Piano World Home Page Forums Our Most Popular Forums Piano Tuner-Technicians Forum Cracked plate - now what?

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.

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.

www.muggyweld.com is the correct website sorry

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.

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.

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

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.

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.

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.

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.

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

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.

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.

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

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.

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?

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