----- Original Message ----- From: Ron Nossaman <RNossaman@KSCABLE.com> To: <pianotech@ptg.org> Sent: March 08, 2000 6:54 AM Subject: Re: Baldwin torque, (was survey) > The reported reason for using the infinite layered pinblock is that it > isn't as prone to degradation through the years because it doesn't react > much to humidity changes. By my experience, it does react quite obviously. > Given the fact that there is very little resilience to the material, that > is very little recovery or spring back from compression, the torque > readings from low to high humidity periods will be substantially different > even though the block dimensions don't change much. Even so, they seem to > age relatively well, generally, but you will find the individual loose pin > more often than in less dense blocks. At least that's what I have found. ---------------------------------------------------------------------------- ------------------------------------------- Ron, et al, The process used by Baldwin to make their grand piano pinblocks is a slightly modified version of one developed during the 1940's to make a resin-treated compressed wood product known as "Compreg" - or "compressed, impregnated wood. A paper written for the U.S. Dept. of Agriculture by the Forest Products Laboratory in 1951 discussed the development of this process and the characteristics of wood based products made in this manner. This material was originally developed to form the engine mounts (stringers) found in wood hulled mine sweepers. Being non-magnetic, it would not trigger mines designed to detonate in the presence of ferrous metals. It had the advantage of being both harder and somewhat more reliable than brass in this application. Compreg is a treated wood product that is made of wood and resin-forming chemicals (typically phenol- or resorcinol-formaldehyde) that act as plasticizers for the wood so that it can be compressed under high pressure to a specific gravity of 1.0 to 1.4. Several different resins were tried while the process was being developed, but the most successful was, and still is, water-soluble phenol-formaldehyde resin. In making Compreg, wood veneers are treated with water-soluble phenol-formaldehyde to a level that will result in a resin content of 25 to 30 percent based on the ovendry weight of the wood. The resin is allowed to dry without curing at temperatures below 30º C (approx. 175º F). The resin is actually cured later on during the heating and densification (compression) process. Panels are made by stacking treated veneers of the required thickness and quantity in a hydraulic press, then heating and compressing them to a specific gravity of approximately 1 to 1.4. In the original Compreg process, temperatures of 150º C (300º F) and pressures of 1,000 to 1,200 lbs/in2 (70 to 85 kg/cm2) were used. The Baldwin process uses similar temperatures -- this is required to cure the adhesive -- but lower pressures, hence, the density of the Baldwin pinblock is somewhat lower than the maximum that the process is capable of, but it is still quite high. (By the way, with some variation in detail, similar processes are used to make Delignet and Falconwood blocks. Falconwood being the more dense of the two, if memory serves. In these products beech is used instead of maple, but the adhesives are similar as are the temperatures and pressures.) The resulting material is well on its way to being a fiber-reinforced plastic (FRP) and has several characteristics more like those of FRP products than of wood. Indeed, with the exception that kraft paper is used instead of maple veneer, this is nearly the same process that is used to make Formica and other such "plastic laminates". Compreg does have certain characteristics which would seem to make it a good material for piano pinblocks: 1) It is very stable when subjected to humidity and temperature cycles. 2) It resists cracking and splitting. 3) It has high compression strength. It was probably these characteristics that led Baldwin and other to use these materials in the first place. Unfortunately, it has several other characteristics that make it unsuitable for use as a piano pinblock material: 1) Springback (after compression), or resiliency, is very low. - A material with low springback will simply deform when compressed. - When the tuning pin is driven into the pinblock it compresses the wood and depends on the woods ability to "springback" to hold it tight and maintain good, consistent tuning pin torque. 2) Hardness is 10 to 20 times that of normal wood. 3) Impact strength ("toughness") is about 1/3 to 3/4 that of normal wood, but this is very susceptible to the variables of manufacture. - The impact strength of the pinblock material is the quality that prevents the pinblock from being damaged while the pin is being driven into the tuning pin hole. - The reduced impact strength, or toughness, of Compreg allows the pinblock to be easily damaged as the piano is being strung. 4) Machinability is decreased. True Compreg takes on some of the characteristics of metal and in some cases requires metal working tools for machining operations. 5) It is possible to burnish material to a very smooth, glossy surface. - This is the characteristic that leads to "jumpy" pins in pinblocks made with these materials after several years in use. Obviously these materials can be used to make piano pinblocks. As the density of the material goes up, however, so do the potential problems. They become more critical to variations in manufacture. Slight variations in hole diameter that would be insignificant in a more resilient material become critical in these blocks. The difference between a loose set of pins and a tight set is slight indeed. Pianos that leave the factory with relatively consistent pin torque can develop random loose pins over relatively brief periods of time. (By the way, the reason you don't have these problems with Baldwin vertical pianos is that they are built differently. The traditional high-density Baldwin grand piano pinblock is fairly expensive to manufacture. Much to expensive to put in the more mass-produced verticals. Consequently, the verticals actually have a much better pinblock. At least in my opinion.) This is probably more than you ever wanted to know about this stuff. Regards, Del. PS The above is from a work I have written for future publication. Hence the notice below: Copyright (C) 2000 This material may not be copied or reproduced in any form without the authors permission.
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