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On topic, Can these substances be removed should someone need to do so, and by what means?

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With great difficulty. I would not want to try. If the time comes...replace (IMO).

You could sand it off. In fact the top layer of epoxy gets sanded flat so it can be done. The problem is when you get to the wood, much softer material. Hard to get just the epoxy off and not wood.

Peter Grey Piano Doctor

Last edited by P W Grey; 02/07/21 04:23 PM.

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The third time I did this (on a 1965 Baldwin L), I botched the epoxy mix, and ended up with a gummy concoction on the soundboard that was just not going to harden. I think I used equal parts resin and hardener -- it had been a while since I had used the product, and _thought_ I remembered the mixing proportions. The whole mess needed to be scraped off. Not a happy memory. The final result, however, after the correct epoxy mix had been used, was very pleasing.


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Originally Posted by Floyd G
The third time I did this (on a 1965 Baldwin L), I botched the epoxy mix, and ended up with a gummy concoction on the soundboard that was just not going to harden. I think I used equal parts resin and hardener -- it had been a while since I had used the product, and _thought_ I remembered the mixing proportions. The whole mess needed to be scraped off. Not a happy memory. The final result, however, after the correct epoxy mix had been used, was very pleasing.

Now I'm gonna have nightmares

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This is one good reason why I don't use WS epoxy. My brain has difficulty with anything other than a 1:1 ratio. Granted, S3 Clear Coat is 2:1 and I have had to make major emotional adjustments in order to handle that...but even though it's often more than I need (like for a small piano) I will just dump the entire contents of both bottles in to the mix. That way I know the proportion is right.

BTW on a related note, when mixing large proportions of this kind of stuff (slow during, thin viscosity) it is important NOT to do it in a confining container (i.e. a fairly tall one that makes mixing easier) but rather a lower, wider, more open container. Reason being that in the smaller space the mixture will begin generating heat faster which will accelerate the curing process which will leave you less time to apply it as desired (DAMHIK). Use an open wide container that leaves the mix shallow. This will give maximum time for brushing.

Peter Grey Piano Doctor


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The tuning Fork demonstration was mentioned. I was wondering if there is a word or name for the acoustic phenomenon that describes that.
What does the adding of tension do?

-chris


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Chris
Gravity is a phenomenon, but wave motion is well understood or string scales and tuning would not be possible. I don't know of an official name for such a test, it does demonstrate wave motion in a yardstick. Piano ribs too.
I looked at the book you mentioned.
I strongly suggest looking at a physics book, here's a good one Arthur Beiser physics 2ond edition, here is a line from the wave motion section, "waves carry energy from one place to another without any actual transport of matter" that's cool.

What tension? or where and how.

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Chris
By the way this thread shouldn't commandeered it is "impolite" maybe you can start a new one Re: wave motion in pianos. Ask the question and see.

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I was on topic just presenting a counter argument against the process. It adds weight, it plasticizes the wood. It disturbs the acoustic functions (nodes,anti-nodes, drivers), it doesn't replace crown, nor does it add any internal forces that enhance sound (your tuning fork/paint stick example).
So if this thread was just about how to mix epoxy properly. Then my apologies.

-chris

Last edited by Chernobieff Piano; 02/09/21 11:44 AM.

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Well,,,,I had to respond to the soundboard things you were going on about right from page one.
Experiment!
Now suppose one has the same amount of said epoxy on the SB, and the same amount cured and in a baggie, and this baggie is placed on a tuned grand bridge, you know? here and there do you think that the difference would be audible? that tiny amount of weight , Hmm-mm--could be?
I wonder.
Maybe this should be tried, maybe you already did!


How? does this epoxy "disturb" acoustic functions.

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Little "hot dog" sand bags on the bridge would answer this in short order.

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I don't think anyone is saying that this epoxy treatment is anywhere near as good as a good replacement. Simply an alternative where re placement simply is not an option.

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Huff.... Hrmphhh!!! Chris?

It adds weight. Ok - how much weight? Is the addition of that weight as a fully distributed coating significant? If so, why?

It is not at all clear that it plasticizes wood. Start by defining the terms so that your assertion will be coherent. How much of the wood does it plasticize? Why would that be a bad thing?

Disturbs the acoustic functions? How do you know that? Do you hear them complaining? What exactly is it doing to the nodes, antinodes, and drivers?
No one has claimed that it replaces or restores crown, so why do you bring that up?

What do you mean by "add internal forces"?

The epoxy is there to stiffen the panel. Old boards lose stiffness as they lose crown. Likewise, you can add riblets to selectively stiffen the panel


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Huff.... Hrmphhh!!! Chris?

It adds weight. Ok - how much weight? Is the addition of that weight as a fully distributed coating significant? If so, why?

How much stiffness are you getting for the added weight? And what was the weight before adding epoxy? My concern would be adding more weight to an already heavy board. Which is quite common. Isn't a common trait among fine acoustic instruments the fact that they maximize a strength to weight ratio?

Quote
It is not at all clear that it plasticizes wood. Start by defining the terms so that your assertion will be coherent. How much of the wood does it plasticize? Why would that be a bad thing?

Again, for fine acoustic instruments, isn't the woody tone of spruce one of the main reasons that spruce is used? The experiments that i have done with epoxy does not indicate tonal improvement. Traditionally, a finish/coating was for aesthetics and protection.


Quote
Disturbs the acoustic functions? How do you know that? Do you hear them complaining? What exactly is it doing to the nodes, antinodes, and drivers?

Wherever a driver is located the epoxy coating will move it further away from the bridge and closer to the rim. Which is the exact opposite of what you want to do. One observation I have from my last two boards with correctly aligned drivers is the projection of sound seems increased, and the instrument sounds bigger across the room.

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No one has claimed that it replaces or restores crown, so why do you bring that up?

To help provide information to newbies that it doesn't.


Quote
What do you mean by "add internal forces"?

The example was brought up regarding the tuning fork glued to a piece of spruce demo. This of course adds tension to the spruce along the grain and you hear the volume increase. This principle is called a true crown and was used by the Ruckers in their harpsichords via angle rims. The similar principle is compression crowning across the grain. In the modern piano the compression of the panel adds to the tone. Adding stiffness via epoxy does not have that result.

Quote
The epoxy is there to stiffen the panel. Old boards lose stiffness as they lose crown.


BTW, adding a compressive force adds stiffness without adding weight.


Quote
Likewise, you can add riblets to selectively stiffen the panel.


Riblets are more for correcting a board design flaw than anything else. Even the inventor preferred not to use them unless absolutely necessary. Its amazing how many boards have incorrect rib spacing and wrong rib dimensions.


Thanks William,

-chris


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You have not answered the question as to how much weight it adds. It obviously adds weight to a board. The question remains if the added weight is a significant deficit. Since epoxies harden at close to 100% solids, then it would not be difficult to get a reasonable approximation, even after scraping and sanding the epoxied surface to level it. There is a "cost" to the added weight, how does that balance out in a cost benefit ratio with the added stiffness? Epoxies are widely used in composite structures to stiffen them, their use with carbon fiber in a matrix is the most obvious example. An epoxy surface finish forms a hardened shell with the spruce panel that stiffens it, the epoxy that penetrates into the cells near the surface forms a composite structure, those outer cells will be stronger than the wood by itself. The other wood cells not touched by the epoxy retain their characteristics. I submit that, while an epoxied panel will weigh more, it improves the strength to weight ratio. In a particular circumstance (like an old board), the benefit is worth the cost.

You have not defined your terms as to what constitutes plastisized wood. As such your claim is incoherent. As for tonal benefit, my mileage varies from yours. The stiffened panel gains sustain and dynamics in age compromised boards, I am making no claim that the benefits meet or exceed those of a new board. Nor is anyone else, from what I gather. Yes, finishes are used for protection and appearance. Epoxies do that and also stiffen the panel.

"Wherever a driver is located the epoxy coating will move it further away from the bridge and closer to the rim." You make this comment as if it were a statement of fact, but you have offered no evidence to support this assertion. How does a driver get "moved" by an epoxy coating closer to the rim? That makes no sense. What driver are you talking about?

Strictly speaking, the induced crown adds tension to the wood along the grain on the top surface where the tuning fork has been attached, the tuning fork does no such thing. There will also be compression on the underside of the panel.

No one disputes that compression crowning helps create the tone in that a good compression crowned board will have good dynamics and sustain. It does so by making the panel-rib combination much stiffer. Epoxy also makes the panel stiffer and there is attendant improvement in the tone. Results are similar but not the same; I am not arguing that they are equivalent.

You seem to be arguing against the use of riblets, saying that they are used to correct design flaws. Didn't you add riblets to a very small grand that you installed a new board recently? You wrote about it in a post. What design flaw were you working to overcome?


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Your SB invention is mysterious and very different than the normal approach.
Hey! we need to ask questions.

Your insistence that all other SB's are wrong without proof is ludicrous. "very"
Everything is no good, the wood, the glue, the ribs, the whole sb design, and the finish too and yes that gets my attention, this false information.

I do not remember badmouthing your invention the way you consistently criticize everyone else's efforts.

I really don't follow your approach it is so far off the normal and what I/we are used to. this loudspeaker type application.

Asymmetrical calculations on a musical instruments SB doesn't make sense, that is used in architectural applications, but if there are some who say, Jesus!! that sounds better than anything I've ever heard, then ok.

I talk about wave motion because it is the foundation of sound, and most instrument makers know this, to disregard the physics is bizarre. And refusing to answer some scientific questions about your SB invention leaves one with more questions and mystery.

Do you think the info in physics books is incorrect also, RSVP.

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Blaisguitars,


Regarding the topic, I merely pointed out the negatives of using epoxy, you are welcome to use it and point to the positives.


-chris


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Asymmetry in soundboard design and construction is not particularly new.

Young Chang makes its soundboards whereby the panels are tapered asymmetrically, and where the ribs are crowned by CNC machines asymmetrically.


Chris's idea of asymmetrically centering the thickest part of the rib under the bridge makes sense, as the down bearing forces of the string press down on the bridge there. Asymmetrical thicknessing of ribs is fairly commonplace in guitars, particularly with parabolic ribbing.

One school of thought has the bridge centered as much as is possible. A well located and curved bass cut off bar allows this for most of the ribs. The shape of the rim and the edge of the belly rail necessarily offset the bridge more and more as one approaches the ends.

I have heard great sounding boards made a multitude of ways. If it pleases a lot of musicians and pleases yourself, then it can be considered a success.


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Chris,

How many boards have you treated with epoxy?

I use a number of approaches in rebuilding and this is one of them. As I said in the beginning of this tread, epoxy treatment will not fix a failed board, but it will improve an already functioning board. If I didn't feel there was a benefit, I certainly wouldn't use it. I am slightly sensitive to epoxy so if I can use a different approach I will.


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Will,
Yes, uneven on both sides. Wavelength manipulation.
I had to look under the centennial D we have and several ribs midway are even on both ends the taper and thickness and the usual about 1'x1' square. Ribbing isn't always asymmetrical, in some SB's I guess.
I do agree with your philosophy.

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