Why Cardboard Shim?

[maxim_tuner]

https://youtu.be/SqYdjUbCpak?si=YmJ4XTJl6IQNaB0u
The idea of a cardboard shim is not a makeshift (Jerry-rigged) or temporary solution to address the proper functioning of the tuning pin. It is, in fact, the most rational and appropriate solution in this case. Here's why:
The classical school of piano tuners asserts that the "tuning pin" is essentially a nail, and accordingly, they treat it as a technical tool, initially driving it in when the pin can no longer maintain the desired string tension, and subsequently, when even that ceases to work, resorting to the hammer and mallet as the primary means of resolving the issue. But is such an approach truly correct? Absolutely not.
If we examine the piano tuning pin closely, we will find that it has a right-handed thread. Opponents may argue that this is done to facilitate the removal of the pin from the pinblock (by unscrewing it) during repair work. However, let's consider the mechanism of the pin's operation within the pinblock. The pin, made of a rigid metal alloy, is firmly secured by up to 100 kg of string tension in the wooden pinblock hole. Even immediately after the factory installation, it begins to exert firm pressure in two opposing directions, without any radial rotation in the hole - its visible part, where the string is located, presses on the lower part of the bushing, while the submerged, reverse side, which is directly in the pinblock hole, presses upwards. Three-quarters of the working part of the pin are located at a significant angle in the hole (bushing + pinblock), and as a result, they must "move" not radially, but in a wedged position. This leads to gradual wear of the wooden hollow cylindrical shape of the hole, i.e., we are rotating the pin not in a hollow cylinder, but in a cylinder with two conical sides. Therefore, after some use, the pin "fails" to maintain the desired string tension.
Incidentally, the pin, being primarily a screw, rotates in the hole due to the presence of its thread. And yet, we ignore the basic principle of the pin having a thread and reach for the mallet when it comes to "treating" the seating area for the pin (the pinblock hole). This is a criminal and extremely unwise course of action.
Yes, we have installed a shim (of any material) and driven the pin into the pinblock hole. What happens as a result of such a procedure? First, it is impossible to determine the appropriate force of the hammer blow on the pin. If a 4-pound hammer is used to strike the pin forcefully, there is a high probability that the shim will be displaced in the hole, resulting in a rigid, disintegrated positioning of the pin. The pin will "crawl" into the hole crookedly, partially destroying it. Secondly, even an experienced tuner, as a rule, does not know the full condition of the hole, and even when applying appropriately correct hammer blows to the pin, can still make mistakes, as the human factor comes into play. If the tuner strikes the pin with weak force, the pin will gradually sink into the hole, "pressing" against the hard shim. As a consequence of these weak blows into the "new hole with the shim," there is a significant risk that the hard shim will considerably damage the inner walls of the hole, leaving only enlarged cracks and increasing the wood's friability. Conclusion: using a hard shim and driving the pin in is an incorrect method.
So, what is the solution? Using a hammer is not possible, and installing a rigid shim is also problematic... This is where the moment of truth arises. If the pin is not driven into the hole, but rather rotated in it, then it is necessary to use something relatively soft as a shim. Yes, you can use poplar or linden wood shavings, but never oak.
As a result of practical experiments, Max decided to use a 3mm corrugated cardboard shim, which is cut at a 45-degree angle to increase its rigidity due to the ridges. The shim is gently compressed with the fingers, inserted into the hole, and screwed in using a T-bar wrench. During the careful screwing in of the tuning pin, the shim partially disintegrates into fibers, which fill the cracks and voids in the wood, and the 4% glue content in the corrugated cardboard also elastically distributes the semi-cylindrical strip along the entire hole in the pinblock. This procedure can be performed by any layperson "rescuing" their own old, dilapidated piano. Slowly but surely, tediously but reliably.
regards,
Max