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#2323929 - 09/04/14 04:07 AM Plate trouble
thepianodoctor Offline
Full Member

Registered: 02/21/07
Posts: 45
Loc: Northern Ireland
Hello all

It's been a while since I was on here.....it's also been a while since I did a full restoration, and Im having a bit of bother getting the plate back into the Bechstein Model III (1880).

Everything else seems to be fine....put the plate back in, in the same position I took it out, and now the front left corner is sitting way too high. I turned out the screws around the edge of the plate and this seemed to alleviate the problem slightly (but not fully). In this piano, the pin block is screwed into the plate, then glued into the stretcher which, in turn, is held securely in place by two fairly sizeable screws at each side through the cheeks.

There are 3 nose bolts (there is one on the left, mid-way down the piano, and two more at the front right side near the pin block. I have, of course, also tried lowering the one on the left side, but when I heard a distinct sound of cracking wood.....didn't want to turn it too much more!!

Is it acceptable to just push the plate down by weight, turn in the screws through the cheeks and into the stretcher to hold the front of the plate down, then shim under the edges of the plate at the rim and turn in these screws?

Anyone else had a problem like this?

Many thanks all

Mark


Edited by thepianodoctor (09/04/14 04:09 AM)
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#2323949 - 09/04/14 07:12 AM Re: Plate trouble [Re: thepianodoctor]
Mark Cerisano, RPT Offline
1000 Post Club Member

Registered: 01/24/10
Posts: 1495
Loc: Montreal, Quebec, Canada
Cast iron has very little strength in tension. I would be hesitant to do that but I'm saying that more as an engineer than a rebuilder.

Maybe look under the plate for anything on the way.

Do you remember the plate popping up on that side when you removed the bolts? That would indicate a warped plate but I'm not sure if plates can even warp. Maybe someone else with experience can comment.

If the plate has warped, you might be able to reduce any tension in the plate by tightening the bolts gently then increasing tension on the strings and alternating between the bolts and strings. Theoretically this should work but I wouldn't do it unless someone with more experience confirmed the procedure.

My experience as a technician tells me there's something else wrong.
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Mark Cerisano, RPT
www.howtotunepianos.com

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#2323971 - 09/04/14 08:57 AM Re: Plate trouble [Re: thepianodoctor]
Johnkie Online   content
500 Post Club Member

Registered: 06/04/11
Posts: 740
Loc: England
Just a thought, but have you tried how it fits without the new pin block ? Seeing as this model has the block screwed to the frame, it may be an ill fitting block that is causing the frame to warp.
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#2323996 - 09/04/14 10:24 AM Re: Plate trouble [Re: thepianodoctor]
Ed McMorrow, RPT Offline
2000 Post Club Member

Registered: 12/09/12
Posts: 2423
Loc: Seattle, WA USA
Almost all Steinway grands have the plate installed so the hitch pin side of the casting is pulled down 1 to as much as 7mm over the height of the nose bolts. I don't like 7mm plate bow! The order of plate fastener tightening is important. Pin-block screws first, than perimeter bolts, then nose bolt nuts, and lastly if it has it the screws on the nose flange. Nose flange is the plate area that intersects with the belly rail between the bass and tenor sections.

I have too little Bechstein experience to comment if they do something similar. I have seen several cracked Bechstein plates. I have only seen two cracked Steinway plates in my entire career.

If you are bowing the plate to get it to contact all of the pin-block surface-you have a problem with your pin-block. Bechstein plate struts crack where they meet the pin-block in my experience.
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#2324164 - 09/04/14 08:23 PM Re: Plate trouble [Re: thepianodoctor]
Gene Nelson Offline
1000 Post Club Member

Registered: 09/10/04
Posts: 1533
Loc: Old Hangtown California
Full restoration meaning new pin block, new soundboard, new bridge caps etc???
Did you take reference measurements of original plate height in relation to top if outer rim?
if you have a dial indicator you can use it to tell you if turning nose bolts counterclockwise is causing the plate to rise - it will help you figure out if it is holding up the plate.
I like to have all of the plate bolts around the rim tight before adjusting the nose bolts.
If the plate won't go back to its original position it is best to just take the time and figure out what is interfering as opposed to pulling it into place with screws imho.
Iron will fracture easily and it is not a good idea to bend it as part of the seating process. imho
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#2324200 - 09/04/14 10:47 PM Re: Plate trouble [Re: thepianodoctor]
Olek Offline
7000 Post Club Member

Registered: 03/14/08
Posts: 7904
Loc: France
No one is at ease with the bowed or bowing plates , while the tail part accept rises way more than expected (16 mm leaved cold the Boesendorfer factory guys, on a Koncert 275 for instance)

WHat is new is that some piano Buildder from Bechstein assure that reinstalling that stress at reinstallation was fighting inner plate tension, or in some way helps the plate to be in a less stressed situation once the strings will be on.

He was in no way able to tell why the plates where that way, as I doubt of today or before then any factory install purposely that stress, it is however possible (and certain )that some grey iron plates cannot be as flat as intended, while the rim is .

remember those are grey iron plates, not spheroid iron, that can be molded with precision in vacuum process without as much reaction to cooling.

the mold is curved to compensate for the stress reactions during cooling, the plates are cook/heated a second time to destress them .
for what I noticed, that plate tension is making the piano more reactive (together with compression crowning )and loosening totally it may give a slower tone production.
.
As wood seem to be made more resonant with tension the plate may be an opportunity to be use as a member of the system, not only to hold the strings, but to transmit it more efficiently to other case parts.
ANyway that may be part of the concept on some instruments I worked on, that have a resonant enough case and braces to be impacted by the stress once the strings are on.

AND nose bolts last, if the plate is installed stressed it is NOT from there.




Edited by Olek (09/04/14 11:02 PM)
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#2324202 - 09/04/14 10:55 PM Re: Plate trouble [Re: Ed McMorrow, RPT]
Olek Offline
7000 Post Club Member

Registered: 03/14/08
Posts: 7904
Loc: France
Originally Posted By: Ed McMorrow, RPT
Almost all Steinway grands have the plate installed so the hitch pin side of the casting is pulled down 1 to as much as 7mm over the height of the nose bolts. I don't like 7mm plate bow! The order of plate fastener tightening is important. Pin-block screws first, than perimeter bolts, then nose bolt nuts, and lastly if it has it the screws on the nose flange. Nose flange is the plate area that intersects with the belly rail between the bass and tenor sections.

I have too little Bechstein experience to comment if they do something similar. I have seen several cracked Bechstein plates. I have only seen two cracked Steinway plates in my entire career.

If you are bowing the plate to get it to contact all of the pin-block surface-you have a problem with your pin-block. Bechstein plate struts crack where they meet the pin-block in my experience.



Yes -

Bechstein cracks it may be due more to the stress of a moving block on a brittle part of the plate.

I have a rough idea on how slighly bend plate may help the struts attachment to resist better to strings tension and stress from the block but I am far from certain to have a complete picture of the process.

Lines of tension in the plate/block strings assembly, I just hardly can figure out


Edited by Olek (09/04/14 11:01 PM)
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#2324210 - 09/04/14 11:09 PM Re: Plate trouble [Re: thepianodoctor]
Olek Offline
7000 Post Club Member

Registered: 03/14/08
Posts: 7904
Loc: France
We see that rise because we treat the nose bolts last when dismounting and last when mounting, so they show a stress that is not installed from then but on the perimeter.
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It is critical that you call your Senators and Representatives and ask them to cosponsor S. 2587 and H.R. 5052. Getting your legislators to cosponsor these bills


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