Pinblocks and o/s pins

[Bill Ballard]

At 10:03 AM -0700 5/12/02, David Love wrote:
>When stringing a piano with oversize pins.   What method do people 
>use to prepare the old block.  I've >been reaming with the gun 
>cleaning stiff bristled brushes, but I wonder if there isn't a 
>better and more >consistent way to get to fresh wood.

That's the best that I can do, to slough the dead wood off the tuning 
pin hole walls with a gun bore brush. What with far more turning in 
the middle sections, and the bass undergoing far more prying forces 
due to the thicker plate web, I wouldn't expect to find consistent 
wear on the tuning pins holes, across the block. On a block needing 
oversized pins, it frequently takes a 4/0 pin in the middle to feel 
identical to an original 2/0 up in the top treble of the block. So it 
would take 10 mils of stock removal to equalize the pin torque 
between these two holes. And that's not answering the question of 
how that 10 mils should be tapered down from the loose pin hole in 
the middle to the tight one in the treble. So consider adding 5 mils 
to the stock removal and increasing the pin size to 5/0.

So you've got the entire set of holes re-bored (hopefully) at .296". 
Given that the original difference between bore and pin diameter 
might be anywhere from .031" to ".020" (a .281" pin in a hole bored 
at either .250' or .261"), what size pin would be needed for this 
re-bored hole, .265" or .276"? Remember, you just pulled a .281" pin 
out of there which was a loose enough fit to require some sort of 
repair, suggesting that the hole size might not be more than a few 
mils down from .281".

Re-boring to get fresh wood is another matter entirely. Were we 
supposed to do this with a hand drill? The one person I knew who did 
this successfully was going .250" into marine plywood. The tolerances 
in re-boring are far more critical. So much so to require re-boring 
with a drill press. Unless the pinblock can just be lifted out of the 
rim, it will require an "on-the-piano" drill press. Several good ones 
have been described recently: one in the Journal within the last 
year, and Terry Farrell's overhead version.

Oversized pins in the original block always contains an unknowable 
risk: how is the pin size going to feel immediately after stringing, 
and five years hence. I'd judge the block by how good or 3/0 placed 
in a weak spot feels. The lousier it feels, the greater the 
inconsistency you're going to ask the procedure (brushing/boring) to 
overcome.

Maybe Epoxy reinforcement is a viable technique here, but even the 
one paper I've read on it (from Epoxy Technology, the report of an 
antique piano conservator) described it as plugging the tuning pins 
holes and then re-boring (for 4/0 pins when replacing 2/0s).

Bill Ballard RPT
NH Chapter, P.T.G.

"There are fifty ways to screw up on this job. If you can think of 
twenty of them, you're a genius......and you aint no genius"
     ...........Mickey Rourke to William Hurt, in "Body Heat", discussing arson.
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