[pianotech] Curved cast iron plate question

[Terry Farrell]

Hi Chuck. I don't specialize in S&S, but I'll stick my neck out anyway  
(you do have a delete key, correct?) - and take everything I write  
with a grain of salt. My best guess is that the plate webbing was flat  
when cast in Springfield, Ohio. The string tension over the years has  
bowed the pinblock and plate along with it. Maybe the pinblock had  
come unglued from the stretcher (not that the stretcher has much  
strength anyway) contributing to the ability of the string tension to  
bow the plate/pinblock. Are we sure the plate isn't cracked - like a  
fore-aft strut, again allowing movement? I don't know how common a  
1/4" warp is.

I know such warping is common on real old pianos that didn't have a  
full plate (I'm talking 1850s or so when you had a hitch plate and  
fore-art struts bolted to the hitch plate and otherwise unstiffened  
pinblock).

Did the string heights reflect the 1/4" warp? Perhaps a good way to  
tell if the warp was original would be to measure original pinblock  
thickness accurately. You state that the original pinblock was shaved  
down on the ends to conform to the bowed plate. Do you say that based  
on thickness measurements, or simply because the block mated to the  
plate (the block could be warped just like the plate)? Or did you  
measure the block and found that it is 1/4" thicker in the middle and  
tapered on the upper side to mate? Is the block shape a plane on the  
bottom?

Interesting. Now the next question might be do you want to shape the  
new pinblock to mate to the presumably deformed plate, or should you  
make a planar block and screw the plate tightly to it trying to bend  
it back a bit (don't know how much you can really bent it - it likely  
has a vertical flange on the very forward edge that goes up against  
the stretcher - you'd sure think that flange along with the plate  
flange would make for a pretty darn stiff plate webbing area.

So, how's that for speculation? Hey, no one else responded, at least  
this way you don't feel all alone...... ;-)

Terry Farrell

On Sep 14, 2009, at 11:39 PM, Chuck Behm wrote:

> Hi - I've got a question for those of you who specialize in Steinway  
> rebuilds. A technician in my Guild chapter brought a plate to my  
> shop asking me to fit a pinblock to it. It's from a Steinway M, and  
> what seems unusual is that the plate is bowed in the webbing area  
> from side to side. I have the plate upside down on sawhorses, and if  
> you put a straightedge from side to side across the area for the  
> pins, there is nearly a 1/4 inch gap in the center. The original  
> pinblock had been shaved down on either end for a tight fit without  
> any filler of any kind. I've got a plan for fitting the new one, but  
> that's not the question. What I'm wondering is how unusual is this?  
> Have any of you seen this type of thing before? The rebuilder who  
> brought it in to my shop has been around longer than myself (Frank  
> Ludnak of Traer, Iowa), and he said he had never seen anything of  
> the kind before. I would have guessed that a plate with that amount  
> of deformity would have been sent back to the melting pot, or was  
> this curvature done intentionally for some reason I'm not grasping?   
> Chuck