Cracked plate - now what?

Posted by: BobbinBlueJay

Cracked plate - now what? - 04/17/13 10:56 PM

Because of family history and sentiment, we decided to restore my wife's hand-me-down Sohmer baby grand (ca. 1906 best guess) a few years ago. Very nice looking restoration, but it wouldn't stay in tune, so we dragged our feet on selling our other piano which was the original plan. So recently we had the tuner make a more concerted effort to tune the Sohmer over a couple visits. Then one night just sitting in the other room we hear a "bong" ring out from the piano with no one even touching it. I thought a pin slipped or something, but when he came back, we could see the cast iron plate cracked at two junctions of the frame. After some research, he said it's not repairable, so we're left with what to do next.

Is it fair to say a cracked cast iron plate can't be repaired?

Are piano's like cars? Is there a market for the other good used parts that it does have?

I'd appreciate some others' opinions what we do next.
Posted by: Scott Hamlin

Re: Cracked plate - now what? - 04/17/13 11:16 PM

Cry. Really there isn't much you can do
to repair the plate. Maybe our friend
at Nashville has some ideas....
Posted by: beethoven986

Re: Cracked plate - now what? - 04/17/13 11:50 PM

It is possible to repair plate cracks, either by welding or metal stitching.
Posted by: Dave B

Re: Cracked plate - now what? - 04/18/13 12:02 AM

Depends on how bad the tear is.
Posted by: kpembrook

Re: Cracked plate - now what? - 04/18/13 12:10 AM

Plates can definitely be repaired. People who say they can't just don't know how.
Posted by: Emmery

Re: Cracked plate - now what? - 04/18/13 12:48 AM

It requires somebody to assess how bad it is. Its a very rare skill these days for welders to pull this off but there is a company in Yonkers that specializes in this and one also out on the west coast from years back. I've seen it done by a really good welder in Toronto and he put a heat sink wrap about 8-10" away from the crack, preheated the weld spot with an oxy acetylene torch to a certain temperature (tested with thermal crayons) before laying into it with a stick welder.

This video shows it being done without the above mentioned fuss and they are claiming success with what they have done so far. For some reason it looks a bit dubious to me, don't ask me why...

https://www.youtube.com/watch?v=kRsSHShYLrY
Posted by: OperaTenor

Re: Cracked plate - now what? - 04/18/13 01:37 AM

Rod Vehrnjak is an expert at repairing cracked plates
Posted by: JohnSprung

Re: Cracked plate - now what? - 04/18/13 02:13 AM

The big question is how much sentimental value does it have?

It can be fixed, but it'll cost more than you could sell it for after it's fixed.

Absolute worst case, you could grind and epoxy the old plate to make a smooth place where the crack is, and have a foundry use it as a pattern to cast a new one. Like I said, it'll cost way more than the piano will ever be worth on the market. So, the question is how much sentimental value?
Posted by: beethoven986

Re: Cracked plate - now what? - 04/18/13 02:31 AM

Originally Posted By: JohnSprung

Absolute worst case, you could grind and epoxy the old plate to make a smooth place where the crack is, and have a foundry use it as a pattern to cast a new one.


This would be totally cost prohibitive, even for a valuable piano. A more realistic option might be to have David Rubenstein construct a new plate out of welded steel, but even that strikes me as a silly idea. Cracked plates can often be repaired, so let's just go with that.
Posted by: BDB

Re: Cracked plate - now what? - 04/18/13 02:58 AM

Originally Posted By: JohnSprung
Absolute worst case, you could grind and epoxy the old plate to make a smooth place where the crack is, and have a foundry use it as a pattern to cast a new one.


No, you cannot do that. The result will be undersized.
Posted by: David Jenson

Re: Cracked plate - now what? - 04/18/13 07:15 AM

Perhaps it's time to transfer "family history and sentiment" to a new piano.
Posted by: Larry Buck

Re: Cracked plate - now what? - 04/18/13 07:29 AM

A plate repair is always possible.

How you repair it depends on where the break is.
Cost will be the determining factor in your decision.

We just repaired two Bechsteins with the classic cracks in the strut.

One of them has been at pitch for 60 days, no problems.

Feel free to contact me. If you can take a few pictures and send them to me that would help.
Posted by: BDB

Re: Cracked plate - now what? - 04/18/13 11:25 AM

In any case, repairs will be expensive, and involve redoing much of the work that has already been done.
Posted by: Larry Buck

Re: Cracked plate - now what? - 04/18/13 01:16 PM

A question that deserves an answer is ... Why did it give out. What ever inappropriate stress brought this on, should be identified and resolved.

Expensive BDB?

Depends on your perspective.
Posted by: prenex

Re: Cracked plate - now what? - 04/18/13 01:57 PM

I'd try and find a donor piano.
Posted by: BDB

Re: Cracked plate - now what? - 04/18/13 03:26 PM

Originally Posted By: Larry Buck
A question that deserves an answer is ... Why did it give out. What ever inappropriate stress brought this on, should be identified and resolved.

Expensive BDB?

Depends on your perspective.


Expensive in relation to what has already been spent on the piano. Much of it would have to be done over.
Posted by: Scott Hamlin

Re: Cracked plate - now what? - 04/18/13 03:43 PM

Originally Posted By: prenex
I'd try and find a donor piano.


I agree. Yes it is POSSIBLE to repair
the crack .. do you really want to risk
the time and money it will cost on a
"maybe" it will hold?
Posted by: Silverwood Pianos

Re: Cracked plate - now what? - 04/18/13 03:44 PM


Originally Posted By: BDB

Expensive in relation to what has already been spent on the piano. Much of it would have to be done over.


Agreed although nothing mentioned from the OP about what was done to the instrument to “restore” and many of us have experience with the variety of interpretations contained in that word.
Posted by: kpembrook

Re: Cracked plate - now what? - 04/18/13 04:25 PM

Originally Posted By: Plinky88
Originally Posted By: prenex
I'd try and find a donor piano.


I agree. Yes it is POSSIBLE to repair
the crack .. do you really want to risk
the time and money it will cost on a
"maybe" it will hold?



A proper plate repair is not a "maybe" kind of thing. Properly done it is a reliable and permanent repair.

This is not to say that there aren't half-baked approaches that might not be satisfactory. But repairing cast iron to function under high stress loads is a well-known and established process. Remember, there are other uses for cast iron besides piano plates.
Posted by: Scott Hamlin

Re: Cracked plate - now what? - 04/18/13 04:47 PM

Originally Posted By: kpembrook

A proper plate repair is not a "maybe" kind of thing. Properly done it is a reliable and permanent repair.



So he can expect some kind of warranty
from whoever does the repair?

Yes I understand welding and stiching
are acceptable and reliable repairs.. even
in maritime apps.

Here's my concern.. SOMETHING caused this
plate to fail.. either the iron is bad or
the tension is too much.. i dont know..
either way.. Wouldn't a repair just
put you in the "same boat" - same iron,
same piano - why wouldn't it crack again
eventually? Why not just get a brand new
plate instead as an insurance policy?
Posted by: beethoven986

Re: Cracked plate - now what? - 04/18/13 05:06 PM

Originally Posted By: Plinky88

Here's my concern.. SOMETHING caused this
plate to fail.. either the iron is bad or
the tension is too much.. i dont know..
either way.. Wouldn't a repair just
put you in the "same boat" - same iron,
same piano - why wouldn't it crack again
eventually? Why not just get a brand new
plate instead as an insurance policy?


Part of the repair process would include finding out why the plate failed. Acquiring a new plate for an early 20th century Sohmer?? That's just not feasible. Even if you could find someone to cast a new one, a one-off casting would be expensive. There are a few people who could manufacture a new plate out of welded steel, but that would also be expensive.
Posted by: Nash. Piano Rescue

Re: Cracked plate - now what? - 04/18/13 07:47 PM

I had a super fancy Knabe grand come in from Baltimore last year that had a I want to say 60K dollar restoration done and when whoever went into the home to tune it the plate snapped in two spots. When it came into the shop the first thing I looked at was if something got between the pinblock and the plate or pinblock and frame of the cabinet etc.

Instead it turned out that the plate was actually dropped by whovever did the sandblasting and the crack wasn't visible until tension was put on it.

I contacted Muggy Welding who specializes in cast iron repair welding. I think it's www.MuggyWelding.com sent them a sample of the iron and they made us a high nickle content stitch welding rod and we just welded it back together. Technology has improved to where you don't need to heat the whole plate first, a mig welder can be used but even with Argon they are still messy. The stitch welding is easier to control and can be filed.

Of course the downside was all of the new strings had to be tossed and re- replaced, plate and pinblock removed. Sometimes you can use heat sink clay but I am never that lucky.

We also keep all our old plates we remove from dead pianos, we dont sell our souls to the scrap metal man because you never know who will need one. Not sure if I have a Sohmer plate in the rack or not.

Just a few thoughts for you on what actually works. There is also an iron epoxy with a 26,000 pound shear strength that a supplier sent me to try but I haven't tried it because it has a short working time, similar to the glue BMW uses to put it's cars steel panels together.
Posted by: Nash. Piano Rescue

Re: Cracked plate - now what? - 04/18/13 07:50 PM

www.muggyweld.com is the correct website sorry
Posted by: Larry Buck

Re: Cracked plate - now what? - 04/18/13 09:23 PM

Regardless of the new techniques available for cast iron repair, it is still the same material and behaves that same way it always has. You must repair it within it's limits to be heated.

Cast iron expands bi-cubically. Contracts exactly the same way.

If the iron is constrained in any way on expansion, it deforms. It still CONTRACTS bi-cubically. Take a good look at a plate ... all sorts of constraining places.

Our plate repairs were tested with a magnafulx dye and yes, we found stress cracks in the repair from time to time and they had to be redone.
Posted by: RestorerPhil

Re: Cracked plate - now what? - 04/18/13 09:40 PM

What model Sohmer?

I have a Sohmer 9B back in my shop now which I had restrung and had replaced the agraffe bridge with conventional pinning with new caps about 30 years ago. Recently the piano was damaged by a second floor plumbing leak down onto the piano in the library on the first floor. It remained wet for a week before the situation was discovered. The damage ruined the reworked bridges and made a wreck of the soundboard.

I don't think the customer is going to go for the solution: new board and bridges. If they don't, that may make a 9B plate available. This one is not nearly that old, but I don't know when the 9B model first came into production.
Posted by: JohnSprung

Re: Cracked plate - now what? - 04/18/13 09:52 PM

Originally Posted By: BDB
No, you cannot do that. The result will be undersized.


You're right. I forgot about thermal expansion. It would come up short by about an inch in six feet.
Posted by: Ryan Hassell

Re: Cracked plate - now what? - 04/18/13 11:00 PM

Not to hijack this thread, but how common of a problem is a plate cracking? I have been tuning about five years now, and have done many, many large pitch raises. Fortunately, I have yet to experience a cracked plate. I dread the day it does happen though!
Posted by: beethoven986

Re: Cracked plate - now what? - 04/18/13 11:13 PM

Originally Posted By: Ryan Hassell
Not to hijack this thread, but how common of a problem is a plate cracking? I have been tuning about five years now, and have done many, many large pitch raises. Fortunately, I have yet to experience a cracked plate. I dread the day it does happen though!


It's not common, and even less common for it to happen when you are there. One could probably go a whole tuning career without witnessing a plate crack. Just remember that if it happens, it's not your fault.... doing a large pitch raise should not cause a plate to crack unless due to faulty plate design or some other mitigating factor.
Posted by: RestorerPhil

Re: Cracked plate - now what? - 04/18/13 11:23 PM

I have only had a plate break twice. The most memorable was a Chinese stencil brand console. I didn't even have it up to pitch when it happened.

I lost that customer, plus the church she went to, plus who knows how many indirectly - all because of a plate that had obviously been installed with one of its bolts pulled too tight with nothing behind the plate in an area.

The piano had just been bought second hand - hardly used. I had just moved the piano into the home a couple of weeks earlier. The manufacturer (distributor?) offered to sell a replacement at wholesale, even though they had no obligation to this second owner. My word, plus the second opinion of another tuner was not enough: I was blamed.

The other one was an Aeolian spinet that I think I had traded in when I had a retail store about 33 years ago. For me, this has been very rare.
Posted by: kpembrook

Re: Cracked plate - now what? - 04/18/13 11:32 PM

Originally Posted By: Plinky88
[quote=kpembrook]


Here's my concern.. SOMETHING caused this
plate to fail.. either the iron is bad or
the tension is too much.. i dont know..
either way.. Wouldn't a repair just
put you in the "same boat" - same iron,
same piano - why wouldn't it crack again
eventually? Why not just get a brand new
plate instead as an insurance policy?


In almost all instances plate failure is a random problem in the single casting under consideration. You fix it because the iron was bad there. When the hidden plate defect is repaired it should be good.

The exception is where there is a known design defect -- as Larry mentioned above on certain Bechsteins.
Posted by: Ed McMorrow, RPT

Re: Cracked plate - now what? - 04/19/13 01:59 AM

I am not a fan of welding grey iron. The problem of rapid cooling in the welded area changing the carbon matrix is so hard to control.

I have repaired two different plates both with cracked struts by machining a splice over the crack that is bolted to the plate with machine screws threaded both in the splice and in the strut. I then sprayed the bronzed finish on except at the strut. Assembled and strung the piano, then filled the repair area and bronzed it when the piano was at pitch. This allows for any flexing to occur when tension is applied to the strings and then the finish will reveal any further movement that would indicate future failure. The customers were informed and assumed the risk.
Posted by: kpembrook

Re: Cracked plate - now what? - 04/19/13 02:34 AM

Originally Posted By: Ed McMorrow, RPT
I am not a fan of welding grey iron. The problem of rapid cooling in the welded area changing the carbon matrix is so hard to control.

I have repaired two different plates both with cracked struts by machining a splice over the crack that is bolted to the plate with machine screws threaded both in the splice and in the strut. I then sprayed the bronzed finish on except at the strut. Assembled and strung the piano, then filled the repair area and bronzed it when the piano was at pitch. This allows for any flexing to occur when tension is applied to the strings and then the finish will reveal any further movement that would indicate future failure. The customers were informed and assumed the risk.


Quite right. Any attempt to weld cast iron without the whole thing being heated in an oven is asking for too many variables to work in your favor. I've heard of it being done but would not consider it a reliable approach. Metal stitch is probably the most reliable--and certainly quite inexpensive, although I have successfully done the splint approach you mention, as well.
Posted by: Mark R.

Re: Cracked plate - now what? - 04/19/13 03:26 AM

Originally Posted By: Ed McMorrow, RPT
I have repaired two different plates both with cracked struts by machining a splice over the crack that is bolted to the plate with machine screws threaded both in the splice and in the strut.


Ed, if both pieces (the strut and the repair splice) are threaded, how is the machine screw going to pull them together?
Posted by: Larry Buck

Re: Cracked plate - now what? - 04/19/13 04:52 AM

I own the metal stitching products. As good as they are, they only work under certain stress conditions.

Mark R. The metal stitch is a special hooked thread requiring a custom tap. If I can make the time, I'll take a photo of the special bolt.

Cast can be very successfully welded with the proper technique. It does take time. If you work too fast, you overheat the cast and it cracks when it cools/shrinks. The first welder I used was a Navy Certified Nuclear Welder, he was good. The second gentleman I use now is highly sought after and I have to plan well ahead.

The first time consuming task in plate repair is establishing who is qualified, has the experience and is willing to work with you.
Posted by: Rod Verhnjak

Re: Cracked plate - now what? - 04/19/13 01:00 PM

I had a plate welded a few months ago. I was going to use the Lock-N-Stitch but the guys at lock-N-Stitch
told me not to use their system in my situation. They suggested welding and that is what I did with great results.
Posted by: Supply

Re: Cracked plate - now what? - 04/19/13 09:37 PM

Originally Posted By: Plinky88
Cry. Really there isn't much you can do
to repair the plate.....

Originally Posted By: Plinky88
I agree. Yes it is POSSIBLE to repair
the crack .. .

confused
Posted by: Ed McMorrow, RPT

Re: Cracked plate - now what? - 04/19/13 10:22 PM

Sorry I didn't explain it all. The splices are clamped in place for the drilling and tapping.
Posted by: Scott Hamlin

Re: Cracked plate - now what? - 04/19/13 10:39 PM

Originally Posted By: Supply
Originally Posted By: Plinky88
Cry. Really there isn't much you can do
to repair the plate.....

Originally Posted By: Plinky88
I agree. Yes it is POSSIBLE to repair
the crack .. .

confused


Oh stop with the confused. You know what
I am trying to say. Yes it can be done,
but there is such expense and risk, it
may not be worth it.
Posted by: BobbinBlueJay

Re: Cracked plate - now what? - 04/19/13 11:11 PM

Wow, thanks for all the replies. I sure stirred up a hornets nest. I get the gist of the picture: yes, or maybe, but I don't have the money to do it.

I have pics if they can be uploaded here.

Edit: Looks like there's no direct upload of jpegs? Is the only alternative to link to an image in Photobucket or the like?
Posted by: lluiscl

Re: Cracked plate - now what? - 04/20/13 02:35 AM

Originally Posted By: Ed McMorrow, RPT
I have repaired two different plates both with cracked struts by machining a splice over the crack that is bolted to the plate with machine screws threaded both in the splice and in the strut.

Exactly as I successfully repaired an old Bechstein full cracked strut (not sure if it'd work in other part of the plate).
Posted by: PianoStudent88

Re: Cracked plate - now what? - 04/20/13 02:43 AM

BobbinBlueJay, you can upload images to the Piano World servers here. After you click Submit you'll get an error page: ignore that, and check your email for the link for your uploaded picture. Then use that link for an image in your post (go to Full Reply Screen, use the fourth button from the left on the posting toolbar, and choose non-floating image).
Posted by: BobbinBlueJay

Re: Cracked plate - now what? - 04/20/13 01:36 PM

Thanks PianoStudent88. Without those instructions, I don't think I'd ever figure that out. So here goes:

Overview of the piano:


Overview of the plate:


Detail at the keyboard:


Detail of two cracks at the high end (far right end:


Detail of the crack on the left-middle strut:


It was a nice looking restoration, but all for naught now, I guess. The restoration included a new pinblock as I recall. In that last tuning, he was driving some of the pins, I believe, but he did pull the key board, etc. and support the work with large clamps.
Posted by: BobbinBlueJay

Re: Cracked plate - now what? - 04/20/13 01:46 PM

Originally Posted By: David Jenson
Perhaps it's time to transfer "family history and sentiment" to a new piano.


We already have a perfectly serviceable 1980(ish) Kawai. It was supposed to be temporary for the year that the Sohmer was being restored. Nothing special, but I guess it's the keeper now.
Posted by: John Pels

Re: Cracked plate - now what? - 04/21/13 12:57 AM

I find those cracks to be most curious because they all show me anyway that there is a bending motion taking place with that plate given that they all are opening at the top, almost like the plate was lowered at the tail end maybe to compensate for some lack of downbearing, but then no shimming took place at the keyboard end of the pinblock so that any bending motion would be offset.Either that, or it was dropped and the capo bar was the point of impact. As far as repairing cast iron is concerned, I have had a couple of plates welded with no subsequent issues. The correct process is of course to heat up the plate and then it should be tig welded using high nickel welding rods. I am lucky to have found a fabulous welder here in Houston (American Heliarc) that is pure magic with a welder and scared of nothing. He will also happily tell me when things can't be fixed.
Posted by: Nash. Piano Rescue

Re: Cracked plate - now what? - 04/21/13 01:43 PM

There is or was a gap somewhere. The last one we saw was a new pinblock which turned out to be like 1mm thicker than the one removed and aparently it wasn't checked. Could have been anything, trash in the mating surface etc. Tig welding is the same way we do them, two different types of nickle rods though. Stiffer rod on the Filet weld and a slightly softer one at the showing surface so it can be smoothed out.



I realize Cast iron is the most ridgid material and cheaper but if they used cast steel they wouldn't ever have these issues. Blacksmith Anvils are made of Cast steel.
Posted by: Ed McMorrow, RPT

Re: Cracked plate - now what? - 04/21/13 03:50 PM

From looking at the pictures I don't see excessive string bearing angle over the treble bridge which is what I would expect to see if the plate was forced to bend so much that it cracks. The bridge and board look original so the pin-block would have to be too thick for that to happen-and the angle of the string between bridge surface and speaking length do not look like the string plane is going uphill to the pin-block. Since there are two cracks in the treble most strut-I suspect the plate was dropped outside the piano most likely.
Posted by: Olek

Re: Cracked plate - now what? - 04/21/13 07:00 PM

old iron can be brittle, and that plate have zero flexibility, very tall and massive, but there must be some rocking motion from the pinblock, may be not well adjusted.
Posted by: Ed McMorrow, RPT

Re: Cracked plate - now what? - 04/21/13 08:43 PM

I have not noticed any age related brittleness in old plates. What mechanism would produce deterioration in grey iron under static load. They do not bend (plastically deform) over time in any detectable amount.

Steinways are typically bowed over the nose bolts by a little bit. Some plates will spring up 10mm at the tail.
Posted by: BobbinBlueJay

Re: Cracked plate - now what? - 04/21/13 11:42 PM

I have experience with gas welding and brazing particularly with tubular steel frames. I know enough from that experience to know how hard it would be to gas weld a cast iron frame like this. I've only tried my hand at TIG welding once, at least to get a feel for it. I can believe in the right hands maybe TIG welding could work.

I'm also an architect with good background in structure. I had a great lecture in school about the history of iron and steel making. In the late 1800's you could read a building's structure by which parts were cast iron and which were wrought iron. I know that cast iron works in compression and can't take tension and therefore bending. These cracks come from bending somehow and the crack is on the tension side of the bend. Trusses are designed to have pinned joints at intersections of members so that every member stays in pure tension or compression, but a single casting like this will put the members in bending if the whole thing is racked. It's more like a Vierendeel truss. Yup, steel (and wrought iron) can take tension and therefore bending, so a steel plate might fair better.
Posted by: Ed McMorrow, RPT

Re: Cracked plate - now what? - 04/22/13 01:17 AM

My understanding and experience with grey iron plates is that they will bend, (as in flex) but they will not deform, (bend permanently). They break when the flexing exceeds the strength. In essence they exhibit no plastic deformation from any load they carry. When the load is removed the casting returns to it original state.

A shock load distributed into the structure behaves somewhat chaotic in that the first impact point and any others that follow can magnify or cancel the distortion waves that move through the structure depending on timing and resultant combination vectors.

Grey iron has tremendous compressive strength but much less tensile strength.
Posted by: Olek

Re: Cracked plate - now what? - 04/22/13 05:18 AM

Ed there are different qualities of lamellar grey iron. The old one harden, due to phosphorous content in the often local mineral used.

That makes if memory serves a migration of carbon within the iron.

But I say that by memory, informations from iron molding association.

Also plate design of Steinway is poviding an "active" plate with thin braces , the sound of the plate is coloring the piano tone.

The plate pictured is passive type with massive braces in my opinion.

Bend way less , not intended too, those types of plates are not on dowels generally but on wood blocks , and the case can be more sonorous , the piano having a more soft and mellow tone then.

But I will have confirmation of those design points soon.
Posted by: kpembrook

Re: Cracked plate - now what? - 04/22/13 11:20 AM

Originally Posted By: Ed McMorrow, RPT
I have not noticed any age related brittleness in old plates. What mechanism would produce deterioration in grey iron under static load. They do not bend (plastically deform) over time in any detectable amount.

Steinways are typically bowed over the nose bolts by a little bit. Some plates will spring up 10mm at the tail.


Actually, the automotive engine building companies used to dump engine blocks in a field for a couple of years to cure before machining them. Cast iron does "move" after it has cooled.

It is to that factor that I attribute the springing up of plates (S&S & others). The assumption is that the installation was "stressless" but over time the plate or rim (or both) developed stress which is relieved when the plate is taken out.
Posted by: Olek

Re: Cracked plate - now what? - 04/22/13 02:31 PM

A small bending up may relieve the strain from the tuning pins on the beginning of the braces , just a theory I heard, but not totally wrong.

How much should be the question...

I find about 34 mm at the tail of a recent Koncert 275 Boesendorfer. Not really impressing the factory guy I asked about .but their plate is not supposed to be torqued I believe.

Posted by: Ed McMorrow, RPT

Re: Cracked plate - now what? - 04/22/13 09:51 PM

Keith, I have watched new Steinways having the plate installed and they bow them a little over the nose bolts. They call this part of "building tension into the piano".

Olek, what chemical change can occur in a casting that is warm and dry in a typical house? My understanding of grey iron in these circumstances is that it behaves like an inert substance. There is no way that I know of for ionic or covalent chemical bonds, nor the crystalline structure to change without great heat being added.
Posted by: kpembrook

Re: Cracked plate - now what? - 04/22/13 11:59 PM

Originally Posted By: Ed McMorrow, RPT
Keith, I have watched new Steinways having the plate installed and they bow them a little over the nose bolts. They call this part of "building tension into the piano".

Olek, what chemical change can occur in a casting that is warm and dry in a typical house? My understanding of grey iron in these circumstances is that it behaves like an inert substance. There is no way that I know of for ionic or covalent chemical bonds, nor the crystalline structure to change without great heat being added.


Good to know, Ed. I'm still learning.

However, Steinway's practice doesn't necessarily invalidate the ongoing "curing" of cast iron, though. I've found plates warping up off nosebolts when unscrewed. If the only source of tension was cranking up the nosebolts, then they should be the highest point of support and the plate should remain in contact with them while floating above some point or points on the rim.

Of course, another factor that could account for part (or most) of the phenomenon is the warping of the rim. Particularly being wood, stresses could develop which were in balance when the rim was first made but were released as the wood cures over the years.

I'm sure you've experienced removing the plate from a piano when it appeared to have no tension in relation to the rim and then after repairing the soundboard the plate doesn't want to "lay down". Where does that come from? I have concluded it must be the rim -- which had been immobilized -- releasing stress, perhaps in combination with the drying process of preparing the board for shimming.
Posted by: Olek

Re: Cracked plate - now what? - 04/23/13 03:54 AM

Ed I find that :
A statistically significant increase in strength by aging at room temperature was observed in 23 of 25 independent studies in nine different foundries. This increase in resistance was 3.3% up to 13.5%. Curve as a function of aging time has a logarithmic form, the majority of aging occurring during the first ten days of storage. This increase in resistance is a function of time and temperature and can be accelerated by maintaining the specimens at temperatures between 85 ° C and 285 ° C prior to testing.

The original doc is in French unfortunately

http://cat.inist.fr/?aModele=afficheN&cpsidt=16806145

It is also noticed as bore a hole in an old piano plate can show a more hard material than expected sometime.

I was said it was a chemical process due to impurities in the cooked mix (phosphore). the same which is responsible for permanent deformation if one part of the plate is heated for welding (again that is not my specialty, I am just trying to have some global understanding)
Posted by: Olek

Re: Cracked plate - now what? - 04/23/13 04:03 AM

Originally Posted By: kpembrook
Originally Posted By: Ed McMorrow, RPT
Keith, I have watched new Steinways having the plate installed and they bow them a little over the nose bolts. They call this part of "building tension into the piano".

Olek, what chemical change can occur in a casting that is warm and dry in a typical house? My understanding of grey iron in these circumstances is that it behaves like an inert substance. There is no way that I know of for ionic or covalent chemical bonds, nor the crystalline structure to change without great heat being added.


Good to know, Ed. I'm still learning.

However, Steinway's practice doesn't necessarily invalidate the ongoing "curing" of cast iron, though. I've found plates warping up off nosebolts when unscrewed. If the only source of tension was cranking up the nosebolts, then they should be the highest point of support and the plate should remain in contact with them while floating above some point or points on the rim.

Of course, another factor that could account for part (or most) of the phenomenon is the warping of the rim. Particularly being wood, stresses could develop which were in balance when the rim was first made but were released as the wood cures over the years.

I'm sure you've experienced removing the plate from a piano when it appeared to have no tension in relation to the rim and then after repairing the soundboard the plate doesn't want to "lay down". Where does that come from? I have concluded it must be the rim -- which had been immobilized -- releasing stress, perhaps in combination with the drying process of preparing the board for shimming.


I agree, releasing stress on an original piano must be done knowing that it may have been part of the sound of the piano.

A dangerous situation, and one cannot avoid to think that the braces and rim have also moved under the stress and with age.

But I believe that whatever acceptable tension within the piano case and plate, must be left if one want to find back the tone (I feel it have to do with the response time of the instrument)

Piano rebuilders most often use a no or little stress solution when it comes to plate, I believe.

A good understanding of the material used and the one of the plate design should help, while this subject is often left untreated, in my experience.
Posted by: kpembrook

Re: Cracked plate - now what? - 04/23/13 08:23 AM

Another example that something is going on that cannot be attributed to any factory procedure is the wedge at the plate horn. How often does that just fall out after the string tension is released? Supposedly, it was driven in tight before the piano was strung up. Decades later, it just falls out -- or can be easily removed by hand before the plate is unscrewed from the rim.
Posted by: Jeff Clef

Re: Cracked plate - now what? - 04/23/13 11:01 AM

Sell this handsome, but short, instrument to a decorator. Many pianos serve a purely ornamental purpose, and are only purchased so that the maid will have something else to dust. This will spare a working instrument. The owners would never find out whether it could be played or not, and if they did, they would be pleased to learn that it never needed to be tuned. And the daughters of the family would be pleased to learn that they could be excused from piano lessons.

If they should find that they want a piano that works, they might have the bucks and the risk-tolerant attitude to attempt the repair. Meanwhile, you are free to believe that this would happen.
Posted by: BobbinBlueJay

Re: Cracked plate - now what? - 05/14/13 02:33 PM

<Bump after a bit of a pause.>

Originally Posted By: Jeff Clef
Sell this handsome, but short, instrument to a decorator. Many pianos serve a purely ornamental purpose, and are only purchased so that the maid will have something else to dust.
...


Actually, talking to the tuner, he did say he once had to gut a piano for a stage production that wanted a prop that stage hands could get on and off stage between scenes, so I guess there is some need for prop pianos.

He voiced a concern for possible further violent movement with a failed plate like this by just touching it, moving it or starting to dismantle it. Any thoughts on de-tensioning the strings? Backing off each string a little at a time in any particular order so as not to create a greater imbalance of forces and catastrophic failure?

Though I'm not sure I'm up for the repair path, but it might be nice to know if there are any such talented TIG welders in this area (New York to Boston). You would think so given Connecticut is home to so many fabricators of jet engines, submarines, helicopters and firearms