if there is room for the pin to be driven, now, with strings on, deeper, the existing pins might be sufficient. that's one option, as length of threads in the block has a huge effect on torque...often 1/8" buys between 25 and 75 in/lbs depending on the condition of the block.
second possibility, is to only go up 1 size pin and retain or increase the length of the pin in the block, without sticking any drills in the hole. This longer pin lower friction per contact area, can be a real nice pin to tune.
I have an article which i've submitted to the journal, which really breaks this all down, both adjusting pin torque parameters, and understanding how to test torque for an accurate predictable result. I think its publishing at some point, in the reasonably near future.
Bottom line would be, do a test pin up at 88 and several other points in the scale. Insert it, mirroring all the moves and parameters that you will install on the real pins, exactly as you will install when doing the real stringing. ,Make sure the pins are installed at the same installed pin height off the plate they will be at when you actually string. Test your proposed theory on the test pins. if you like them, leave them in place...don't remove the pin, just string those pins as you would a broken string on-site. Measure the torque an hour after insertion and then the next morning, before deciding what your installed torque,given your test pins is likely to be. Since the test pins are bare pins, add 25in/lbs (treble), and 50in/lbs (bass), to you torque readings to get an idea what the strung at pitch torque will be.
The answer to your question has to be "test it"...but test it correctly, in a way that will give you trustworthy data.
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Jim Ialeggio
grandpianosolutions.com
Shirley, MA
978 425-9026
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Original Message:
Sent: 06-11-2020 09:49
From: Alan Eder
Subject: Deepening existing tuning pin holes prior to re-stringing
Hi All,
The Situation:
When restringing withOUT replacing the tuning pin block, one issue is that the tuning pin hole is larger where occupied by the original tuning pin, but slightly smaller beyond the tip of the pin. Problems can arise if the newly installed, somewhat larger replacement tuning pin goes into the block any farther than the original, resulting in higher torque at the bottom of the pin than at the top (undesirable, and--in the opinion of many-- the opposite of ideal).
So, what to do?
Some techs drill out the hole with a hand drill. I have not tried this, and don't know that I will, as some fairly skilled rebuilders have reported inconsistent results with this method. No doubt, some use it successfully, but they seem to be the fortunate few that "have the touch."
Other rebuilders use shorter tuning pins for the restring, to ensure not getting into the tighter part of the hole. That solves the problem under discussion, but at the cost of a compromise elsewhere.
The Proposed Solution:
I have been considering removing the strings, checking the torque of the existing pins (after measuring all of the new pins, the originals that were formerly looser would get the slightly larger ones), and then pounding IN the original tuning pins a few millimeters (remember, the strings have been removed), in order to achive a safety margin at the bottom of the hole, beyond where the new pin would encounter the dreaded "ledge." This would not take a lot of time, and so far in my mental modeling, I have not been able to think of any downside.
Has anyone ever tried this before? If you have, please share your outcomes.
Can anyone that has done lots of restringing think of a compelling reason to NOT do this? Inquiring minds...
Stay safe,
Alan
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Alan Eder, RPT
Herb Alpert School of Music
California Institute of the Arts
Valencia, CA
661.904.6483
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