Downbearing - Setting with a loose board

Overs Pianos sec@overspianos.com.au
Sun, 17 Oct 2004 19:51:46 +1000


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>>Someone else suggested temporarily screwing the soundboard down to 
>>the rim - I like that idea.
>
>That's what I do too. The plate, treble cap, and damper guide rails 
>cover the holes afterward.
>
>Ron N

Same here also. We use the Baldwin plate mounting system, so the 
original inner-rim bolts holes are plugged before the sound board is 
fitted. This allows us to screw the board down at the perimeter-bolt 
locations. This is similar to Dale's idea of screwing the board down 
where the plate height dowels will be fitted. Along the bass side our 
sound board installation clamps are used, and along the cut-off 
standard clamps can be used since our sound board panel doesn't cover 
the corner.

The plate height, at the rear, is set initially by placing a wooden 
block between the loose board and the plate. The board can be either 
screwed in with screws, or the perimeter bolts (which have been 
converted to thread into the plate, by fitting threaded inserts into 
the original plate holes) can be screwed down to the loose board to 
hold it in place. To establish the new bridge heights, we use a 
series of in-house manufactured blocks, with a cap screw (threaded 
into the top face of the block) for height adjustment. Using four 
blocks per string section (first note, last and two intermediates), 
the blocks are positioned so that the cap screw head is located where 
the speaking length termination will be for the new bridge.

A nominal stringing-pillow height is assigned to each sample note 
prior to setting the height of the adjustable blocks. These stringing 
pillow heights are varied slightly to fine tune the downbearing 
before the piano is strung.

We don't wedge the board down to pre-load it prior to setting the 
bridge height/down bearing. Since the downbearing loads are 
quantifiable, it is possible to predict the sound board drop when 
under load. The desired final down bearing angle, and the loss of 
angle predicted under down bearing load are added together to arrive 
at an unstrung initial down bearing setting for each point.

Ron O.

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OVERS PIANOS - SYDNEY
   Grand piano manufacturers
________________________

Web:    http://www.overspianos.com.au
Email: mailto:ron@overspianos.com.au
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