquot bar/ hitch pin. It was only BARELY brushing a bridge pin.

I then took my metal machinist's ruler, placed the end on the top of the bridge cap (on the graphite) and observed the wire passing almost exactly in front of the 2/32" mark. If I tried pushing the wire down so it contacted the bridge cap, it would pop back up to the same position.

Unfortunately I didn't take a photo and have since put the wire back on the bridge. I can probably repeat the measurement on another string and try to get a photo, if that would be helpful.

I guess the sound board lost crown for reasons aside from too much downbearing (otherwise it would have stopped losing crown when it hit 0 downbearing)

Last edited by A-Piano; 01/27/21 02:45 AM.

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More likely the soundboard only seems to have lost its crown from the other strings pressing down on it. The bridge pins, being at an angle, can hold strings against the bridge, however. If you loosen the string enough to lift it from the bridge pins, the natural bend in it could lift it off the bridge as well. But if you took all the other strings off the piano, and put the one you observed back on, chances are it would have downbearing. After all, you do not know whether the soundboard has been that way since before it left the factory.


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Thus...I maintain that you cannot get an accurate picture of the DB/crown until/unless all the tension is off and the strings removed. Otherwise you are making ASSUMPTIONS. As an engineer you should know the pitfalls of that.

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Originally Posted by A-Piano
The downbearing is essentially 'loading' the soundboard (much like a car pushes on a leaf spring). So, in theory, wouldn't having negative downbearing be BETTER than 0 downbearing.
That's not how downbearing works in practice. Again, I have seen boards in all directions, and, for whatever reason, they all seem to work fine. Most of the concepts about soundboards that you read about are theoretical in nature. In practice, crown and downbearing is a tonal issue. You can attach a tactile speaker to a piece of soundboard, and bend it to simulate crown and downbearing to hear the difference as you make the changes. Or, just knock on it. The main function is to help keep the strings on the bridge, although the bridge pins help, the string can ride up over time with a negative bearing.

Most of what is written about piano soundboards is marketing. Some rebuilders and manufactures make a big fuss about soundboards, but if all the string energy doesn't get into the board [and mostly stays on the string], you never get to hear the difference anyway.

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Originally Posted by A-Piano
When I pull and reinstall the plate, could I install the plate SLIGHTLY lower to a happy medium (where there is at least a minimal amount of downbearing throughout the bridge?
If you lowered the plate, you would change the string height. If you did that, you would need to figure out if the action geometry could handle that. Lowering the plate likely would require a redesign of the action to accommodate the change.

Normally, you start with the string height that you need, then adjust the height of the bridge to get the bearing that you want. But, it is guess work, as you set the bearing in an unloaded state, and in a loaded state, everything is different. Ultimately it is the loaded state that matters.

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Originally Posted by A-Piano
I know the CORRECT answer is to replace the soundboard and go again. For those who are just tuning in, I’m doing this as an educational project on a piano which would otherwise be headed for the trash heap. I already have a lot on my plate and don’t really want to take on a soundboard replacement.
That depends on who you speak with. Many people don't believe that ripping out and replacing a sounboard is the right thing to do. It is a faster and many time easier approach, but is it really correct? I doubt it. If people replace the top plate of a Stradivarius, even though it might have been completely destroyed, is that the right thing to do?

These people disassemble the soundboard, shim it, and reinstall the crown, all using the original soundboard. This is an authentic approach to long-term piano preservation. I might do things differently, but none of that really matters. The point is, this piano is being preserved. A new soundboard would make it a different piano. If he wanted to do that, he could have built a new piano from scratch faster. Their end result looks great.
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What Peter says is correct.
You can only measure what crown is there, with the load off of it. When you measure the crown with the load on it, you are measuring the boards reaction to the load.

-chris


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BDB, one of the things that I have done for several decades has been to take downbearing readings on a number of selected notes before and after destringing, so as to find out if there are any changes as the downbearing pressure is released from the board. The changes in values can vary widely from piano to piano, and the changes in downbearing can vary widely within an individual instrument. I use a Fowler dial gauge to do so. This has three feet, two fixed feet on the ends and the one in the middle goes up or down and a corresponding change is shown on the dial. Typically, I take 12 or 13 readings per piano. Sometimes all notes will show changes in bearing values, other times most notes will show some rise in downbearing values with all other strings removed while some notes will indicate no change at all after the strings are removed. That is most often in and around the killer octave area.

As for crown, at those times I would use the string method to check for crown in many places, but did not quantify what I saw. These days, I have a foot long straight edge with a dial indicator attached where values can be gotten before and after. I take these readings between as many ribs as are accessible (not blocked by beams). Combine the bearing and crown readings and it will give you quantifiable information about the health of the soundboard.

So the answer to your observation about there being positive downbearing after destringing is that this is true most of the time but not always.

Piano 411, side bearing of the string through the bridge pins also serves the function of having enough deflection angle such that the speaking length is sufficiently restrained that it can have enough of a defined termination so that not too much energy bleeds past the bridge pins. Where the deflection angle is sufficient, we can get that clean tone with well defined pitch that we all recognize, with too little side bearing too much energy bleeds past the terminating pins, with buzzing and other distortions the result.

The big fuss that some makers and rebuilders make is all about maximizing the amount of energy that gets into the vibrating panel, and then conserving that for as long as possible. Doing that well is built on a multitude of well executed details. There is nothing wrong with marketing that mastery when it can be achieved in a piano.

Lowering a plate to increase downbearing is almost always done by trimming the shelf or dowels at the tail end of the piano. Unless there is a very good reason based upon manufacturing defects, one would never lower the plate by thinning the pinblock. The effect on string height is relatively minor at the tail end, it is great when one thins the pinblock.

No one I know who rebuilds re-designs an action based on simply lowering the plate at the tail end. The lowered plated does affect the string height and we should as a matter of course be aware of such changes. You are however, overstating the impact it has on the functioning of the action in practice.


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I misspoke in the above post. I wrote:
"So the answer to your observation about there being positive downbearing after destringing is that this is true most of the time but not always."

That should read: Mostly you will get a positive downbearing reading, but not always. The downbearing reading under load may register zero or negative, and not change at all once the string load has been released. There will be circumstances where the reading will come up, and circumstances where it goes further negative. Sometimes the strings are holding the board up, after release of strings, the board oilcans and collapses. When that occurs, the board is toast.


Some soundboards leave the factory in a defective condition. Most don't. We can't know exactly what condition it was in when it left the factory. At the other end of the clock, we do the best we can to determine the changes in health of the soundboard, based on the science we can muster and experience.


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If this is a piano that left the factory in a defective condition, and nobody noticed it in the past 100 years, what is the defect?


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I think what Will is saying is simply...it happens, not necessarily this one, just that it happens.

Anyway, since it is now 2-3 times past it's design lifespan it's irrelevant.

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Originally Posted by WilliamTruitt
Lowering a plate to increase downbearing is almost always done by trimming the shelf or dowels at the tail end of the piano. Unless there is a very good reason based upon manufacturing defects, one would never lower the plate by thinning the pinblock. The effect on string height is relatively minor at the tail end, it is great when one thins the pinblock.

No one I know who rebuilds re-designs an action based on simply lowering the plate at the tail end. The lowered plated does affect the string height and we should as a matter of course be aware of such changes. You are however, overstating the impact it has on the functioning of the action in practice.
The way I originally read OP, I understood it as him adjusting the pinblock to get more downbearing--I thought he wanted to get downbearing by adjusting the plate on the front side of the bridge. That is why I brought up the issue of the action geometry. I reread what was written, and he did say something about pinblock adjustment in relation to downbearing, but that might have just been an aside.

In any event, I agree that the effect on string height is relatively minor at the tail end, and conversely great if one were to thin out the pinblock--hence my comment about the effect on the action geometry. You are right, if you lower the plate at the tail end, the action geometry would not need a redesign.


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