You can drill the holes through with a regular drill bit or you can use a tuning pin reamer to ream the bottom part of the holes.
I always brush the holes with a rifle bore brush (protek sells a tight-fitting one, I prefer a smaller diameter--I bought a supply of mine in a Walmart at sporting goods dept years ago), and I twirl them as I turn the hand-hand drill. I reverse the direction every few holes otherwise the steel bristles start combing the wood rather than cleaning it.
Some then apply pure varnish (nor polyurethane) to the holes or use rosin on the pins (crush some into the pin box and shake). I dislike talc powder though it does give a buttery feel of the pins.
I gave up on trying to ream/brush holes based on the torque of original pins. Generally, the torque is too low in the tenor and low bass where the pinblocks are most likely to develop internal cracks. It is highest in the treble where it should be lowest for a nice tuning feel. I've use two sizes of drill bits to ease the torque in treble and affect it least in tenor and bass. In a hurry you can just brush the holes.
If the torque is good, consider stringing on existing pins. Have the ones in tenor and bass end up up to 3/4 turns lower and in treble as high as originally. The downside is that boosting the torque in tenor and bass this way gives you greatest torque on the bottom of the pin, which causes a spongy feel. The torque should be the same or higher close to the top. That's the reason behind hybrid blocks (multilam on top, traditional thick plies on bottom).
There may be a few other pointers in Pianos Inside Out.
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Mario Igrec, RPT, MM
Chief Piano Technician, The Juilliard School
http://www.pianosinsideout.com------------------------------
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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