Plate Bushings - was Re: Bushing vs. bigger pin?

[Ron Nossaman]

>Ron;
> An observation and question if I may........
> This is what happens to *5 ply* pinblocks. :-)

Ah yes, right. The more laminations, the less it seems to happen (given
similar material). It's also tied in to the frequency and amplitude of
humidity swings. The more often, and broader the swings, the more damage is
done to the block. 



> Although I have never seen this phenomenon that could not be attributed to 
>the hole being drilled to close to the plate.  

I don't think these were all that mis-drilled. Sighting down the edge of
the hole from above indicated to me that the pins were probably pretty well
centered originally, and I don't recall all the pins being against the
plate when the piano was delivered. That's one of the things I tend to
notice. In this case, it looks like the block has just crushed that much. 


>S&S 'normally' drills their 
>web holes at 90 degrees to the web surface and drills their pins at from 5 to 
>7 degrees rake...right?   With these supposed "facts" in mind...was the top 
>of the pin or the bottom of the pin touching the plate?  (top and bottom 
>being relative to that portion of the pin which is inside the web arpeture.)
>Jim Bryant (FL)

Good point. All the pins were contacting the top of the plate hole, as
would be the case if they had been centered originally. This brings up an
interesting point, thank you. Conjecture: If one drilled the pinblock with
the bit indexed against the back (hitch) side of the webbing hole, so the
pin/plate contact spot was at the level of the top of the block at
assembly, how would it affect the longevity of the block? Pin torque? With
the plate taking the bulk of the string tension load, the block would get
an easier ride from the resultant leverage change. I know this happens
altogether too frequently by accident, and with a low elastic recovery high
density block, it's a disaster, but with a 5 ply quarter sawn maple block????? 

A pin in an ovalled out hole (any block type) can still have adequate
torque even though about a third of the surface area that's in the block
isn't actually touching the block. That is, until it contacts the plate.
That's when that dense, low elastic recovery block won't provide enough
friction to hold the string torque, and a more resilient block might???

If I had the funding, adequate lab facilities, someone to teach me how to
run the instrumentation, and someone else to do the paperwork and keep the
suits out from underfoot, I think I could go for a very long time without
running out of shiny little mysteries to chase down. Now that would be a
great job.


Ron N